Cognition and Communication in the Evolution of Language · 2018-02-01 · human cultures. This is,...

Cognition andCommunication in theEvolution of Language

ANNE REBOUL

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3

The specificity of the humanconceptual apparatus

. . INTRODUCTION

As we saw in Chapter , most theories of language evolution see language as acommunication system in the strong sense that it has evolved for communication.Rather naturally, given that communication is the epitome of a communicationsystem, this has led them to propose social scenarios for language evolution. Onedeep problem regarding language is its uniqueness. This means that, even in scen-arios that see it as continuous with other animal communication systems, somediscontinuity has to be postulated to explain why no other ape has developed ascomplex a communication system. On social scenarios, this entails locating thisdiscontinuity in social factors. Here, two paths are available: the first one is topostulate a discontinuity in social organization;1 the second one is to locate thediscontinuity in a change of social attitudes. This second path has been chosen byTomasello (see, e.g., Tomasello , ), who argues that humans are uniqueamong primates (including apes) in being altruistically cooperative.2 This claim isjustified on the basis that humans are ready to help even strangers that they meet on aone-off basis. This, or so it is argued, is enough to show that human cooperation isnot due to reciprocal altruism (see Trivers ), as in reciprocal altruism organismshelp others who will in return help them later on (in other words, it is a form ofdelayed mutualism, in which both the agent and the recipient benefit in the end).Given that helping a stranger that one will never meet again prevents any hope ofsuch reciprocity, human cooperation is altruistic, rather than reciprocal, showing adeep change in pro-social attitude in humans as compared to apes. There areproblems with this argument, the main one being that such help towards strangers,

1 Dunbar’s account (, ) (see Chapter ) falls under that description. As we have seen, it meetswith serious difficulties.

2 As we saw in Chapter , altruism characterizes actions that are beneficial for the recipient, butdetrimental to the agent.

Cognition and Communication in the Evolution of Language. First edition. Anne Reboul.© Anne Reboul . First published by Oxford University Press.

while it occurs in developed societies,3 seems extremely restricted if not entirely non-existent among people living in hunter-gatherer societies, where strangers may beoffered violence rather than help (see, e.g., Keeley , and, on a more anecdotalbasis, Diamond and Chagnon ). Incidentally, a look at history may makeone doubtful of human benevolence (see Kershaw ; Lifton ; Pinker ).What may even be a more serious counterargument is that it is not clear that thesimplistic slogans ‘Nice humans, nasty apes’ or ‘Cooperative humans, competitivechimps’ are really supported by a careful comparison of social attitudes (as mani-fested in action) between humans and apes. For instance, it has been shown thatchimpanzees can cooperate in hunting (see Boesch and Boesch ; Boesch a,b,, ), and occasionally act in an altruistic manner (for example, by adoptingorphans—see Boesch et al. —and effecting reconciliation—see Wittig andBoesch ). Finally, Tomasello completely ignores the second chimpanzee species,bonobos, which arguably is on a par with humans in terms of cooperation evenwith strangers (see de Waal for a general argument to that effect). Indeed,Maestripieri (: ) says:

We may think we have outgrown the conditions that govern the lives of other primates. We nolonger live in the jungle and swing between trees; instead, our homes are in or around largecities, and we drive cars, wear clothes, spend years in formal education, and communicateelectronically. Yet technology and clothes cannot disguise the inheritance of our primate past.They have simply changed the arena in which we act out age-old rituals, making the games thathuman primates play more arbitrary perhaps, but no less powerful.

In other words, the main differences between humans and the other non-humanprimates lie not in their social tendencies, but in the fact that humans have con-structed a whole new environment, made of technology, which is far beyond whatany other ape species can aspire to.4 If this is the case, it seems to argue that the maindifferences between humans and other apes lie in general cognitive abilities, ratherthan in social abilities.So the question becomes: why have humans developed such technological feats?5

One possible answer is that humans have cumulative culture, which allows them to

3 Where, by the way, arguably, this sort of help works on a sort of generalized reciprocal altruism, wherean individual helping a stranger trusts that, even though her recipient will not necessarily help in return,when she finds herself in a similar position, other individuals to whom she is a stranger will similarly help.

4 I will discuss the social accounts in more depth in Section ..5 Note that, though the differences between the technological environment in ape societies and

industrial human societies is striking, it should not obscure the technological gap between ape societiesand hunter-gatherer societies: hunter-gatherer societies were the general mode of social organization inhumans until ,–, years ago, when climate change made agriculture possible (see Burroughs on the link between the emergence of agriculture and climate change) and such hunter-gatherergroups not only left the forests where apes remained stuck, they conquered the planet and developedspecialized and composite tools and weapons, much beyond what apes do and well before the emergence ofagriculture (see, e.g., Mithen , as well as later in this section).

The human conceptual apparatus

accumulate knowledge, both theoretical and technological (on the notion of cumu-lative culture and its specificity to humans, see, e.g., Tomasello ; Mesoudi ).More precisely, cumulative culture is supposed to be the result of two main elements:conservation (the preservation of already acquired knowledge) and innovation (theproduction of new knowledge).6 The underlying idea (see Tomasello , )behind cumulative culture is that social learning is key because it means that eachnew generation does not have to begin from scratch: it can build on, improve, andinnovate on what the previous generation had already discovered. So the questionbecomes, why did humans (and only humans in that hypothesis) develop an abilityfor cumulative culture? Quite a lot of work on the question has been devoted toconservation, but relatively little to innovation. Thus, most answers have been social:humans have a species-specific ability faithfully to imitate others’ actions (Tomasello, ); humans are the pedagogical species (see Csibra and Gergely ). Inother words, humans are especially good at social learning, while, in apes, sociallearning is more limited, and may be limited to a form of socially facilitatedindividual learning.

The very existence of ‘cultural’ differences between chimpanzee groups, which iswell documented by now (see McGrew ; Boesch ), has to limit the explana-tory power of such claims. I will begin with a few words about chimpanzees, as theyhave been the most studied species in that respect. First of all, let me borrowMesoudi’s definition of the vexed term ‘culture’: ‘Culture is information that isacquired from other individuals via social transmission mechanisms such as imitation,teaching and language’ (Mesoudi : –; emphasis in original). Clearly, languagecannot be a social transmission mechanism in chimpanzees, which leaves us withimitation and teaching. Originally, it was claimed that both processes are absent inchimpanzees on the basis of experimental evidence from groups of captive chim-panzees (see, e.g., Tomasello , ). However, as Boesch () has docu-mented in his book, there is repeated evidence of both imitation and teaching in wildchimpanzees, notably (but not only, see Boesch for references) among the Taïchimpanzees, where he has done most of his fieldwork. Boesch is cautious to notethat one form of imitation that seems characteristic of young children (but is largelyabsent in human adults, see Horowitz ), the faithful reproduction of the dem-onstrator’s actions even when they are obviously irrelevant to the goal (so-calledover-imitation), is absent from chimpanzees. But, on the other hand, chimpanzeesare good at identifying others’ goals and intentions and at reproducing a demon-strator’s relevant gestures. Similarly, while the kind of active teaching that is charac-teristic of Western schooling is not found in chimpanzees, the more traditional kindof teaching that rests on demonstration and facilitation (and that is also found in

6 Another important element that has been rather less extensively discussed (although see O’Brien andShennan ) is how innovation spreads.

Introduction

less-developed human societies, where active teaching is largely absent) is also foundin chimpanzees. As Boesch () notes, this difference (apart from the fact thatWestern active teaching is largely based on linguistic communication) may be due tothe fact that chimpanzee cultures are mainly material, while human cultures are alsoimportantly social and symbolic. Material culture is especially suited to the kind ofteaching found in chimpanzees.Thus, it is not clear that chimpanzee cultures are not cumulative, and indeed a

strong indication that they are is the existence of complex sequences of actions usingdifferent tools in succession for a given goal (e.g., for honey extraction, see Boesch: figure .). What is clear, however, is that they are much more limited than arehuman cultures. This is, of course, due to the obvious fact that human cultures arealso importantly symbolic, while chimpanzee cultures are mostly material. But, evenin material culture, there are striking differences, chief among which is the completeabsence of composite tools in the material cultures of chimpanzees. Composite tools,from hammers and stone-tipped spears to cars and computers, are the staple ofhuman life. Boesch suggests that this absence may be due to the fact that chimpan-zees have remained forest-bound and arboreal, while hominines have left the forestand colonized the world beyond Africa, being thus submitted to wide environmentaldiversity. On a view on which innovation is dependent on ecological constraints (thatis, one invents what one needs), this, Boesch suggests, might explain why chimpan-zees do not build or use composite tools as humans do.It is not clear, however, that this is a tenable explanation. On Boesch’s own

showing, one important occasion of tool use in chimpanzees is nut cracking. Whilechimpanzees use (in Taï and Bossou) both an anvil and a hammer (and thus combinetools), they basically use stones as hammers, and not composite hammers made ofstone and a wooden handle, despite the fact that such a composite tool would greatlyenhance their efficiency and would make the task less effortful. An alternativeexplanation is that the construction of such composite tools is beyond chimpanzees’cognitive abilities, and, indeed, it might be argued that, rather than being purelygrounded in human sociability, human culture is as much if not more dependent onhuman general cognitive abilities.7 While this seems to leads us to the second factorin cumulative culture—that is, innovation—it is not clear that even conservation canoccur without general intelligence. Thus, arguably, conservation will sometimes reston individual learning as well as on social abilities. Over-imitation can take you onlyso far.8 If you are learning mathematics, just reproducing the steps for a givencomputation will not allow you to go very far if you do not have a minimal

7 Ambrose () links composite tool construction to new capacities for working memory and‘constructive’ memory (mental travel to the future), allowing for planning.

8 Indeed, according to Boesch (), in chimpanzees, the apprentice has to grasp the purpose of aspecific tool to come eventually to master its use.


understanding of the reason for which you have to follow them. To take an evenmore minimal example, counting is dependent not only on producing number labelsin the right circumstances or in the right order, but on understanding the recursivesuccessor principle. Even though (as argued in Tallerman ), much learning innon-industrial societies may be based on pedagogical showing and imitating (as inchimpanzees) rather than on linguistic description or explanation, this does notmean that individual learning (comprehension) is not a crucial factor as well. So,where do the clearly outstanding human abilities for individual learning come from?

In this chapter, I will argue that the major difference between humans and non-human primates lies in general cognitive abilities, notably in general abilities forabstraction, which have given humans access to extremely rich conceptual appar-atuses, incommensurable with non-human primate conceptual apparatuses.

. . CONCEPTUAL APPARATUSES

. . . INTRODUCTION

The literature on concepts covers many issues, which are not always sufficientlydistinguished. So let me begin by a bit of terminological legislation. I will use the term‘conceptual apparatus’ for the whole set of mental representations and cognitivemechanisms (not all of which are concepts, as we will see presently) that an organismuses to build and modify its Weltanschauung (its representation of the world it livesin). Conceptual apparatuses can differ between species, as do Weltanschauungen (ifanything, they do depend in part on perceptual abilities, which are highly variableamong species). I will reserve the term ‘category’ for the extension of a mentalrepresentation (for example, a concept). Thus, the set of cats is the category corres-ponding to the concept CAT.9 Two major components of cognitive apparatuses areconcepts (discussed later) and core domains of knowledge. Core domains of know-ledge, often called folk-this or that (for example, folk-psychology, folk-biology, folk-physics, and so on), constrain the way we think about the objects concerned: forinstance, we do not apply exactly the same type of reasoning to inanimate and toanimate objects. But, stricto sensu, the core domain of folk-biology (or the part of thiscore domain concerning animate things) does not constitute the concept of animatethings. Rather, it biases the attention of the organism and orients it towards someproperties (agency, self-propellation, and so on) rather than others. In other words,core domains play an important part in the accumulation of knowledge (or falliblebeliefs) that we acquire about the objects in the categories concerned. Some coredomains of knowledge (for example, folk-arithmetic) seem widely shared among

9 I follow the tradition of indicating concepts in capital letters.

Conceptual apparatuses

animal species (arguably, all vertebrates share primitive counting operations, such assubitization—perceiving small numbers—and estimating larger quantities), whileothers are more restricted and are only partly shared (for instance, folk-psychologyis partly shared among primates, but mind reading may be restricted to humans). Wewill come back to core domains (see Section ...). But the major question is thenature of concepts. In philosophy, concepts are taken to be the components of(propositional) thought, but this rough and ready characterization leaves muchthat is mysterious, and there is no consensus about the nature of concepts. Add-itionally, this definition of concepts is not shared by cognitive psychologists, with theresult that it is not clear that the very notion of concept can be given a precise sense.This has led some scholars (see, e.g., Machery ) to the radical proposition thatthe very notion of concept should be eliminated.

. . . MACHERY ’S ELIMINATIVISM

There may be no other domain in the whole of cognitive sciences as utterly entangledfrom a terminological point of view as that related to concepts. The terms ‘concept’and ‘category’ have been used in a largely unconstrained fashion, leading to confu-sion both terminological and theoretical. Machery () argues that the very term ofconcept should be abandoned, as it does not correspond to anything worthy ofempirical scientific enquiry. This eliminativist conclusion comes as the final pointin his Heterogeneity Hypothesis (Machery : ):

. The best evidence suggests that for each category (for each substance, event,and so on), an individual typically has several concepts.

. Coreferential concepts have very few properties in common. They belong tovery heterogeneous kinds of concept.

. Evidence strongly suggests that prototypes, exemplars, and theories are typic-ally used in distinct cognitive processes.

. The notion of concept ought to be eliminated from the theoretical vocabulary ofpsychology.

Prima facie, the first tenet seems trivial. My dog Izuki can be conceptualized as aCHOW, as a DOG, as a QUADRUPED, as an ANIMAL, and so on and so forth. Thisis not what Machery means, however. Rather, when I conceptualize Izuki as a DOG,I do not have a single unified DOG concept: I have an exemplar-concept of DOG, aprototype-concept of DOG, and a theory-based concept of DOG, each of which maybe used in different occasions, depending on the cognitive process involved. Thus, orso Machery concludes, there is no single notion of concept, and the term should bebanished from psychology.An important starting point in Machery’s reasoning is his repudiation of the

philosophical notion of concept as a component of (propositional) thought. Rather,


he adopts a psychological definition (Machery : ): ‘Concepts are characterizedas being those bodies of knowledge that are stored in long-term memory and that areused by default in the processes underlying most, if not all, higher cognitive compe-tences when these processes result in judgments about the referents of these concepts’.The qualification at the end (‘when these processes result in judgments about thereferents of these concepts’) is important, as it restricts the processes in question to afairly limited range of processes—that is, categorization, concept-learning (forexample, a judgement as to whether Izuki is a dog) and induction (for example, ajudgement to the effect that, given that Izuki is a dog and he barks, then dogs bark).But these are all that concepts are involved in, on a view such as Machery, because hisdefinition is operational: concepts will be those mental entities, whatever they are,that have been identified in empirical psychology as involved in categorization,concept learning, and induction. Given that psychology has come up with threewell-recognized, but largely disjointed, such entities, prototypes, exemplars andtheories, these are concepts, with the consequence that there is no unified conceptfor any category. Hence, the eliminativist conclusion.

Surely, however, this is premature. For one thing, one may disagree with Mach-ery’s definition of concept and point out that it limits the explanatory power of thenotion in a way that makes it difficult to account for thought. While there is certainlya whole host of interesting things to say about categorization, concept-learning, andinduction, there seems to be a large chunk missing from the story: what happenswhen we have acquired the concept and are able to categorize entities correctly? Howdo concepts combine in thoughts and in the semantic interpretation of utterances?What is their role, if any, in deduction? Those questions and quite a few others seemnot only to be missing, but to be wilfully ignored in Machery’s operational defin-ition.10 In addition, it seems that the whole reasoning is askew. The fact that differentbodies of knowledge relative to the same category are used in different cognitiveprocesses is neither surprising, nor unnatural. It is Machery’s definition that entailscalling them all ‘concept’, rather than considering that concepts give access to them,11

that leads to the consequence that the notion of concept is not a unified notion.So, pace Machery, one may want to have a more complete theory of concepts,

of their (semantic) functioning, and of their involvement in mental life. While

10 Indeed, this seems to be implicitly recognized in Machery’s rejection of philosophical criticisms ofpsychological theories of concepts. He points out (rightly) that the psychological theories of concept are notaimed at solving the semantic problems for which philosophical theories of concepts are formulated. This is quitetrue, but basically it leaves us with no story, semantic or otherwise, about the role of concepts in propositionalthought and semantic interpretation.

11 Machery criticizes what he calls ‘hybrid theories of concept’, where a concept is supposed to be amixture of exemplars, prototype, and theory. I will not discuss his criticism here, but note that the proposalgiven here is not hybrid in this sense: it says that concepts are not exemplars, prototypes, or theories, butrather that there is access from concepts to those bodies of knowledge about the corresponding categories,and vice versa.


prototypes, exemplars, and theories have a part to play in the whole picture, conceptscannot be reduced to them. But, if so, what are concepts?

. . . WHAT ARE CONCEPTS?

Here, it is useful to go back to basics. What we are interested in is human thought andits differences or similarities with animal thought. Human thought is productive—that is, just as there seem to be no limits to the contents that can be communicated inlinguistic communication, so there seem to be no limits to the contents that can bethought. As we have seen (see Section ..), productivity in language is linked todiscrete infinity, itself the result of combining discrete units. There is no reason tosuppose that productivity in thought and productivity in language rest on differentmechanisms. This leads to the conclusion that human thought12 is combinatorial,just as human language is. If this is so, then the question is: what are the units that getcombined in thought? And this is where concepts come in. Thus, the definition ofconcepts that I propose (and that is highly different from Machery’s) is that conceptsare the units that are combined in thought.This obviously leads us to the view that there is a Language of Thought, as

advocated by Fodor (, ; Fodor and Pylyshyn ), following medievalphilosophers such as, for example, Ockham (see Panaccio , ). The idea thatthere is a Language of Thought, combinatorial in nature, puts strong constraints onthe nature of the items that are combined—that is, concepts. At a minimum,concepts have to be of such a nature that they can be combined. This may be seenas a syntactic requirement. But, equally, thoughts have contents, and these contents,on a combinatorial view of thought, must be interpretable as the result of semanticcompositionality. And this makes it highly unlikely that concepts can be eitherprototypes, exemplars, or theories.13 We will now discuss each of these in turnrelative to semantic compositionality (the stronger constraint here).

.... Prototypes

Prototype theory was born in the s, largely through the work of Rosch (,, ). It came as a challenge to the so-called Classical Theory of Concepts(which goes back to the classical Greek philosophers, notably Plato), according towhich a concept is a definition that allows humans to categorize things—that is, todecide whether or not they fall under the concept, depending on whether they satisfy

12 This restriction is not intended to deny combinatoriality to animal thought, but I leave this discussionfor another occasion.

13 However, this does not mean that prototypes, exemplars, and theories have nothing to do withconcepts. Rather, concepts are not, pace Machery, prototypes, exemplars, or theories.


the definition or not. The main and most obvious problem with the Classical Theoryis that it is very difficult, if not impossible, to come up with a definition even for themost usual of concepts.14 To take a simple example, it seems impossible to come upwith a definition of such everyday concepts as CAT or DOG.

What is more damaging to the Classical Theory is that it entails that membershipin a category is absolute, rather than relative. This predicts that all members of acategory should be equal (that is, equally members of the category), a prediction thathas been, prima facie, contradicted by empirical evidence. Contrary to the ClassicalTheory’s prediction, when participants have to do a task in which they are asked toevaluate strength of membership in a category, they judge that, for example, a robin isa better member of the category birds15 than is a penguin. What is more, when askedto evaluate the truth of categorical sentences (for example, ‘An elephant is a mam-mal’), their response is quicker for ‘better’ members of a category than for ‘worse’members. For instance, it is quicker to say that the sentence ‘A robin is a bird’ is truethan to say that the sentence ‘A penguin is a bird’ is true. This led Rosch (, ,) to propose Prototype Theory. According to Prototype Theory, objects will beclassified into a category relative to their similarity to a prototype16 (or best exem-plar) of the category. This similarity is itself measured by the number of features thatthe object shares with the prototype. Thus, one would expect a sparrow to be a ‘goodmember’ of the category birds, because it shares most of the features of the prototypeof birds—that is, the robin. By contrast, one would expect an ostrich to be a ‘less goodmember’ of the category bird, because it shares fewer of the features of the prototypeof bird. This, of course, is in keeping with the empirical results described above,though, prima facie, in contradiction with the Classical Theory.

One central question if the prototype of a category is to be construed as theconcept for that category is how stable the prototype (based on typicality judgements,as described) is both between subjects and within subjects. Let me elaborate: withinsubject stability has to do with the stability of the concept for a given individualthrough time; between subjects stability has to do with whether two differentindividuals will agree on what the prototype for a given category—for example,bird—is. These correspond to slightly different worries. Regarding within subjectstability, the worry is whether if, owing to circumstances, an individual’s prototypefor bird changes from, for example, penguin to robin, her initial thoughts about birdsand her latter thoughts about birds have the same object—that is, are they allthoughts about birds? Regarding between subject stability, the worry is whether, if

14 This had, in fact, already been noted in Greek antiquity. When Plato proposed a definition of man asa ‘featherless biped’, Diogenes of Sinope threw a plucked chicken in Plato’s Academy, saying ‘Behold! Thisis a man’. Or so the story goes. But the very fact that it was told at the time shows that the theory was notuniversally accepted even then.

15 Categories are indicated in italics.16 The prototype is thus supposed to be the concept corresponding to the category.


an individual’s prototype for bird is a penguin, while her neighbour’s prototype forbird is a robin, they are thinking about the same thing, or having thoughts aboutobjects belonging to different categories.17 Thus the stability of prototypes is not anunimportant question for a view that claims that concepts are prototypes.Rosch () reported values for between subject agreement of over .—that is,

a very high rate of agreement. However, the statistics used are not without problem,as they are sensitive to sample size—that is, to the number of participants in theexperiment. Using more appropriate methods over the same data, Barsalou ()has found a much lower agreement, i.e., about ..18 Based on a large-scale statisticalanalysis of the results of over twenty groups of subjects, the final estimate is at . (inother words, any subject has a per cent probability of sharing her prototype of, forexample, BIRD with any other subject in the experiment). These studies, notably,included common taxonomic categories (for example, birds). Regarding withinsubject agreement, Barsalou () gives an estimate of about . and notes thatthe variability is much lower for highly typical and highly atypical exemplars than itis for moderately typical exemplars. Thus, within subject agreement is much betterthan between subject agreement, but is still not at ceiling. This is rather problematicfor the view that prototypes are concepts, because it suggests that, while an individualmay be relatively (but not entirely) secure in her conviction that she is thinking aboutbirds on different occasions, she can be much less secure in her conviction that sheand her neighbour are thinking about birds in a given occasion.Machery () has defended prototype stability, though his arguments are less

than convincing. Regarding between subject agreement, he relies only on Rosch’sestimate of ., ignoring Barsalou’s much lower results () without giving anyargument for doing so.19 For within subject agreement, he relies on Barsalou’s results()—that is, an estimate of .—commenting that this is a high correlation.Machery (: ) concludes: ‘there is instability in our judgments about thetypicality of some items, namely those items that are neither typical nor atypical’.However, this is not entirely faithful to what Barsalou himself reports: Barsalou (:) didnot speakof the items that triggeredhighly variable judgements as ‘neither typicalnor atypical’, but spoke of ‘moderately typical’ items.Machery () gives as an exampleheaps: if participants are presented with items that are clearly heaps, items that are clearlynot heaps, and items that are borderline, one would expect indeed that the borderline

17 These questions are linked to systematicity, the fact that the ability to think some thoughts dependson the ability to think other thoughts, because the units composing them are identical (see Fodor andPylyshyn , and Section ...).

18 Barsalou () gives a general discussion of the stability of graded assessment of categories (i.e., ofprototypes). References to more specific studies are found in his paper.

19 This is all the more surprising in light of the fact that for within subject agreement he uses Barsalou’sdata. Both are presented in the same paper, so it is hard to understand why he should ignore the betweensubject data given by Barsalou while using his within subject data.


items will be classified as sometimes heaps and sometimes not heaps, even when theclassification isdoneby the samesubject.Thus, ‘some judgments aboutheaps areunstable’(Machery : ), and typicality judgements reflect that instability. There are twoimportant problems with that argument. The first is that Machery seems to misunder-stand thenatureof the task: participants arenot asked to judgewhether somethingbelongsor does not belong to a given category, but, on the understanding that it does, to judge howgood amember of the category it is on a scale ofmembership.Here, it is important to notethat Barsalou, for those items most subject to variation, spoke of ‘moderately typical’items, not of ‘neither typical nor atypical’ items. If anything, moderately typical itemsshould bemore easily judged to belong to the category than atypical items. However (andthis is what the task Barsalou used showed), it may be more difficult to judge formoderately typical items whether they are highly typical or highly atypical (for instance,no one would deny that a toucan is a bird, but is it a typical bird?). Finally, and this isthe second problem, Barsalou (: ) notes that ‘there were also sizeable changesin the typicality of both highly typical and atypical items’.

In sum, it is mildly doubtful that a subject can be attributed a thought about thesame category from one occasion to the other and it is highly doubtful that twosubjects on a given occasion have thoughts about the same category, because it is notclear that they share the corresponding prototype.

There is an additional problem for the view that prototypes are concepts, and thisproblem lies in compositionality. As we have seen (see Section ..), if concepts arethe units of thoughts, given both the combinatoriality of thoughts and the fact thatthoughts have contents, they have to be susceptible of semantic compositionality.Fodor () has given the classical argument. He notes that, according to PrototypeTheory, falling under a concept is tantamount to being similar to the (corresponding)category prototype. Thus compositionality in prototype theory should be defined asfollows (Fodor : ): ‘A thing’s similarity to the exemplar [the prototype] of acomplex concept is determined by its similarity to the exemplars [the prototypes] ofits constituents’. However, as Fodor notes, this does not seem to be the case. Forinstance, a goldfish is a good example (and may well be the prototype) of PET FISH,but it is not a good example of FISH (a salmon would do much better) and neither isit a good example of PET (a cat or a dog would be a much better example). A possibleobjection is that a prototype should be seen as a set of features rather than as the bestinstance of a category. If this is the case, then compositionality between prototypes ina given complex concept should have to do with the combination of the features ofthe constituent concepts. Here, Fodor turns to Smith and Oshershon’s proposal ().A prototype is a matrix of weighted features (the weight of each feature depends on theprobability that any object falling under the concept has the feature20). Complex

20 In other words, the features are statistical rather than definitory.


concepts correspond to a new feature matrix derived from the feature matrices of theirconstituents. Fodor takes the example of PURPLE APPLE. The prototypical apple isred (though, obviously, some apples can also be yellow or green, and so on). ThusAPPLE has a feature RED. To get PURPLE APPLE, the RED feature has to bereplaced by a PURPLE feature, and the weight of that PURPLE feature has tobe suitably increased. This is because RED is a statistical feature of APPLE, but nota universal feature of APPLE. But, while being red is only true of some apples, beingpurple is true of all purple apples. In Fodor’s terms, purple apples being purple is alogical truth. So the question is what is a ‘suitable increase’ when the colour feature ofAPPLE is changed from RED to PURPLE in the complex feature matrix for PURPLEAPPLE? As Fodor points out, there is no simple answer to that question. A possibilityis to treat the logical truth—that is, the fact that all purple apples are purple, as anextreme case of a statistically reliable truth. Another possibility is to admit thatweight feature is not compositional. Neither of these possibilities is satisfying.Fodor identifies the root of the problem as the fact that, in such a case, the weightof the feature PURPLE in PURPLE APPLE is determined not by the prototype, butby the logical form of the complex concept PURPLE APPLE. Given that prototypesdo not have logical form, it is out of reach of prototype theory.Fodor () discusses yet another attempt at prototype compositionality. Kamp

and Partee () propose that in a complex concept—for example, STRIPEDAPPLE—the modifier (here STRIPED) should be evaluated not relative to itswhole set (here the category of striped objects, from tigers to apples), but relative toapples—that is, relative to those apples that are striped. Thus a typical striped apple isnot typical of STRIPED (things), but is typical relative to apples that are striped. This,as Fodor notes, corresponds to a recalibration of the concept STRIPED. But this‘solution’ begs the problem in as much as identifying the relevant reference set for acomplex concept (for example, APPLE for STRIPED APPLE) depends on a previousunderstanding of the compositional structure of that complex concept.The general conclusion is that, while there may be and often are prototypes for

complex concepts (for example, goldfish for PET FISH), these prototypes are not theresult of compositionality. Here there are two solutions, a bad one and a good one.One could bite the bullet and accept that prototypes are indeed not compositional,but claim that complex concepts are not compositional either: rather they are to beunderstood on a par with idioms in natural language. Although ‘to kick the bucket’means ‘to die’, this meaning is not accessible through the sheer semantic compositionof the items in ‘kick the bucket’. There is one major problem with that proposal,which is that it ignores the logical truths that derive from complex concepts. Anobject falling under BROWN COW has to be a cow and be brown because BROWNCOW is composed of BROWN and COW (and additionally none of these two‘features’ is optional to any degree: both are necessary). Obviously, this is thebad solution. The good solution lies, again, in accepting that prototypes do not


compose, and in claiming that prototypes are not concepts. They are not concepts,because prototypes for complex concepts are not the result of the composition of theprototypes for their constituents. Rather they are the results of the computation bysemantic compositionality of the complex concept and accessing, for example, theprototype goldfish as the most typical of the objects in the category pet fish. Moreover,and this is the second reason why prototypes are not concepts, prototypes for simpleconcepts—for example, prototypes for PET and for FISH—cannot combine into thecomplex concept PET FISH.

.... Exemplars

The Exemplar Theory of Concepts (first proposed by Brooks and Medin andSchaffer ) proposes that a concept is a set of exemplars. An exemplar is knowledgerelative to a particular member of the corresponding category. The classification of newitems is based on a comparison with existing exemplars of the concept, based onanalogical reasoning—that is, on similarity. There are different models of exemplars,some featural, others dimensional. A main difference between Exemplar Theory andPrototype Theory is that the first supposes that information about many categorymembers is stored, while the second supposes that a prototype is built. In other words,there is a form of abstraction involved in Prototype Theory that is absent fromExemplarTheory. This has direct consequences on the two factorswe examined above—that is, thestability of concepts within and between subjects and the compositionality of concepts.

Let me begin with the stability of concepts between subjects. Clearly, if conceptsare exemplars, there is good reason to think that concepts are different betweensubjects: two different individuals living in different environments will have haddifferent experiences of particular members of the same category, and have, as aconsequence, different exemplars. Thus, if concepts are exemplars, two differentindividuals, barring very specific circumstances, will have different concepts.21

Regarding within subject stability, Exemplar Theory does not fare much better:clearly, as the subject experiences more and more particular members of a givencategory, she will add more and more exemplars, thereby changing her correspond-ing concept. So, to sum up, on Exemplar Theory, an individual cannot be sure thather BIRD thought on a given occasion and her BIRD thought on another occasionbear on the same object. What is more, she cannot be sure that her BIRD thought andher neighbour’s BIRD thought are about the same set of objects.

What about compositionality? Do concepts compose on Exemplar Theory? It isimportant to remember here that, on Exemplar Theory, concepts are sets of

21 It is noteworthy here that all experiments testing Exemplar Theory have used artificial categories (seeMachery ), which makes this consequence of Exemplar Theory less salient, as every participant hasexactly the same experiences. But when natural categories are concerned in everyday cognition, conceptinstability between subjects is a problem.


exemplars. How sets of exemplars can combine is a moot question. One obvioussuggestion is that the complex concept PET FISH could be the set of exemplars in theintersection of the set of exemplars for the concept PET and the set of exemplars forthe concept FISH. Apart from the fact that it is subject to difficulties relative toindividuals who do not have exemplars for fishes in their PET concept,22 this solutionis subject to very much the same objection as has been given to the solution proposedby Kamp and Partee () for prototype compositionality. It begs the question bypresupposing what has to be explained—that is, how compositionality proceedswhen it has to work with exemplars. Thus Exemplar Theory does not fare muchbetter than Prototype Theory as a theory of concepts.

.... Theories

The Theory Theory of Concepts was developed in the s by Carey () andMurphy and Medin (). Murphy and Medin, just as Prototype theorists andExemplar theorists, were mainly interested in categorization and concept learning.Carey, as a developmental psychologist, was interested in concept change. Accordingto Machery (), there are two ways in which the Theory Theory has beenconceived: either as the idea that concepts are theories or as the idea that conceptsare elements of theories. On the first view, concepts store knowledge that is fairlysimilar to a scientific theory, construed functionally as explanatory. Thus the know-ledge stored under a given concept explains the properties of the members of thecorresponding category. As Machery (: ) points out, on such an understand-ing, ‘a theoretical concept is supposed to store some nomological, causal, functional,and/or generic knowledge about the members of its extension’. On the second view,according to which, rather than being theories, concepts are elements of theories—concepts are structured by theories about the world. This brings us back to the ideaof conceptual domains (see Section .). Entities in the same domain (for example,folk-biology) are treated in a similar way, or, in other words, our ways of reasoningabout them are constrained by the domain to which they belong. Hence, the type ofknowledge stored by concepts in a given domain will be of a similar kind. This isbecause a domain is constituted by a specific body of general knowledge, whichinfluences the more specific information stored in the different concepts that belongto this domain.By contrast with Prototype and Exemplar theorists (who rely on general similarity-

based cognitive processes), Theory theorists have been relatively less explicit as to thecognitive mechanisms involved (though see Gopnik et al. for a Bayesianaccount of learning causal relations and Gopnik and Schultz for more extensive

22 Saying that the concept PET FISH is empty in such cases does not seem an attractive option.


discussions). They have been more interested in challenging similarity-based modelsof categorization.

One interesting question that Theory Theory raises (but that does not arise forPrototype and Exemplar theories) on the view according to which concepts areelements of theories falling under domains that are themselves organized by generalknowledge is what this general knowledge is exactly and where it comes from.Gopnik and Meltzoff () and Carey () have given slightly different answersto this question, though both acknowledge that this general knowledge is largelyinnate. The difference lies rather in its nature. According to Gopnik and hercolleagues, it manifests itself through innate cognitive biases that make some featuresor events salient to the perceiver. According to Carey, this general knowledgecorresponds to innate general principles that are subject to maturation but thatconstrain reasoning even in infants. For instance, infants’ reasoning about objectsseems to be constrained by general principles such as object persistence despiteocclusion, the impossibility for two different objects to occupy the same spatio-temporal location, the necessity, when an object moves, that all its parts move atthe same time, and so on.23 It is important to note that these principles aresubpersonal and do not correspond to occurrent beliefs. Rather, in Carey’s words(: ), they correspond to ‘constraints on the processes that create the repre-sentations of ongoing events’. These processes are modular, and one might surmise,given Fodor’s proposal () on the modularity of mind, that they are informa-tionally encapsulated—that is, that no explicit information can influence them. Onestrong argument for the innateness of this core knowledge is that it has beenevidenced not only in infants, but also in other species, notably but not only otherprimate species.

One not unimportant question is whether Machery () is right in his under-standing of the two versions of Theory Theory. According to him, in the first version,concepts are theories, while in the second concepts are elements of theories (that is,they are ‘organized’ by theories). One may wonder whether Machery’s understandingof the two versions is quite correct as it stands and whether it should not be nuancedsomewhat. On both versions, concepts store knowledge. On the second version, theknowledge stored in a concept depends on the domain to which this concept belongs,as the general knowledge linked to the domain will constrain the representationsbuilt from experiences of members of the corresponding category. Yet, on bothversions, concepts store knowledge (and whether that knowledge is worthy ofbeing called a theory, let alone a theory that bears some resemblance to a scientifictheory, is debatable, despite the claims made by supporters of the first version). Themain difference appears to be that, on the first version, there is no obvious constraint

23 Very much the same principles constrain reasoning about objects in adults (see Section ..).


on the knowledge stored in a concept, while, on the second version, there is. As weshall now see, this difference has some consequences on between and within subjectstability, if not on compositionality.Let me now go to between and within subject stability and to compositionality in

Theory Theory. Here, things are, prima facie, slightly different depending on theversion of Theory Theory one focuses on. If we choose to interpret Theory Theory asthe view that concepts are theories, only weakly constrained by domains (throughperceptual biases), then, unless one is ready to claim that concepts (that is, theories)are innate (and no one is ready to do that), it seems fairly obvious that within subjectstability is out of the question. When the knowledge stored in a concept changes, thenthe concept changes. In other words, within subject conceptual stability is dependenton whether the subject, who has a FISH thought on a given occasion, has hadoccasion to change her theory about fishes, based on new experiences, betweenthat first occasion and another latter occasion on which she entertains anotherFISH thought.24 If she has, then her first FISH thought and her second FISH thoughtdo not make use of the same concept. This should not be surprising: the very ideabehind Theory Theory on that interpretation is that change in theory is conceptualchange. So what about between subject stability on that version of Theory Theory? Itmeets with very much the same problems as within subject stability. If a subject has aFISH thought using a FISH concept that does not include oviparity, while herneighbour has a FISH thought using a FISH concept that does, then their thoughtsuse two different concepts, which, on a view in which concepts determine extensions,may not be about the same objects.On the second version of Theory Theory, where concepts store knowledge

accessed under domanial constraints, things are slightly different. This is because,as already indicated, the knowledge that is stored in a concept is constrained bydomanial knowledge, which should somewhat limit variability. Yet, in that secondversion as well as in the first, the knowledge stored into a concept is subject to changebased on experience. What is more, the domanial knowledge itself is subject tomaturation (it becomes gradually accessible), leading to changes in conceptualknowledge and hence to conceptual change. Thus, again, within subject stability isfar from being ensured. What about between subject stability? There, domanialconstraints should limit variation, provided that subjects are more or less of an age(that is, that their respective domanial knowledge have reached the same stage ofmaturation). However, it is not enough completely to eliminate variation, given thatconceptual knowledge is still subject to experience, making it unlikely that conceptswill be identical between two different individuals, even if they have identical

24 Suppose, for instance, that she has learnt that fishes are oviparous; presumably, on the first occasiondolphins and cetaceans would be included in her fish category, while they would not be on the secondoccasion.


domanial knowledge. So, on the Theory Theory of Concepts, within and betweensubject stability cannot be guaranteed.

What about compositionality? It is not entirely clear how bodies of knowledge,such as concepts are supposed to be in the Theory Theory of Concepts, can compose(and here there is no difference between the two versions of the Theory Theory). Aswe saw relative to Prototype theory (see Section ...), one test of the ability of atheory of concepts to deal with conceptual compositionality is its ability to accom-modate logical truths—that is, truths that are entailed by the composition of theconstituents of a complex concept. The example given (following Fodor ) wasPURPLE APPLE. The basic problem was how the fact that purple apples are purple as amatter of logical truth can be accommodated in a given theory of concept, here theTheory Theory of Concept. The main question, as we saw relative to Prototype theory,has to dowith the status of the information in the concept. Regarding Prototype Theory,the problem was that features are statistical, making it difficult to give logical truth itsdue. So what is the status of the knowledge stored in concepts in the Theory Theory ofConcepts? Here, we should not be misled by the term ‘knowledge’, which presupposestruth. This cannot be the case for the information stored in concepts in Theory Theory.The comparison with scientific theories strongly suggests that the information stored inthe concept has the status of revisable assumptions, not the status of ‘true knowledge’,otherwise they could not be subject to revision, which they obviously are.

So suppose that we have to account for the complex concept PURPLE APPLE inTheory Theory. Clearly we will have to change the concept APPLE to indicate thatpurple apples are purple and that it cannot be otherwise. The first step, as was thecase for Prototype Theory, is unproblematic. We replace the information relative tothe colours apples can have in the concept APPLE by the information that purpleapples are purple. The next step is less straightforward. How can we indicate that thestatus of PURPLE APPLES ARE PURPLE is that of a logical truth? Or, to say itotherwise, how can we indicate that this information is not an assumption subject torevision, but a necessary truth (that is, there is no possible word at which purpleapples are not purple)? On the face of it, there are two apparent solutions to thatdilemma. The first one is to say that the information that PURPLE APPLES AREPURPLE is a truism and could never be false. But this begs the question by, onceagain, presupposing compositionality solved, while what is needed is to give anaccount of it. The second solution is to give the information that PURPLE APPLESARE PURPLE the status, not of an assumption, but of a logical truth in the complexconcept PURPLE APPLE. However, again, it is not clear that this does not amount tobegging the question. How do we know that the information purple apples are purpleis a logical truth if not through the fact that the complex concept PURPLE APPLE isthe result of the semantic composition of the two constituent concepts PURPLE andAPPLE? There is a second problem: on Theory Theory, concepts are stores ofknowledge, theories on a par with scientific theories. This suggests that complex


concepts as well are stores of knowledge on a par with scientific theories, in whichcase the information that they gather are assumptions and not logical truths.Thus, Theory Theory does not fare any better than Prototype Theory and Exem-

plar Theory as far as within and between subject stability, as well as semanticcompositionality are concerned.

.... The Neo-Empiricist Theory of Concept

According to Machery (: ), one can isolate two main tenets of Neo-Empiricism (see, e.g., Barsalou ; Prinz ) relative to concepts:

. The knowledge that is stored in a concept is encoded in several perceptualrepresentational formats.

. Conceptual processing involves re-enacting some perceptual states andmanipulating these perceptual states.

As Machery points out, the first tenet contrasts with the view that conceptualknowledge is amodal—that is, encoded in a language-like format distinct from percep-tual representations. While the first tenet goes back to the classical British empiricists(notably Locke and Hume), there is a distinctly modern flavour to the second, having todo with the currently popular notions of embodied cognition and simulation. On theNeo-Empiricist view, we can compose re-enacted or simulated percepts to build newperceptual representations.Neo-Empiricists reject twonotions that are central to classicalEmpiricism: pictorialism (the view that concepts—or ideas, in empiricist terminology—are picture-like) and associationism (the view that cognitive processes are based onassociations owing to spatio-temporal contiguity). As a matter of fact, Neo-Empiricismsees cognitive processes as computational in nature and accepts a degree of nativism.Machery () has convincingly argued that there is no uncontroversial empirical

evidence in favour of the two tenets of the Neo-Empiricist Theory of Concepts.Beyond the lack of empirical evidence in its favour, how does the Neo-EmpiricistTheory fare relative to between and within subject stability and to compositionality?On the Neo-Empiricist Theory of Concepts, the content of a concept depends on theexperiences of the subject. To cut a long story short (for parallel arguments, seeSections ... and ...), given this dependence, there can be neither within norbetween subject stability. Regarding compositionality, as said above, Neo-Empiricismproposes that perceptual representations can compose. If this is the case, it wouldseem that some complex concepts, such as, for example, PURPLE APPLE, can beaccounted for, though it is not clear that the corresponding logical truth could be(perceptual representations are not truth evaluable). But what about other complexconcepts—for instance, PET FISH? Short of having had experience with aquariums(and in this case, compositionality is not really involved), how could one composeperceptual representations of pets and perceptual representations of fishes?


Thus, in addition to lacking unequivocal empirical support, it appears that Neo-Empiricism does not ensure conceptual stability and cannot really account forcompositionality.

.... Conclusion

Thus, it seems that, pace Machery, neither prototypes, exemplars, nor theories areconcepts, though obviously they do have something to tell us about some of thecognitive processes in which concepts are involved, as we shall see (Section ..). Solet us turn to what concepts are.

. . . WHAT CONCEPTS ARE

I will now turn to what concepts actually are, using some of the conclusions that canbe drawn from what they are not. Thus we will begin by highlighting what can bedrawn from the examination of Prototype, Exemplar, Theory, and Neo-Empiricisttheories of concepts.

.... Taking stock

I would like to come back to the link between conceptual stability (both between andwithin subject) and compositionality. The importance of conceptual stability isdirectly linked to what Fodor and Pylyshyn () call systematicity. Systematicitycorresponds to the fact that the ability to entertain certain thoughts (for example, thethought that John loves Mary) is intrinsically connected to the ability to entertainother thoughts (for example, the thought that Mary loves John).25 Systematicityentails that the constituents of the thoughts (that is, concepts) make the samecontribution on each occasion of their occurrence. The link between systematicityand semantic compositionality is that semantic compositionality is possible only ifsystematicity is the case, and compositionality is what allows us to distinguishbetween two thoughts that have the same components (for example, MARYLOVES JOHN and JOHN LOVES MARY) and different logical forms (given thatcompositionality, as we have seen, determines logical form). Thus, it is unlikely thatany account of concepts that makes systematicity impossible will allow composition-ality.26 And as Fodor points out, compositionality is non-negotiable if we want toaccount for the productivity of thought. This suggests that theories of conceptsshould be constrained by semantic worries rather than by worries about

25 Mutatis mutandis, the same goes for language, as we shall see in Chapter .26 This is exactly what we found out in our examination of Prototype, Exemplar, Theory, andNeo-Empiricist

theories , (see Sections ...–...).


categorization and concept learning. Note that this does not mean that there isnothing to say about categorization and concept learning (indeed, I will have muchto say about both—see Section ..). But it does mean that the main constraint onthe nature of concepts is semantic. Concepts have to be such that they are stable bothbetween and within subjects (systematic) and they have to compose semantically.27

The accounts of concepts thatwehave examined failed both systematicity (conceptualstability) and semantic compositionality. Despite their differences, they all share thesame characteristics: they see concepts as storing information (features, best instances,exemplars, theories), and, in all cases, the information stored depends on the subject’sexperiences. This and the preceding considerations suggest a few conclusions:

• Any theory of concepts can accommodate logical truths only if it can handlesemantic compositionality.28

• Any theory of concepts that can handle semantic compositionality has to allowfor systematicity.

• Any theory that sees concepts as stores of information (whether this informationhas to do with features, best instances, exemplars, theories, or perceptualrepresentations) can allow for systematicity iff (if and only if) all the items ofinformation in concepts are taken to be innate (which has the unhappy conse-quence that one cannot accumulate knowledge about the objects in the corres-ponding categories). Otherwise, conceptual stability (and hence systematicity) isnot ensured.

• Any theory that sees concepts as stores of information (whether this informationhas to do with features, best instances, exemplars, theories, or perceptual repre-sentations) can accommodate logical truths iff (if and only if) all the items ofinformation in concepts are taken to be necessary truths (which is nonsensical).

• All of this should be seen as a reductio ad absurdum of the view that conceptsstore information.

A general conclusion is that simple concepts (for example, BROWN or COWversus BROWN COW) cannot be stores of information nor can they depend onexperience. As Fodor has often remarked, this means that the metaphysics ofconcepts (roughly what concepts are) cannot depend on the epistemology of con-cepts. This corresponds to a general principle, according to Fodor (: ): ‘Idisapprove, as a matter of principle, of attempts to draw ontological conclusions fromepistemic premises. The right direction of argument is the other way around’. So letus now see where this principle (let us call it Fodor’s Principle) leads us.

27 This was implicitly recognized by Machery (), as he was at pain to argue (unconvincingly, as wesaw, see Section ...) that prototypes do satisfy that constraint.

28 This comes back to Fodor’s remark (see Section ...) that logical truths are a matter of logical formand the logical form of the concept can be accessed only through semantic compositionality.


.... Conceptual atomism

As we have seen, the constraints on the nature of concepts (a metaphysical question)have to be semantic rather than epistemological. Concepts are to be such as to allowsemantic compositionality and systematicity. Additionally, given that concepts—most of them at least, clearly the concept UNICORN does not and neither, presum-ably, does the concept AND, but CAT, DOG, and so on do—correspond to sets ofobjects in the world, concepts should also connect, in one way or another, with thesesets of objects in the world—that is, with the categories corresponding to them. Insemantics, there are two ways of securing this connection: it can be done eitherintensionally or extensionally. On an intensional view of the relation between theconcept and the corresponding category, the intension of the concept specifiesthe condition(s) that objects, events, or substances have to satisfy to fall into thecorresponding category—that is, the intension of WATER is (informally) any sub-stance that has the chemical composition HO (or, more simply, HO). In otherwords, the intension of a concept is something like a definition. As we have seen (seeSection ...), any view on which concepts are definitions is epistemologicallyunlikely. However, on Fodor’s Principle, we should not let epistemological concernsdictate our metaphysics. This takes care of that objection. How would an intensionalview of concepts fare regarding systematicity and compositionality? Quite well, as amatter of fact: if concepts are intensions in a metaphysical and non-epistemologicalsense (that is, the intension of the concept is independent of the subject’s mentalstates, and notably of her beliefs), there is a single intension for each concept, andintensions, being semantic entities, compose.

On an extensional view of concepts, concepts are extensions, or, less brutally, referdirectly to their extensions. In other words, WATER directly refers to water. Again,both systematicity (no matter how much a subject’s view of water may change, herconcept WATER still directly refers to water, whatever her beliefs about water—forexample, whether she knows or does not know that water is HO) and composition-ality are ensured. Thus, on the basis of semantics alone, there does not seem to be anyreason to prefer the intensional account of concepts over the extensional account orvice versa. Fodor, since The Language of Thought (), has insisted that conceptsare extensional, because his goal is to naturalize the mind.29 Following in Dretske’sfootsteps (), Fodor roots his naturalism in a staunch externalism, according towhich representations can be naturalized only to the extent that they are extensionaland not intensional. Another way of putting it is that it is more difficult to followFodor’s principle on an intensional account than on an extensional account, as weshall now see.

29 As we saw in Section .., this was also Millikan’s goal, though she was dealing with communicationrather than with thought.


Let me approach the matter through a by now classical Thought Experiment,Putnam’s Twin Earth (). I will simplify the scenario somewhat, keeping only theingredients that are relevant to my argument and transposing it from language tothought. Putnam asks his reader to imagine that, in addition to the Earth, there is aTwin Earth, which is identical molecule per molecule to the Earth, but for onedifference: on Twin Earth, what passes for water (that is, a drinkable, odourless,savourless, colourless liquid substance that quenches thirst) has not the chemicalcomposition HO, but the chemical composition XYZ (let’s call this XYZ liquid‘twater’). Given that Earth and Twin Earth are identical molecule per molecule, eachindividual on Earth has a twin counterpart on Twin Earth, and, given a modicum ofLaplacian determinism combined with a materialist view of the mind, when anindividual has a thought on Earth her twin has a (type-)identical thought on TwinEarth. So take Earthian Hannah and her twin counterpart on Twin Earth,TWHannah. Suppose that Hannah thinks WATER QUENCHES THIRST. Then,TWHannah simultaneously thinks WATER QUENCHES THIRST. Now supposethat Hannah and TWHannah are absolutely ignorant of the chemical composition ofwater and twater. The question is whether Hannah and TWHannah share the samethought or not. Any solution will have to consider the contributions their respectiveconcept WATER makes to their respective thoughts. On an epistemological versionof the intensional view of concepts, it would seem that Hannah and TWHannahshare the same thought, despite the fact that what Hannah’s concept WATER targets(its extension) is water and what TWHannah’s concept WATER targets (its exten-sion) is twater.30 Thus, on this view, they share the same thought-type, even thoughtheir respective thought tokens do not have the same object, a rather unfortunateresult. There is an alternative view of what happens on the epistemological version ofthe intensional view of concepts. One could argue that, on an epistemological view ofintensions, Hannah’s and TWHannah’s WATER concept (which they share as theyshare the corresponding intension) refers to both water and twater. In other words, asingle intension would cover two distinct extensions. It would be tantamount to whatwould happen to someone who believes that a fish is an animal that has fins, swims,and spends its whole life in water. Presumably, this individual would consider thatdolphins and cetaceans are fishes, on a par with salmons, pikes, and sharks. On sucha view, on the day this individual somehow discovers that fishes are oviparous andnot mammals, her concept changes in tandem with its intension that has beenmodified. Note that, on that interpretation, the epistemological version of theintensional view of concepts basically comes to grief on the same counts as theTheory Theory (see Section ...)—that is, it does not accommodate systematicityand hence semantic compositionality.

30 This was actually Putnam’s conclusion (). For different views, see, e.g., Bilgrami (); Burge().


On an extensional view of concept, Hannah and TWHannah do not share thesame thought, because they do not share the concept WATER, given the difference inextension between Hannah’s concept WATER and TWHannah’s conceptWATER. Indeed, it would make sense to distinguish them by, for example, indicesin such a way that it is clear that it is not the same concept that occurs in Hannah’sthought and in TWHannah’s thought. Thus, Hanna thinks WATER QUENCHESTHIRST, while TWHannah thinks WATER QUENCHES THIRST.

On the face of it, the difficulties relative to the intensional view noted are hardlydecisive objections against the intensional view of concepts, because, on the meta-physical version of the intensional view,31 Hannah and TWHannah do not share thesame concept: the intension of Hanna’s concept is roughly SUBSTANCE THATHASTHE CHEMICALCOMPOSITIONHO, while the intension of TWHannah’s concept isroughly SUBSTANCETHATHAS THECHEMICALCOMPOSITIONXYZ (rememberthat on themetaphysical view intensions are independent of subjects’ beliefs and epistemicstates). Having different intensions, the respective WATER concepts of Hannah andTWHannah will lead to different extensions. In effect, they just have different concepts.

There is still a problem, however, which is that, even though we want to respectFodor’s Principle, we also want to be able to supplement the metaphysic view ofconcepts with an epistemic view of concepts that will allow us to say how humansactually use concepts in categorization, and so on. Though this may not be impos-sible on an intensional view, it would be a task fraught with difficulties. Intensionsare suspiciously like definitions, and definitions, as discussed (see Section ...),supposing that they exist, do not seem to be readily accessible to consciousness.Nevertheless, in epistemology, definitions have to be applied by someone in order todetermine the set of objects that satisfies them, and that seems to presuppose somekind of knowledge, conscious or not. But, on a metaphysical version of the inten-sional view of concepts, it is difficult to imagine how such knowledge would comeabout. It would seem extremely implausible that, for example, knowledge of theintension SUBSTANCE THAT HAS THE CHEMICAL COMPOSITION HO forthe conceptWATER is innate, and would have been known even before the discoveryof the chemical composition of water.

On the other hand, an extensional view of concepts does not imply any kind ofknowledge on the part of the possessor of the concept, as, on that view, concepts haveno other content than their extensions. Though there is plenty to know or discoverabout their extensions (the objects in the corresponding categories), there is nothingto know about the concepts themselves, leaving the field wide open to complemen-tary epistemological accounts. Thus, one does not need to buy into Fodor’s naturalistagenda to prefer an extensional characterization of the nature of concepts.One important consequence of such a characterization is that, barring semantic

31 And that is the only version compatible with Fodor’s Principle.


compositionality (that can occur only in complex concepts), concepts are atomic:having no content besides their extension, they cannot be decomposed. This, as weshall now see, is a rather nice consequence of the extensional view.Indeed, as has been pointed out by both Fodor (, , ; Fodor

and Pylyshyn ) and Millikan () though with slightly different arguments,all concepts cannot be complex—that is, susceptible of decomposition into compo-nent parts. Fodor’s argument is to the effect that, if all concepts were complex, thenthe conceptual apparatus would be closed on itself and concepts would be devoid ofcontent. In Fodor’s colourful expression, ‘the buck has to stop somewhere’: in otherwords, there can be complex composite concepts (for example, BROWN COW) onlyif there are primitive concepts (for example, BROWN, COW), concepts of which thecomplex concepts are built. And these primitive concepts are atomic, giving access,not to other concepts, but to the objects in the corresponding categories. Thus, theexistence of primitive concepts is a necessary condition for complex concepts to havecontent. Millikan’s argument is even simpler: she points out that concepts cannot allbe complex, because, to accumulate knowledge about the objects in the correspond-ing categories, one already has to be able to identify objects as falling under theconcepts in question. In other words, concepts are not stores of knowledge; they aremeans to acquire knowledge. It is important that, in contrast with Fodor’s view,Millikan claims that a concept corresponds to an ability to identify the objects in thecorresponding category.32 However, note that Millikan’s objection does not rest onthis epistemological view of the nature of primitive concepts: even on an extensionalview à la Fodor, Millikan’s argument would stand. So, the conclusion is that there hasto be primitive, atomic, concepts. The atomicity of concepts has the nice consequencethat having a given concept is independent of what other concepts one has: in otherwords, a young child can have the concept DOG without having the conceptsMAMMAL, CARNIVOROUS, BARK, and so on.Granted that primitive concepts have to be there if we are to have complex

concepts, the question then is how one determines whether a concept is primitiveor not. Fodor has advocated the idea that concepts are primitive when they corres-pond to a simple (versus complex) lexical item: that is, a single word (rather than acomposite expression) is an indication that the corresponding concept is primitive.The problem with that proposal is that it presupposes a one-to-one correspondencebetween primitive (atomic) concepts and non-decomposable lexical items.33 This isimplausible. To take one of Fodor’s favourite examples, DOORKNOB, this conceptcorresponds to a single lexical item34 in English. But in French it is expressed by the

32 In other words, Millikan has an epistemological view of the nature of concepts, in contravention ofFodor’s Principle.

33 I am ignoring constructive morphology here. It has no impact on the conclusion.34 Though whether that specific lexical item is not linguistically decomposable seems highly debatable.


complex expression poignée de porte. Should we conclude that the concept DOOR-KNOB is primitive for English speakers, but not for French speakers? This wouldcontradict one of Fodor’s central theses, which is the asymmetrical dependence oflanguage on thought, and hence of the lexicon on concepts.35 Another problem withFodor’s suggestion is that, depending on the language, some concepts will belexicalized while others are not: for instance, the colour lexicon is notoriously variablefrom one language to the next, but this does not mean that speakers of a languagesuch as Gaelic, which has a single word for both blue and green, are unable todiscriminate between the two hues (more about this in Section ...). Anotherexample is the term ‘sibling’, which does not exist in French, although Frenchpeople are perfectly able to entertain the concept SIBLING. In other words,concepts are not dependent on language either for atomicity or for existence.Again, this is in keeping with Fodor’s view on the semantic primacy of thoughtover language. So, there does not seem to be any simple answer to how we knowthat a concept is primitive or complex. In conclusion, though, how we determinewhether a concept is primitive is an open question, whether there are primitiveconcepts is not in question.

Let me now say a few words about concept possession (what it is to have aconcept). Admitted that simple concepts are atomic and that complex concepts arecomposed from these primitives, it is only simple concepts that are relevant to what itis to possess a concept (the possession of a complex concept reduces to the possessionof its constituent primitives and semantic compositionality). As we have seen,Millikan conceives of concept possession as the ability to categorize the correspond-ing objects, a view that is unacceptable for Fodor. So what is Fodor’s notion ofconcept possession? Quite simply, and in keeping with the view that concepts are theconstituents of thought, possession of a concept according to Fodor corresponds tothe ability to use the concept in thought. In other words, an individual possesses theconcept COW if she can think a thought using the concept—for example, THE COWIS GRAZING.

So, to conclude, concepts are extensional (their contents are exhausted by theirextensions36), and possession of a concept lies in being able to think thoughtsinvolving this concept. This is the metaphysical story about the nature of conceptsand about what concept possession is. It leaves the field wide open as to what anepistemic account of concepts would be.

35 In other words, in keeping with Fodor’s view, there is no difficulty in considering that DOORKNOBis a primitive concept, and this is the case despite the fact that it is expressed by a composite linguisticexpression in French. Neither French nor English is diagnostic of concept primitivehood.

36 I will come back to concepts corresponding to logical words. Concepts corresponding to fictionalobjects (in keeping with Fodor’s treatment) will be treated as complex concepts.


. . . THE EPISTEMIC STORY

.... Introduction

Granted that having concepts is being able to use them in thoughts rather than beingable to categorize objects, how do we acquire concepts? Before I examine thisquestion, I would like to say a few words about why there are good reasons tothink that human concept acquisition is rather phenomenal. These reasons, as wewill now see, have to do with the size of the lexicon that humans master in the courseof their lives.Estimates of vocabulary size in humans (see Bloom , and the references

therein) are the following:

• -year-old: , words;• high school graduate (c. years of age): ,–, words.

Considering that children produce their first words at around months, this israther stupendous. And, of course, word learning goes on throughout life, so the finalvocabulary is presumably much larger. By contrast, the extent of the vocabularyanimals can master is much more limited (around – words at the most—seeAnderson ). The question I am presently interested in is why this should be so.First of all, let me be clear about what I mean by animal vocabularies. Importantly,

I do not mean the number of signals that a given species has in its natural commu-nication system. The inventory is usually limited to around thirty different signals atthe most (see Anderson , as well as Hauser ; Maynard Smith and Harper). It would be unfair to infer from this rather dismally small communicativeinventory that animal conceptual apparatuses are similarly limited. Rather, animalsmay have large conceptual apparatuses, but be limited in the number of their signalsby the holistic nature of these signals owing to the error limit (see Nowak et al. ,and Section ..). So natural animal communication systems may not be goodguides to animal conceptual apparatuses.But, while natural animal communication systems may be limited by the holism of

their signals, there is no reason to think that this is the case of the ‘languages’37 thatanimals participating in so-called animal language studies are taught. These animalswere mainly apes (chimpanzees, bonobos, and one gorilla), though dolphins and greyparrots were also involved. The teaching was mostly explicit and associative, thoughthere have been claims for one case of implicit learning (see Segerdhal et al. ).But, in all cases, the lexicon peaked at around – words after years of learning

37 The scare quotes are due to the fact that the syntax of these so-called languages is generally extremelyimpoverished (for an excellent discussion, see Anderson ). However, this impoverished syntax hasnothing to do with their lexicons.


(as a means of comparison, this is about the same size as the lexicon of a -year-oldchild). As Bloom (: –) notes, this tells us that word learning in humans ispresumably not purely associative, as ‘nonhuman primates, who are excellent atassociative learning and have rich perceptual and motor systems, are quite abysmal atword learning’. More importantly for the present purposes, it may tell us a lot aboutthe conceptual abilities of non-human animals. Additionally, the (correct) fact thatnon-human primates have ‘rich perceptual and motor systems’ does not mean thatthese function in exactly the same way as do the corresponding perceptual systems inhumans (see Section ...).

Let me elaborate on the link that Bloom’s criticism of associationist accounts oflexical learning suggests between perceptual abilities and word learning, because thesame link surfaces for conceptualization. Bloom’s target here is an account accordingto which words become associated with their referents through repeated observedcorrelations between the word and the referent.38 According to the theories thatBloom is criticizing, the child hears the word and sees the object and associates theword with the object. Clearly, however, there is something missing to the story. Giventhat, even if we restrict ourselves to nouns (verbs and adjectives are obviously evenmore difficult to fit into this simplistic story), words do not refer to specific individ-uals but to objects belonging to the set of such objects as the one perceived, simpleperceptual abilities cannot do the trick. Abilities for categorization have to beinvolved. In other words, one can only learn a word if one is able to categorizeobjects as falling under the corresponding category. If this is the case—and it seemsto be a reasonable assumption—then the lexical acquisition ability of a given indi-vidual will depend on her ability to categorize. Thus, the extent of the vocabulary ofan individual is at least a rough guide to her categorization ability.39

So the very fact that non-human apes engaged in animal language programmeshave reached a ceiling at – words, while humans go to , words andbeyond (and -year-olds have lexicons of around , words), is a good indicationthat the conceptual abilities of apes and humans are dramatically different. Whyshould this be so? There is no clear answer (though, for a tentative explanation, seeSection ...), and the literature on animal conceptual abilities is fraught withdifficulties owing both to terminological confusion and to fundamental disagree-ments. Indeed, quite a few researchers claim that not only apes but monkeys are asgood at categorization as humans (see, e.g., Fabre-Thorpe et al. ). This makes therather poor performances at lexical acquisition of apes engaged in animal languageprogrammes even more puzzling. Additionally, the learning processes through which

38 Note that the criticism proposed against Millikan’s account in Section .. also applies here. I willhave more to say about lexical acquisition in Chapter .

39 It is only a fair and not an absolute guide because, as already mentioned (see Section ...), someconcepts may not be lexicalized and individuals may thus have larger conceptual apparatuses than lexicons.


both the lexicon and the categories are acquired in animals and in humans seem verydifferent, as we shall now see.Let us begin with animals (apes) engaged in animal language programmes. They

were taught either a simplified version of sign language40 or an artificial ‘language’made of visual symbols of a more or less abstract kind (so-called lexigrams—seeSegerdhal et al. ). In all cases (but for one, which will be discussed later),words are taught through repeated presentation of the word (in isolation) and acorresponding object, with the apes being encouraged to reproduce the word or givethe appropriate object and being given food rewards when they succeeded in doingso. Obviously, this is very different from the way children acquire the lexicon.Even if we set aside the not uninteresting fact that children usually are not

presented with words in isolation, children do not need a great number of trials tolearn a new word. In fact, the experimental literature shows that more often than nota single trial is enough, even if the object is unfamiliar (see Bloom ). And, moreanecdotally, children do not need any incentive (such as a food reward). But, mymain point is that, regardless of incentives and of whether the word is presented inisolation or in an utterance, children do not need numerous trials to acquire newwords, while apes do. The single case that might seem contradictory is the case ofKanzi (for a description, see Segerdhal et al. ). Kanzi is a bonobo who was raisedin the Language Research Center (LRC) in Atlanta. Being an orphan, he was adoptedby a foster mother, Matata. Kanzi, being deemed too young, was not engaged inlanguage training, but Matata was, and Kanzi was present during her (unsuccessful)training. When Matata was removed for breeding purposes, the researchers at theLRC discovered that Kanzi, simply by being present at Matata’s side when she wasundergoing training, had actually learned some of the lexigrams that she had failed tomaster. Kanzi then went on to an implicit (rather than, as hitherto, explicit) languagetraining, in which he participated in activities with his trainers, who would commu-nicate with him through English, while he communicated through the lexigram-keyboard. This, or so it has been claimed (see Segerdhal et al. ), means that Kanzihas acquired language just as young children do.I am not interested here in the claim that he acquired language. Rather I am

interested in the claim that his lexical acquisition was similar to that of children.A first important thing to note is that, although Kanzi was not himself engaged inlanguage training in the systematic and associative way described above, Matata was,and he was exposed to that repetitive training through being with her at the time. Itwould clearly not be correct to describe that procedure as on a par with what occursin human lexical acquisition. When, on discovering that he had mastered some

40 The version of sign language they were taught had few function words (usually prepositions) and noflexional morphology, which is why Anderson () rightly remarks that they were not taught anythingreally like a natural language.


lexigrams, his new training was put into place, he was exposed to people talking tohim, but it is not clear how often the same words, coupled with the same objects, wererepeated. So, on all counts, Kanzi does not seem to be an objection to the claim thatchildren need much less exposure to repeated couplings between words and objectsthan do apes.

So, to sum up, not only are apes’ vocabularies highly limited relative to humanvocabularies, but the very process of acquisition of the words in these vocabulariesseems a much more protracted affair in apes than it is in children. On the view thatlexicon size is a good (if rough) indicator of the richness of conceptual apparatus, theconclusion is that non-human primates’ conceptual apparatuses are incommensur-ably poorer than are those of humans. And, in view of the difference between thehuman and non-human abilities to learn words, one may think that this is basicallydue to differences, not in memory or whatever other cognitive ability, but in theirability to conceptualize and categorize objects.

.... A potential objection

One potential objection to that argument comes, not from apes engaged in animallanguage programmes, but from two studies on dogs. The first one (see Kaminskiet al. ) used a Border Collie, named Rico, who was a family dog, and had beentrained, as a game, to retrieve objects. The experimental testing showed that,throughout his life (Rico was years old at the period of testing), Rico had indeedmastered more than words. However, there were limits to the study. For onething, Rico seems to have mastered, if anything, proper names rather than commonnouns. If this is the case, no categorization or conceptualization needs to have beeninvolved. Arguably, his knowledge could be based on simple association betweenacoustic sequences and specific objects. Apart from the fact that his vocabulary isslightly smaller than is that of animals engaged in animal language programmes,having mastered only proper names, his achievement is not relevant to an investi-gation into animal categorization abilities.

Sensitive to those objections, Pilley and Reid () trained a female Border Colliepuppy, Chaser, for three years (from the time she was months old) on lexicallearning. A first experiment centring on proper names (again no categorizationinvolved) showed her to be able to master , names for different specific objects,all of them toys of one sort or another. Additionally, the training was stopped afterthree years, when that number was reached, so it is entirely possible that, givenfurther training, Chaser might have gone well over that limit. In another experiment,still involving Chaser, Pilley and Reid were able to show that she was able to learnnames for categories (balls, Frisbees, and toys), using the same , objects that wereused in her proper name training. What is more, one of these categories, toys, wassuperordinate relative to the other two—that is, balls and Frisbees.


So what could we conclude from Chaser’s exploits? A first conclusion drawn fromthe first experiment seems to be that it is unlikely that the vocabulary limits evidencedby apes engaged in animal language programmes are due to memory constraints.Chaser was able to master , words in three years and had not reached her limitswhen the experiment stopped. That is a lot more than the –words that apes areable to master after a much longer period of training. This conclusion is reinforced byFagot and Cook’s comparison () of long-term memory capacities in pigeons andbaboons. While pigeons could memorize no more than –, picture-response(arbitrary) associations, baboons could master between , and , items andwere still learning new itemswhen the study was discontinued (hence, just like Chaser,they had not reached their peak). This indicates that, indeed, animals, and notablyprimates, have important capacities for long-term memory storage.What about the latter experiment in which Chaser had to learn three common

nouns (implying categorization)? The first thing to note is that she had to learn onlythree common nouns–categories association (rather a measly number compared tothe – words in ape vocabulary41). However, there are more than a few pointsof interest. The first is that the three categories, toys, balls, and Frisbees, correspondedto the objects with which Chaser had been familiarized in the first experiment.42

Pilley and Reid see the fact that Chaser had already acquired proper names for eachof these objects as an additional difficulty. Their idea is obviously that the existence ofwords for each of these objects (the proper names) might interfere with the learningof names for the three categories under which these objects were put. Be that as itmay, regarding categorization, it is not clear that familiarity with the objects mightnot ease the process. Let me now separate the two ‘basic’ categories (balls andFrisbees) from the ‘superordinate’ category (toys).All three categories were taught in a similar manner: Chaser was trained to

associate the new word (either ‘ball’, ‘Frisbee’, or ‘toy’) with the objects belongingto the corresponding category. The training proceeded as follows: the dog waspresented with sixteen objects, half of which corresponded to the category and halfof which did not. For the two basic categories, balls and Frisbees, all sixteen objectswere objects with which she was familiar from the first experiment. For the super-ordinate category, toys, the eight objects corresponding to the category were objectswith which she was familiar from the first experiment, while the eight objects that didnot belong to the category, though familiar in themselves (they were ordinaryhousehold objects, such as shoes, socks, and so on43), had not been used in the firstexperiment. Chaser was encouraged to bring objects that corresponded to the word

41 Though, in all fairness, those – words presumably counted a few proper names.42 Nonewobjectswere introduced, and indeedall the tests in this latter experimentwere conductedon the,

objects for which Chaser had acquired proper names, as this latter experiment was conducted after the first one.43 And Chaser was also a family dog, in addition to being an experimental subject.


used and was subjected to numerous trials. Importantly, as we shall now see, thetesting was done for a single category at a time.

During testing, Chaser underwent separate testing for each of the categories shehad been trained on—that is, one test session for ‘balls’, one for ‘Frisbees’, and one for‘toys’. She was presented with an array of sixteen objects, half of which belonged tothe category being tested and half of which did not. These objects were not those onwhich she had been trained, though for the two basic categories, balls and Frisbees,they were objects that she was familiar with from the first experiment. For thesuperordinate category, toys, again, none of the test objects was an object withwhich she had been trained, but the eight objects falling under the category wereobjects used in the first experiment. Chaser was told to bring one object belonging tothe category, eight times in a row (and the objects she took were not replaced).

So what conclusion can we draw from this second experiment? First of all, let mepoint out that, if Pilley and Reid had succeeded in showing that Chaser was able toacquire a superordinate concept, this would be a major result, as there is seriousdoubt as to whether animals have the kind of conceptual hierarchies (for example,ANIMAL—MAMMAL—CANINE—DOG—CHOW) that are typical of maturehuman conceptual apparatuses (see Section ... for further discussion). Whetherthey have succeeded in doing so is, however, doubtful. Having mastered a super-ordinate concept entails being able to conceptualize the corresponding category assubsuming several other categories. But it is not clear that this can be evidenced bytesting each category in isolation, as Pilley and Reid did. An additional test involvingthe three categories simultaneously would have been necessary, where Chaser couldhave been ordered to bring back the ‘toy/ball/frisbee’. Obviously, this would haveentailed a bigger and more mixed collection of objects, but the absence of such a testleaves it an open question whether Chaser has indeed mastered the superordinatecategory toys as superordinate. There is an additional worry with the category toys.As already mentioned, while Chaser was trained (and tested) for both balls andfrisbees with objects with which she was familiar (and indeed had proper names for)from the first experiment, this was not the case for the category toys. There, she wastested both with familiar objects from the first experiment (all TOYS) and withunfamiliar objects (all NON-TOYS). The same was true in the testing. What is more,on Pilley and Reid’s own admission, Chaser, being a family dog, was forbidden toplay with anything in the house that was not one of her (,) toys—that is, she wasforbidden to play with socks, shoes, and so on. All these forbidden objects wereNON-TOYS (Pilley and Reid indicate that this was their own criterion to sort toysfrom non-toys). Both the familiarity of the ‘toys’ and the non-familiarity of the ‘non-toys’ and the fact that ‘non-toys’ were forbidden objects seem to be confoundingfactors regarding the category toys. Here, one could argue that all Chaser had to dowas to learn a word, rather than acquire a category (which she presumably alreadyhad as ALLOWED versus FORBIDDEN).


To sum up, it is unlikely that Chaser actually learned a superordinate concept. Butthere is no reason to doubt that she has mastered two common nouns correspondingto two categories. Though nice, this is hardly an earth-shattering result (not manydog owners would be surprised by it). The main interest of Pilley and Reid’s studythus lies in the first experiment, which makes any explanation of the limitation of apevocabularies in terms of limits in the capacity of long-term memory storage stronglyimplausible.

.... The limitations of animal conceptualization

As we have seen, and Pilley and Reid’s study () hardly contradicts this, it seemsthat animals need repeated trials to learn new words, while children learn themmuchmore readily and indeed often learn them on the basis of a single exposure. Taken intandem with the enormous discrepancy between ape vocabularies and humanvocabularies, this suggests that one explanation for the limitation of ape vocabulariesmay be that they are much less good than children at learning words. So it is worthlooking at what is involved in learning a new word. As already argued (seeSection ...), a word44 refers to a category, not to a specific single object. If so,there are two possibilities:

• learning a word is associating (in the vernacular, not in the technical, sense) itwith a pre-existing category;

• learning a word is associating it with a new category.

In the first case, the task is mainly one of matching the word and the pre-existingcategory. In the second case, the matching can occur only when the relevantconceptualization has been made. What I want to suggest is that it is the conceptu-alization process that may be different between humans and non-human animals,notably but not only primates. Before defending this view in detail, however, I wantto pre-empt a (potential) objection.It has been (rightly) claimed (see, e.g., Hirsh-Pasek and Golinkoff ; Bloom

) that children’s lexical acquisition makes use of social cognition to identify thereference of a new word. Apes, being less socially adept than children, would not beable to do so, which would impede their word learning. This objection is withoutmerit, because of the very different situations in which children and apes (Kanzinotwithstanding) acquire language. Children basically use their social abilitiesbecause of the fact that the words they acquire do not usually occur in isolationand neither are they always presented simultaneously with a single salient object towhich their attention is directed. Rather the words occur in utterances that may not

44 Barring proper names, which are a relatively minor proportion of human vocabularies anyway andwhich were not counted in the estimates for human vocabularies given above.


even be addressed to them and the putative referents are not explicitly singled out.Hence, children have to infer the speaker’s referential intentions, which is where theirsocial skills come in. But, this is not a problem that apes have to solve when learning anew word. They are repeatedly presented with the word and with the single object(representing the category) it refers to. So the objection is worthless. It is important tonote, additionally, that, once the child has identified the referent, if she does notalready have the corresponding concept, she still has to do the conceptualizationbefore the link between the word and the category can be established. There, hersocial skills will not be helpful.

So let us go back to specificities of human conceptualization relative to non-humanconceptualization. One hotly debated topic is whether conceptual hierarchies arespecific to humans (see the discussion about TOY in Section ...) or whether theyare widely shared among animal species. Conceptual hierarchies are due to thecategorization of one and the same object at different levels of abstraction: forinstance, my dog Izuki is a CHOW, a DOG, a MAMMAL, an ANIMAL. The featuresshared by all individuals belonging to a lower category (for example, chows) are morenumerous than those shared by all individuals belonging to a higher category (forexample, dogs) and so on, climbing up the hierarchy. This means that, the higher onegets into the hierarchy, the more abstract are the corresponding concepts. The factthat lower nodes inherit features from higher nodes means that conceptual hierarch-ies are inference pumps. In other words, one characteristic of conceptual hierarchies(which can be represented as upside-down trees) is that the lower nodes inherit allthe features from the higher nodes, but not vice versa. One intriguing question iswhether there is a privileged level at which an object is conceptualized—that is, whereit will be conceptualized faster, more often, and which will, in humans, correspond toa more frequent word that those used for the other levels. Rosch et al. (: )have examined several hierarchies, both natural and artefactual, in humans andconcluded that such a privileged level—called the basic level—is determined by thefollowing properties: ‘Basic objects are the most inclusive categories whose members:(a) possess significant numbers of attributes in common, (b) have motor programswhich are similar to one another, (c) have similar shapes, and (d) can be identifiedfrom averaged shapes of members of the class’. Thus, the basic level is largely due tothe perceptual properties of the categories. It turns out that species (for example,DOG, CAT) are usually the basic level for mammals, but BIRD is the basic level forbirds as is FISH for fishes. Thus, the basic level does not correspond to a biologicallevel (while DOG and CAT correspond to species, neither BIRD nor FISH does). Thedetermination of the basic level according to the principles indicated here is a resultof the categorization process in humans, which is why it is of central interest to us.More generally, the importance of conceptual hierarchies, beyond their potentialimpact on human cognition via the inferences that they allow, is due to the fact thatthey seem to be a central and universal feature of human conceptualization (see, e.g.,


Berlin ; Malt ; Atran and Medin ).45 Thus, it is interesting to seewhether and how readily other animal species, and notably other primate species,can form conceptual hierarchies.The first study of categorization46 by non-human animals at several levels of

abstraction was done by Roberts and Mazmanian (). They used six pigeons,four squirrel monkeys, and thirty humans as subjects. The task was a forced dis-crimination task at three levels of abstraction: KINGFISHER versus BIRD, BIRDversus OTHER ANIMAL, ANIMAL versus NON-ANIMAL. The subjects werepresented with two images, one corresponding to the category being learned andone that did not, and they had to choose the right one. Animals were presented withnumerous trials during training for each category to be learned and correct choiceswere rewarded. Roberts and Mazmanian examined the acquisition curves for all threegroups, as well as accuracy in subsequent testing with new items. There were strikingdifferences between the learning curves of the three groups. Pigeons learnt the mostconcrete category (kingfishers) much faster than they did the most abstract category(animals) and never mastered the intermediate category (birds). Monkeys learnt themost concrete (kingfishers) and most abstract (animals) categories at the same rate,but were slower in their acquisition of the intermediate category (bird). Humanslearnt all three categories much more quickly than did both animal groups, but foundthe intermediate (bird) and abstract (animal) categories easier to learn than the mostconcrete category (kingfisher). Regarding accuracy, the results were similar forpigeons and monkeys, which were significantly above chance for the most concretecategory (kingfisher), but were at chance for the intermediate (bird) and abstract(animal) categories. Human subjects were at ceiling for all three categories. Furtherexperiments provided more training to pigeons and monkeys on the intermediate(bird) and abstract (animal) categories, leading to better accuracy for the abstractcategory, but not for the intermediate one. The overall conclusion that can be drawnfrom Roberts and Mazmanian’s study () is that conceptual hierarchies, whichrest on the ability to categorize the same items at several different levels of abstractionand which are easily accessible to humans, are less accessible to other species,including primate species. Additionally, in this study, the intermediate categorywas clearly basic in the sense of Rosch et al. (), and was easily accessed byhumans, but was inaccessible to the two non-human groups. This suggests thatprocesses of categorization may be different in humans and non-human animals, a

45 Note that this does not mean that one can have the concept DOG iff one also has the conceptsCANID, MAMMAL, or ANIMAL. Presumably, very young children have the concept DOG before theyhave the other superordinate concepts. The importance of conceptual hierarchies lies rather in what theyreveal about the human ability to acquire concepts.

46 Roberts and Mazmanian’s paper uses the terminology of ‘concept learning’. It is not clear that it isappropriate, however, and I will rather use ‘categorization’ here.


conclusion that is reinforced by the number of trials that were necessary for animalsto learn the two categories they mastered relative to humans.

This raises two questions. In humans, categorization is spontaneous (hence the quickacquisition curve of humans inRoberts andMazmanian’s study): howwouldnon-humanprimates do on a spontaneous categorization task? The second question has to do withthe phylogenetic differences between humans and pigeons (obviously huge), but alsobetweenhumans and squirrelmonkeys:47 so howwould the other species of apes performrelative to conceptual hierarchies? There have been relatively few studies on categoriza-tion in apes, but there are some in common chimpanzees, gorillas, and orangutans.

Fujita and Matsuzawa () produced a first study, using a single chimpanzee,with a single category, humans. The subject was Ai, a -year-old female who had along history of (artificial) language training. The task was very simple: the chimpan-zee was presented with a single image on the screen. She had to press a button andwhen she stopped doing so, a new image was presented after a short interval. In otherwords, the presentation of images was self-paced and the measure was the durationduring which the chimpanzee pressed the button to retain the image on the screen.There were five sets of images: ‘humans’, ‘no humans’, ‘ambiguous’ (very small andhard to read images with humans), ‘light’ (a blank light screen) and ‘no light’ (a blankblack screen). Ai saw each image several times, and completed , trials. Her orderof preferences was ‘humans’, ‘ambiguous’, ‘no human’, ‘light’, ‘no light’. The differ-ence between duration time for ‘humans’ and ‘no humans’ was significant. In otherwords, Ai was able to identify humans in a variety of pictures, despite the variationsin size, number, clothes, angles of vision, and so on.48

Brown and Boysen () produced the only other study on spontaneous dis-crimination (rather than categorization) in chimpanzees (Pan troglodytes). Theirsubjects were six chimpanzees (four males and two females, aged from to ).They used a same/different paradigm (over which the animals had been trainedbeforehand) and tested the categories chimpanzees, gorillas, domestic cats, tigers,and fish. The chimpanzees were presented with pairs of images that could bothbelong to the same category, or belong to different categories. They were given achoice of two symbols, one for same and one for different (with which they werealready familiar). All categories were used in any session, as the judgement was same/different rather than, for example, chimpanzee/not chimpanzee (hence it was a taskof discrimination rather than categorization49). The animals were tested directly,without any training. Results indicated that chimpanzees were above chance for all

47 Squirrel monkeys being New World primates, the last common ancestor between them and thehominid lineage goes back to about forty-five million years ago (see Takahata and Satta ).

48 Fujita and Matsuzawa () note that, given her extensive frequentation of humans, pictures ofhumans were reinforcing for Ai.

49 All of the categories (apart from fish) were chosen for their perceptual similarity (i.e., chimpanzeesand gorillas; cats and tigers).


five categories. A major question is whether all of these are basic categories in humanterms. While there is no doubt that fish, cat, and tiger are, one may be more doubtfulabout chimpanzees or gorillas, whom non-expert humans may tend to dump in awider monkey category, along with macaques and baboons (that is, they seem to besubordinate, rather than basic level categories). Still, the results seem to indicate thatchimpanzees are well able to discriminate spontaneously at least some basic levelcategories (including some with which they were not familiar, such as fish, tigers, andgorillas). Brown and Boysen (: ) rightly conclude:

‘If basic-level categories are determined largely by the structure of the stimuli (Malt, ),then it is not surprising that humans and chimpanzees would share many such categories,because it is likely that the perceptual mechanisms that subserve visual processing are quitesimilar, reflecting the two species’ relatively recent evolutionary divergence’.

Yet the limits of the study, in addition to the fact that it targets discrimination ratherthan categorization, is that it tests only basic (and maybe subordinate in the case ofchimpanzees and gorillas) level categories.Let us now turn to two studies that revert to Roberts and Mazmanian’s method-

ology () and target respectively gorillas and orangutans. Vonk and MacDonald() tested a -year-old female gorilla (who had been raised by humans) on severalcategories at the concrete, intermediate, and abstract levels. The acquisition curveswere different depending both on the category tested and on the complementarycategory, as shown in Table ..The gorilla showed transfer (criterion: per cent or more success on new images)

for all concrete categories as well as for the two abstract categories. The intermediatecategory was clearly more difficult for her, as twenty-three sessions were needed andthe animal never quite reached the criterion (peaking at per cent of successfulidentification). So it seems that, as in Roberts and Mazmanian’s study (), theintermediate category was the most problematic one. However, one may wonderwhether it was the intermediate or the concrete categories that should be regarded as

TABLE .. Gorilla’s acquisition curve

Type of category Category Number of sessions

Concrete Gorillas versus humans Orangutans versus humans Orangutans versus other primates Gorillas versus other primates

Intermediate Primates versus non-primates Abstract Animals versus non-animals

Food versus animals


basic.50 While the animals and food categories would no doubt count as superordin-ate for humans, it is not clear whether the gorillas and orangutans categories shouldbe considered as basic, or whether it is the primates category that should be soconsidered. Though there are no studies in humans on the categorization of primateseither at the level of the individual species (for example, gorillas, orangutans), or atthe intermediate level (primates), it seems likely that, outside of experts, humansubjects would have primates (linguistically designated as ‘monkeys’) as the basiclevel. If this is right, then, as in Roberts and Mazmanian’s study, the most difficultlevel for the gorilla was the easiest for humans—that is, the basic level, suggesting thatdifferent categorization processes are used in the two species.

Be that as it may, let us now turn to Vonk and MacDonald’s study () withorangutans. The subjects were six captive orangutans (three males and threefemales), aged from . to . The acquisition curves are indicated in Table ..

As noted by Vonk and MacDonald (: ), there were ‘significant individualdifferences, and therefore it is difficult to make general conclusions’. The importantvariations regarding acquisition curves (see Table .) are also reflected by the factthat, during transfer to new images, some subjects failed to reach the criterion ( percent successful choices) for some categories. Nevertheless, all categories were mas-tered by some of the subjects. So a tentative conclusion is that orangutans, in contrastwith monkeys and gorillas, are able to grasp intermediate categories and, thus, toaccess categories that are basic for humans.

So, to sum up, setting chimpanzees aside, on the face of it and with the potentialexception of orangutans, it appears that animals are generally poorer than humans atconstructing conceptual hierarchies (that is, at categorizing the same objects atdifferent levels of abstraction) and may in fact have specific difficulties with theeasiest level for humans—that is, the basic level. Given the definition of basic level

TABLE .. Orangutans’ acquisition curve

Type of category Category Number of sessions

Concrete Orangutans versus humans –Orangutans versus other primates –Orangutans versus red other primates –

Intermediate Primates versus non-primates –Abstract Animals versus non-animals –

Food versus animals –

Note: The number of sessions gives the range of sessions needed by the different subjects (the first corresponds tothe fastest subject, and the second to the slowest subject).

50 The question did not arise for Roberts and Mazmanian’s study, as the intermediate category therewas birds, which would undubitably be basic level for humans (though maybe not for ornithologists).


categories given by Rosch et al. (), which seems to be fundamentally dependenton perceptual and notably visual features, this suggests that visual perception mightfunction differently in humans and in non-human primates.However, a spate of work on rapid visual categorization has come to shed doubt on

this view. In , Thorpe et al. showed that natural photographs presented for a veryshort period of time (ms51) will be very quickly categorized at a superordinate level(for example, animals) by both monkeys and humans. The behavioural response isgiven in – ms by humans and ms in monkeys.52 By contrast, basic levelcategorization (for example, dogs) under such conditions is difficult for humans (ithas not been tested in monkeys). Given that at such speed the visual treatment canonly be limited and feed forward rather than feed back (in other words, bottom uprather than top down), this suggests that basic level categorization cannot be theeasiest level of categorization, even for humans. In other words, it needs a moreelaborate visual treatment than this speed of presentation-response can allow. And,in fact, it has been found that, to access the basic category, humans need anadditional – ms of processing time (see Macé et al. ; Fabre-Thorpe ;Praß et al. ). This also suggests that superordinate categories are not the result ofa process of pruning down the elaborate representation that would support a basiclevel categorization to ‘abstract away’ from it, but rather that they are directly accessed,and have to be enriched53 for the basic level of categorization to be achieved.Fabre-Thorpe () suggests that the faster reaction time for basic level categor-

ization found in humans could be an artefact of the methods used, as most tasks haveasked subjects to name the category. Given that basic level category nouns have muchhigher frequency than do subordinate or superordinate level categories nouns andgiven that lexical frequency affects linguistic retrieval, the speedier responses for basiclevel categories could be explained by the fact that the nouns corresponding to themare more easily retrieved than those corresponding to the subordinate and super-ordinate levels.While this may be true, it still leaves unexplained why, if they are more difficult to

access, basic concepts should indeed correspond to more frequent words. This veryfact suggests that the corresponding categories are of specific interest to humans, andmay be more salient to them, if they are given the time necessary to process deeplyenough the visual scenes in which they appear. And, if this is the case, the categor-ization story may in fact be rather more complicated than was previously thought.I will come back to this later, but I would first like to comment more generally on the

51 Milliseconds.52 Most probably, one should not make too much of the faster response of monkeys over humans:

Fabre-Thorpe () notes that it is presumably due to the fact that the monkey brain is much smaller thanthe human brain and the nervous impulse just has a shorter path to cover.

53 Note that this does not necessarily suppose a two-steps procedure. The enrichment necessary toaccess the basic category may just be the result of the visual treatment of the scene, given more time.


superordinate categories that have been used in all these experiments—that is, boththe animal experiments just described and the rapid visual categorization tasks.

As the two chimpanzee studies did not use superordinate categories, this leaves uswith the squirrel monkey, gorilla, and orangutan studies. In the squirrel monkeystudies, Roberts and Mazmanian () used animals as a superordinate category. Inthe gorilla study, Vonk and MacDonald () used animals and food and they usedthe same superordinate categories in the orangutan study (see Vonk and MacDonald). In the rapid visual categorization studies, in a study with rhesus monkeys,Fabre-Thorpe et al. () used animals and food again. Other studies with humanshave added (occasionally) a third superordinate category, vehicles.

Let me begin with the animals superordinate category. Arguably, animals is arather special category, because, as proposed by New et al. (), it has evolutionarysignificance. New et al. tested a specific categorical attention for animals in humans,using a change detection paradigm. A robust result in the experimental literature onvision is that people often fail to detect sizeable changes when they occur during asaccade or when the subject’s attention is otherwise engaged. This phenomenon isknown as change blindness (see Rensink et al. for the princeps study, andChabris and Simon for a general overview). Hence, a change detection para-digm is a good way to assess heterogeneous attention—that is, cases where a givenelement in the visual field will grab the viewer’s attention independently of hervolition. Thus, if it is easier to detect a change in an element of the visual fieldbelonging to a given category than it is to detect a change in another element of thevisual field belonging to another category, one can conclude that elements belongingto the first category are attention-grabbing for one reason or the other. In a series ofexperiments, New et al. () were able to show that humans were much better, interms of both accuracy and response time at detecting changes in animate rather thanin inanimate elements in a visual scene. This was even true when the inanimateobjects were vehicles, showing that motion was not the crucial element in the animateadvantage. This suggests the evolutionary importance not only of detecting membersof animate categories but also in carefully monitoring them (which explains why theyare attention-grabbing). This is understandable, considering that animate things canbe predators, and, even though the attention-grabbing potential of animate thingshas not been tested in non-human animals, it makes sense to suppose that all animalspecies54 are sensitive to the presence of animate things in a visual scene. This mightexplain why all the primates in the categorization experiments already describedseemed able to master the superordinate category animals, and why both humans

54 With the potential exception of birds, who, being flying animals, are not subject to quite the sameamount of predation from terrestrial animals. On the other hand, birds seem especially good at detectingmotion, which, again, makes evolutionary sense.


and monkeys in the rapid visual categorization studies were also able to detectanimals very quickly after a short presentation of a visual scene.What about the other superordinate categories: food and vehicles? Regarding food,

though it certainly does not warrant the careful monitoring that animals do, it iscertainly an evolutionary relevant category, likely to be attention-grabbing in its ownright. Thus, it is hardly surprising that the primates in all the studies mentioned so farwere able to detect food in a visual scene. Indeed, it is interesting that, in the rapidvisual categorization study with monkeys (see Fabre-Thorpe et al. ), monkeyswere slightly less accurate with animals ( per cent correct) than with food(. per cent correct), but were faster at detecting animals ( ms) than food( ms). This makes sense from an evolutionary point of view, as false positives areless dangerous than false negatives relative to predation, while speed is of the essence.Regarding the last superordinate category, vehicles, which was tested only with

humans, it is hardly surprising that humans did as well on that category as they didon the animals category, because humans in industrial societies are ‘experts’ onvehicles, as Fabre-Thorpe () herself recognizes, and expertise has been shownto speed up categorization.So, a reasonable conclusion may be that, in the rapid visual categorization studies,

both monkeys and humans did not truly ‘categorize’ but rather merely detected thepresence of animals and food. Humans did categorize vehicles, based on theirsuperior expertise. Regarding the animal study, the same explanation may apply tosuperordinate categories (animals and food), and, as we saw, the intermediatecategory was rather difficult, though orangutans had a modest success with it.So, do animals actually manifest the ability of building conceptual hierarchies?Chimpanzees seem able to entertain basic level categories as well as subordinatecategories (chimpanzees, gorillas) as do both gorillas and orangutans. It is doubtfulthat gorillas can access basic level categories, while the evidence is less clear-cut fororangutans. So none of the studies described above shows that non-human pri-mates have access to the rich conceptual hierarchies that are the hallmark ofhuman conceptualization.

.... The roots of conceptual hierarchies

The question that immediately arises is why humans should have this much moreproductive ability to categorize. There does not seem to be much doubt that theexplanation for the richness of the human conceptual apparatus is largely due to thepossibility of placing the same object in different categories. This argues for an abilityfor abstraction that may be lacking, partly or completely, in non-human primates. Sowhere does this ability come from? Here, an important question is whether thestudies described actually show evidence of categorization or whether they merely


show evidence of discrimination. Clearly, Brown and Boysen () show evidencefor discrimination rather than categorization. However, one might argue that this isactually the case for all the animal studies described above.

Let me begin by indicating the way in which discrimination and categorization aredifferent. A good example here is the case of colours. Humans with typical visualperception, presented with two slightly different swatches of blue, will usually be ableto discriminate between them. This does not mean that they have correspondingconcepts—for example, BLUE and BLUE. Rather it means that we can discriminatebetween things without necessarily having concepts for those things between whichwe can discriminate. This is because discrimination is necessary to allow us tocategorize objects that fall under a different concept, but not sufficient to show theexistence of a category (whose existence depends on that of the correspondingconcept). So categorization is dependent on discrimination (one cannot categorizethings without discriminating between them), but not the reverse. Hence, ourcapacities for discrimination (and presumably those of non-human animals aswell) far exceed our capacities for categorization. To categorize rather than merelydiscriminate, we need to have (or to acquire) the corresponding concept. This iswhere Fodor’s criterion for possessing a concept—that is, being able to use theconcept in thought—is clearly superior to Millikan’s—that is, being able to identifythe objects falling under the corresponding category. Millikan’s criterion does notallow a clear distinction between mere discrimination and true categorization(depending on concept possession), while Fodor’s does. What the animal studiesdescribed (including Fabre-Thorpe et al.’s study () with rhesus monkeys in arapid visual categorization task) establish is the ability to identify objects as fallinginto classes (to discriminate), but they tell us nothing about whether the subjectspossess or acquire the corresponding concept.

So what could show that animals have the corresponding concept—that is, whatcould show that they are categorizing and not merely discriminating? And whyshould we consider that the humans engaged in rapid visual categorization studiesactually have the concepts for animals, food, or vehicles, while we deny that thesestudies show this to be the case for the monkeys? After all, as Fabre-Thorpe (,) notes, humans and monkeys have equivalent performances in these tasks. Soare we not adopting an inacceptable double standard? As a matter of fact, we are not.From the rapid visual categorization results, the only thing we can conclude is thatboth humans and monkeys discriminate. But we are not entitled to conclude thateither species categorize in these tasks. So why should we conclude that humans havethe corresponding categories and reserve our judgement regarding monkeys? Inhumans, we have additional evidence of concept possession for the superordinatecategories tested. This additional evidence comes from language. Humans can talkabout animals, food, vehicles, and many other things, giving evidence that they can


think about them.55 This, basically, corresponds to Fodor’s criterion for conceptpossession. (Note, however, that, while humans do have these concepts, this does notmean that they use them—that is, that they do categorization rather than merediscrimination—in the rapid visual categorization task.)It is important to note that, while the studies presented do not allow us to conclude

that the subjects categorize, they do not allow us either to conclude that they didnot categorize—that is, they do not allow us to conclude that the subjects do nothave or acquire the corresponding concepts.56 Rather, they leave the question open.For the sake of argument, let us suppose that, in these tasks, subjects, whether humanor non-human, actually categorize—that is, that they have (or have acquired) thecorresponding concepts and use them in the task. What does this tell us aboutthe nature of concepts in humans and animals? Are they similar or different? Or, toput it another way, do they allow the same sort of thoughts in humans and non-human animals?Returning to the animal experiments described in this chapter, the ‘superordinate

categories’ that apes and monkeys seem able to ‘master’ correspond to what Gibson() called affordances in his theory of ecological perception.57 His view was thatan organism perceives the world by directly identifying the opportunities for action(or affordances) that its immediate environment provides. Affordances can be posi-tive (for example, food) or negative (for example, at least potentially, animate things)and they can trigger action, including vigilance. Affordances seem to be of such anature that at least some of them will be perceived very quickly (just as animals andfood were in the rapid visual categorization tasks described). They also clearlycorrespond to what Millikan calls pushmi–pullyu representations (see the discussionin Section ..)—that is, representations that at once indicate and instruct. Whileaffordances have some affinities with categories (that is, they delimitate non-arbitraryclasses of objects), it is not clear that they can be seen as concepts in the sensediscussed, rather than as proto-concepts. Being indicative, they have something incommon with concepts, but being instructive, they lack the strong decoupling that ischaracteristic of human concepts and thought. Let me elaborate.Decoupling in language corresponds to the possibility of referring to an object (or

a category) in the absence of the object in question from the environment (seeChapter and Section ..). If we transpose the notion to thought, we can

55 Note that basically the same reasoning goes for animals engaged in animal language programmes.However different their ‘words’ are from words in human lexicons, the very fact that they can use them inutterances (however these may differ from the utterances in natural languages) is a strong cue to the factthat they possess the corresponding concepts.

56 Indeed, as we saw, humans may have discriminated, rather than categorized in those tasks, but thisdoes not mean that they do not have the corresponding concepts.

57 As an example, regarding the subordinate category in Roberts and Mazmanian ()—i.e., king-fishers—it is not clear that either monkeys or humans did anything more than discriminate. So we will leaveit aside here.


distinguish two different ways of understanding the notion, a weak one and a strongone (see Reboul ):

• Decoupling weakly understood occurs when a representation is deployed in acognitive process in the absence of its target.

• Decoupling strongly understood occurs when a representation is weaklydecoupled and when, in addition, the cognitive process is not oriented towardsaction (that is, the representation is not entertained as a means to any physicalaction).

Though there may be a temptation to think that animals do not entertain evenweakly decoupled thoughts, this would clearly be false, given the evidence forplanning in apes (and corvids, see Marzluff and Angell ). However, this doesnot mean that animal thoughts can be strongly decoupled. Regarding this point, it isinteresting to note that animals engaged in animal language programmes spontan-eously use ‘language’ only to request things or actions from others (mostly theircaretakers). Thus, their spontaneous utterances may be weakly decoupled (as theyask for objects or events absent from their immediate environment), but they are notstrongly decoupled, as the utterances are always oriented towards future action. Bycontrast, humans are able to deploy thoughts that are strongly decoupled in the sensethat not only do they bear on absent targets, but also they are not oriented towardsaction (indeed, the place that fiction—or, on a more anthropological vein, myth—takes in human lives is a good indication of that). Millikan () has rightly insistedon the potentiality for strong disinterestedness in human thought: humans, and—asfar as we know—only humans, are able to entertain thoughts that do not bear ontheir immediate environment and that, equally, are not oriented towards any action.Hence, the human ability for speculative thought of a non-practical kind.

So it seems that we are faced with two different, though not necessarily discon-nected, questions. First, why are humans and chimpanzees, but presumably no otherape species (with the potential exceptions of orangutans), able to access basic levelcategories? And, second, why are humans the only species, as far as we know, able tothink strongly decoupled thoughts?

Let us begin with the first question. In the introduction of their gorilla study, Vonkand MacDonald () discuss the differences in visual processing between humansand non-human primates. These can be assessed by asking people (or animals) tochoose a similar figure in an array of hierarchical figures (for example, a G—globallevel—made of small Hs—local level; a G made of small Ms; an L made of small Ms)or to find the odd man out. Humans will preferentially choose the same (or different)object at the global level, though, given slightly more time, they will also be able tochoose the same (or different) object at the local level (see, e.g., Navon ). In otherwords, they will perceive the global shape before the details of the object. On theother hand, monkeys (baboons) show a preference for the local level and are indeed


unable to access the information at the global level (Fagot and Deruelle ; Fagotet al. ), while the evidence regarding chimpanzees (the only apes to have beentested) is mixed. Fagot and colleagues (Fagot and Tomonaga ; Fagot et al. )found basically the same result for chimpanzees as they did for baboons, whileHopkins and Washburn () found a local preference in chimpanzees, but alsoan ability to access the global level of visual treatment. Note that if, as seems likely, atthe local level, details are treated in preference to shape, the results presented inSection ... for both animals and humans make sense. Animals are better thanhumans at subordinate level discrimination because they have a (strong) preferencefor details over global shape in visual processing (and members of subordinatecategories—for example, Siamese cats, Persian cats—differ mainly on details, ratherthan global shape). On the other hand, shape is extremely relevant at the basic level(remember Rosch et al.’s characterization of basic level objects), and one wouldexpect that an animal species capable of basic level categorization would also becapable of global visual processing, which seems to be the case in chimpanzees.Finally, there is no clear evidence for superordinate categorization (beyond affor-dance identification) in non-human animals (see Section ...), and it might beargued that the superordinate level is indeed the result of abstraction. If this isthe case, it may well be that in the end only humans are capable of that level ofcategorization.Coming back to basic concepts, could one say that they correspond to affordances

in chimpanzees (the only animals who seem to be capable of categorization at thatlevel)? Setting aside the animal categorization studies described (which may showdiscrimination rather than categorization, as we saw), chimpanzees engaged inanimal language programmes demonstrate their ability to form basic level categoriesthrough their vocabularies, as most of their words refer to basic level categories.58

Most of these words, from what one is able to gather from the rather imprecisereports available (see Anderson for a critical review of the animal languageprogramme literature), refer to toys, kinds of food, activities, and so on. So it may besaid, in all fairness, that those basic level categories do indeed correspond to affor-dances and thus indicate the possession of proto-concepts (not strongly decoupled)rather than concepts (strongly decoupled). Nevertheless, given that chimpanzeesseem to be the only species of apes incontrovertibly able to form categories at thebasic level, one may wonder why they are thus endowed. If, as already argued,chimpanzees’ basic concepts correspond to affordances, this can hardly be becauseother apes are limited to affordances: arguably, so are chimpanzees. But chimpanzeesseem to be able to form categories for affordances at different levels, while this is notthe case for other animals, including other apes.

58 Which is hardly surprising, given that they are taught their ‘languages’ by humans who just choosewhat is, for them, basic level vocabulary—i.e., vocabulary corresponding to basic level categories.


A tentative explanation may lie in the fact that chimpanzees in the wild are tool-using animals (see Section .) and use different tools in different situations and fordifferent purposes. This suggests that they need to be capable of finer-grainedcategorization that do other non-tool-using animals. It is interesting to note in thisregard that gorillas not only do not use tools in the wild, but seem unable to use themin the laboratory. On the other hand, orangutans have not only been recorded asusing tools in the wild (see, e.g., Van Schaik et al. ), but are also able to use themin the lab. While, in the categorization studies discussed, the gorilla was unable toreach the criterion for transfer for the intermediate category (see Vonk andMacDonald ), the orangutans were more successful, though their success wasmoderate (see Vonk and MacDonald ).

A potential objection lies in the fact that other non-human primates seem capableof basic level categorization. For instance, vervet monkeys produce different alarmcalls for different predators: eagles, leopards, and snakes (see Cheney and Seyfarth). These three categories would be basic level for humans. And, even moredamaging for the suggested explanation, vervet monkeys are certainly not tool-usinganimals. Thus, or so this putative counterargument would go, as a non-tool-using species is able to form basic level categories, the chimpanzee’s ability to formbasic level categories is not related to the chimpanzee’s tool-using abilities. Thisargument is less than convincing for several reasons. First it is important to note that,although vervet monkeys may have (proto-)concepts at basic category level, theseproto-concepts correspond to affordances. Indeed, it is because eagles, leopards, andsnakes trigger highly different responses in vervets (respectively leaving the canopyand going down in the trees, climbing up to the canopy, and collective mobbing) thatthey are distinguished in alarm calls as well. There is more, however. The alarm callsthemselves are innate, as they are identical in adults and infants, although infantsseem to overproduce them at first. Note, however, that this overproduction isstrongly constrained: eagle calls will be produced for other (non-predatory) birds,leopard calls will be produced for other (harmless) quadrupeds, and snake calls maybe produced for, for example, a stick. This suggests that the categorical discrimin-ation between eagles, snakes, and leopards is also innate and merely needs fine-tuning through experience. In other words, for vervet monkeys, eagles, snakes, andleopards are inborn affordances (or inborn proto-concepts), and the ability todistinguish between them is no indication of a wider-ranging ability to form basiclevel concepts.

So, to sum up, creatures that, like humans and chimpanzees, are able to categorizeat the basic level are also able to process visual information at the global level (forexample, to see the shape rather than the details), which allows them to discriminatebetween objects at that level. (Remember that categorization depends on discrimin-ation. And discriminative abilities are clearly perceptual in nature.) The categoriesthat chimpanzees form at that level are, however, affordances, just as are the more


comprehensive categories that other primates can form. So why did chimpanzees, butnot other apes (with the potential exception of orangutans), acquire the ability toprocess visual information at the global level? Our suggestion is that, just as humans,chimpanzees are tool-users, and that, this being so, they need a finer-grained level ofcategorization of both objects and situations (as affordances) than do non-tool-usersin order to adapt their tool-using behaviours to their current needs.

This, then, in a nutshell, is the answer to the first question: the reason why onlyhumans and chimpanzees—in our present state of knowledge—give evidence of basiclevel categorization is because only humans and chimpanzees (with the same proviso)are able to treat visual information at the global level, bypassing details in favour ofglobal shape. And the reason why only humans and chimpanzees are able to treatinformation at that level is that both species are regular tool-users, and in need of finer-grained categorization than is the case for other primates.

So let us now turn to the second question: why are humans the only species able toentertain strongly decoupled thoughts? I would like to begin by pointing out that,although humans and chimpanzees are able to treat visual information at the globallevel, favouring shape over details, only humans show a strong preference for thatlevel of visual processing. Chimpanzees do not show such a preference. If, as arguedabove, processing visual information at the global level allows categorization andconceptualization at the basic level, having a preference for that level of visualprocessing should lead to a conceptual explosion. This is because there are anenormous number of categories at the basic level, much more than there are at thesuperordinate level. A preference for global processing should lead to a much greaternumber of categories linked to a greater number of concepts. However, this is clearlynot enough in itself to explain why these concepts can be used in a stronglydecoupled way, given that chimpanzees, who are also able to have concepts andcategories at that level, use them at best in a weakly decoupled way. Thus, havingbasic level concepts is not in itself linked to the ability to use them in a stronglydecoupled way.Here, I want to follow two (eventually convergent) paths: first, I want to argue that

it is not so much the ability to form basic level concepts that is crucial for strongdecoupling, but rather the overall number of concepts that one has; and, second,I want to argue that the preference for global visual processing and the conceptualexplosion that it triggers can be explained by the very different needs of chimpanzeesand humans. So let me begin with why the number of concepts rather than theirbeing basic level is important. Here, I would like to come back to language acquisi-tion. As Bloom () notes, it is a robust finding of language acquisition studies that,for syntax to take off, a minimal size of vocabulary (roughly over words) has to bereached. This suggests that hierarchical syntax appears when the size of the child’slexicon is such that the simple concatenation of two elements (for example, a verb


and a noun59) is not sufficient any more to accommodate the child’s communicativeintentions. In other words, the emergence of syntax is dependent on the size of theavailable lexicon, and this suggests that syntax emerges at first as a self-organizationalprocess, linking words, where they were previously more or less entirely autonomous(see Chapter , for a more detailed discussion of syntax).

I would like to suggest that very much the same goes for thought. As we have seen,Fodor’s Language of Thought (Fodor , ; Fodor and Pylyshyn ) issyntactic as well as semantic. Concepts provide the basic semantics, while syntaxprovides compositionality. The preference for global visual processing over localvisual processing is relevant here, as the basic level is certainly the level at which veryyoung children most readily categorize objects. It is also relevant because, as saidbefore, this is the level at which there is a huge number of categories to be formed.Thus, having such a perceptual processing preference is enough to ensure that onewill fairly quickly reach a number of concepts sufficient to trigger hierarchical syntaxas a self-organizational process. And syntax, as we shall see, is relatively indifferent tosemantics. What is important for syntax is to have discrete units to combine, butwhat these units mean is not central (although semantics is obviously necessary tohave coherent and organized thought processes; however, syntax is involved as wellin those thought processes that seem or are deviant60). The very fact that syntax is infact at least partly detached from semantics is enough to explain the human propen-sity for strong decoupling. I would like now to follow the second path—the verydifferent cognitive needs of chimpanzees and humans.

Why should two species prima facie as near as humans and chimpanzees havedifferent cognitive needs? It has become commonplace to distinguish among speciesthose that are specialist (well fitted to their environment, but not very well able tosurvive in other environments) and those that are generalist (able to adapt to prettywell any environment in which they find themselves). While chimpanzees arespecialist, humans are generalist. Chimpanzees (and all other apes), while quitewell fitted to their environment, cannot live in any other different environment.61

By contrast, humans are generalist. Generalist species can be so for different reasons:their needs may be so restricted that they can be satisfied by a wide array ofenvironments (this is the case, arguably, of that arch generalist species, the rat);they may reproduce so quickly and in such great numbers that natural selection can

59 It is important to note here that such simple combinations are characteristic of the utterances of apesengaged in animal language programmes. What is more, as we saw above, the lexicon of these animals isstrongly limited and seems to peak at between and words.

60 From that point of view, the existence of populations in which syntax is preserved, but withdisordered thought processes and/or with deviant or disorganized semantic abilities (e.g., schizophrenicor Williams syndrome patients), is significant. Note that, in these populations, there is a large lexicon, butthe semantic connections seem affected.

61 This is indeed why the destruction of their respective habitats has placed all non-human apes on thelist of endangered species.


do the job for them, as may be the case for many species of insects. However, humansare not quick to reproduce, do not produce a great number of offspring perfecundation, and neither have they restricted needs: indeed, given the long depend-ency of children on their parents for survival and given the huge energetic demandsof the human brain, they seem especially badly fitted to be a generalist species.Yet, there is no doubt that they are. The answer to that quandary is that they havefollowed a unique path to that generalist status: they are the only species to adapt toan extremely wide array of environments by devising new artefacts, including tools,and habitations with widely different features, and by being able to form represen-tations of their new environments very quickly through their conceptual abilities. Inother words, they are generalist because of their cognitive abilities.The very fact that humans are a generalist species in that specific sense has

important consequences regarding their concepts and why these concepts arestrongly, rather than weakly, decoupled. To see this, it is useful to go back to thenotion of affordance. As already discussed, the notion corresponds, in Gibson’s view(), to the opportunities for action that are available to a given organism in itsimmediate visual environment. Thus, one and the same environment will presentdifferent affordances for different species, and even different affordances for the sameorganism depending on its internal states (for example, whether it is (or is not)hungry, thirsty, looking for a mate, and so on). In other words, the same objects arepresent in the environment, but, depending on the nature of the organism (whether itis, for example, a leopard or a chimpanzee) and on the present internal state of theorganism, they will or will not be affordances (fruits will be affordances for a hungrychimpanzee, but not for a hungry leopard), and may be highly different affordances(a chimpanzee may see another member of his group as a rival for food when he ishungry and as a potential mate when he is satiated).Dretske () distinguished between what he called ‘simple seeing’ and ‘seeing

that’. The distinction is in fact grounded in the different verbal reports that can bemade of these two kinds of seeing. If some organism simply sees something, we candescribe what it does with a sentence where the complementizer is a noun phrase—for example, ‘John sees mushrooms’. If, on the other hand, John’s seeing is of theseeing that kind, the complementizer will have to be of the propositional clausevariety—for example, ‘John sees that there are mushrooms’. The second kind ofseeing, seeing that, involves categorization (and hence the possession of the relevantconcept), while the first, simple seeing, does not. In other words, you can ‘simple see’mushrooms without being able to identify what you see as mushrooms. But youcannot see that there are mushrooms without identifying what it is that you areseeing as mushrooms.62 Though Dretske clearly intended the distinction to apply

62 Note that the distinction is not relevant to discrimination as such.


between situations where there is or is not conceptualization of what is seen, there isno doubt that it can apply at the level of affordances as well. A thirsty (but nothungry) chimpanzee will see fruit, but will not see that there is food, while a hungryone will. There are, however, a few differences between affordances and concepts andthese differences have a lot of consequences, as we will now see.

A first important thing to note is that humans, as much as non-human animals,perceive affordances. Now, what we see (in a seeing that sense) in a visual scenedepends on what we are attentive to (as shown in the change blindness studies, seeSection ...). There are two sorts of attention: heterogeneous attention, whichdepends both on what there is in the environment and on the internal but non-volitional (for example, hunger) state of the organism; and endogenous attention,which depends on what there is in the environment but is largely under voluntarycontrol. We quickly alluded to the fact that the perception of affordances is a matterof heterogeneous attention. Hence, it is by definition limited to what is relevantto the satisfaction of the needs of the organism at a given time.63 By contrast,humans are also capable of endogenous attention, and endogenous attention canbe disinterested—that is, it can be entirely independent of the individual’s presentneeds. Why humans, and presumably only humans, are able to do this leads us backto the fact that humans are a generalist species in a cognitive sense. As such, a humanorganism cannot rely on her knowledge of the affordances present in her currentenvironment, because this will not be enough to ensure her survival (and the survivalof her descendants) in a new kind of environment. Rather, she will have to be able toabsorb knowledge about any environment whatsoever in which she might findherself. In other words, her cognitive abilities have to be disinterested in the sensethat they are not restricted to what is useful in the here and now. They have to besuch that they will allow her to understand in a quick and efficient way anyenvironment she might find herself in. While heterogeneous attention is alwaysdependent both on what is present in the environment and on the present needs ofthe organism, and hence is always directed, endogenous attention is dependent onlyon what is in the environment, and on what the organism wants to attend to, and thatmay be to grasp what is in the environment independent of its present use. Hence,endogenous attention can be largely non-directed. But non-directed endogenousattention makes sense only if it is accompanied by cognitive abilities allowing theindividual to make sense of her surroundings through processes of quick categor-ization and conceptualization, allowing her to accumulate knowledge about the

63 Note that, in the case of the apes engaged in animal language programmes at least, the needs of theorganism can be partly dissociated from basic organic needs, such as the urge to eat, drink, mate, etc. Thismay be due to the fact that these apes are strongly enculturated (see Segerdhal et al. ) or it may be acharacteristic of the species. Equally, it might be due to the fact that they are well fed and that their basicneeds are satisfied.


objects in the categories she has formed. This is where a strong preference for globalprocessing of visual information comes in as a crucial component in such abilities.Here, to avoid any accusation of teleological reasoning,64 it is useful to remind the

reader that chimpanzees (or at least some of them) are capable of global processing ofvisual information (see Hopkins and Washburn ). As they share this ability withhumans, a reasonable assumption is that the last common ancestor between humansand chimpanzees also had this ability. In other words, this ability for the globalprocessing of visual information is a homologous feature of both humans andchimpanzees, the result of their inheritance from their last common ancestor. Ifthis is the case, natural selection had the relevant material to act upon and to select astrong preference for global processing over local processing at some point or otherin the hominin history. There is no incontrovertible way of determining when thismajor change occurred. However, given the sudden upsurge of technological changethat accompanied the emergence of modern humans after millennia of relative stasis,and the rather legitimate hypothesis that this was linked to better conceptual abilities,it makes sense to assume that this was a late development that occurred with thereorganization of the brain in modern humans (see Boeckx and Benitez-Burracoa,b; Benítez-Burraco and Boeckx ,).

Thus, in a nutshell, the answer to the second question (why are humans the only speciesable to entertain strongly decoupled thoughts) is that humans, by contrast withchimpanzees and all other apes, are a generalist species that relies on its cognitiveabilities to survive in widely different environments. This led to the selection, on thebasis of the homologous ability for global visual processing, of a strong preference forthat level of visual treatment, allowing humans to form huge collections of concepts, farbeyond the affordance proto-concepts to which apes are limited. Not being affordances,these concepts could be deployed in the absence of their referents. This conceptualexplosion triggered a self-organizational syntax, allowing humans to link conceptstogether in thought. The fact that syntax is relatively indifferent to semantics movedthoughts further away from the present surroundings. Thus, both the nature of humanconcepts (which are not limited to affordances) and the emergence of syntax explainthe ability for strong decoupling in humans.

It is important to note that, in addition, humans are not limited to concepts formedat the basic level. They can also form concepts at the subordinate level, and at thesuperordinate level. Though these superordinate concepts may correspond to affor-dances, they need not. Additionally, just as is the case at the basic level, even thosesuperordinate concepts that do correspond to affordances can be used in a stronglydecoupled way.

64 Or argument by design, beloved by Creationists.


Humans are also able to form concepts for non-perceptible entities—for instance,inner mental states—and not only for emotions, which are arguably perceptible fromfacial expressions, but also for knowledge and beliefs, which are not (and indeedwhich are not even clearly linked with any phenomenological state). They can alsoform concepts for non-existent entities—for example, UNICORN—and even forimpossible things—for example, SQUARE DOME. These abilities, which are inpart due to syntax and semantic compositionality, would open whole new areas ofcognition to humans. But a new cognitive paradigm, embodied cognition, has castdoubts on the idea of a disinterested, or strongly decoupled, conceptual apparatusin humans.

. . EMBODIED SEMANTICS

The discovery of mirror neurons in the s has triggered new views about conceptsand the lexicon, which we will now examine briefly. Mirror neurons are neurons inthe ventral premotor cortex of macaque monkeys that fire both when an agentperforms an action (for example, grasping) and when it sees another agent performit. They were discovered by Rizzolatti’s team in Parma (see Gallese et al. )through electrophysiological recording of single neurons, and it was suggested thattheir mirror function contributed to action recognition. Given that electrophysio-logical recordings of single neurons are not ethical in humans, the evidence for theexistence of mirror neurons in humans is mostly indirect (though see Keysers andGazzola , for single neurons recordings in epileptic patients undergoing pre-surgical investigations). Mirror neurons gained in popularity, and the relativelymodest initial interpretation in terms of action recognition was developed towardsclaims to the effect that they play a major role in social cognition (allowing thefaithful imitation that seems to be specific to humans, empathy, theory of mind, andso on) as well as in language evolution (see Arbib ). One obvious objection isthat mirror neurons have been evidenced in macaques, animals who do not seem tobe extremely good at higher social cognition, including imitation and Theory ofMind (though as primates, they are social animals) and who clearly are non-linguisticanimals. Ramachandran () defended the view based on the idea that the mainforce in the evolution of both human cognition and human language was imitation,which is strongly facilitated by mirror neurons. As to the absence of imitation inmacaques (who undoubtedly have mirror neurons), the suggestion is that humanshave a much greater quantity of mirror neurons, which explains the discrepancy.While there is no clear evidence that this is the case, the debate has shifted inthe sense that current hypotheses claim that the best evidence for mirror neuronsin the human brain (and presumably of the link to language evolution) lies in theembodiment of semantics (see, e.g., Gallese and Lakoff ).

Embodied semantics

Embodied semantics is one aspect of the wider paradigm of embodied cognition,which claims that cognition is intimately linked to perception and action, so intim-ately linked, in fact, that it makes no sense to maintain the classical distinctionbetween cognition, on the one hand, and perception and action, on the other.Regarding semantics, the main thesis concerns the lexicon: the idea is that wordsfor concrete or perceptible entities or actions are intimately linked to the corres-ponding systems in perception and action. Thus, this would be true for colour wordsthat would activate those parts of the brain that are linked to colour perception, whileodour words would activate the olfactory cortex, and so on (see, e.g., González et al., Moscoso del Prado Martín et al. , and Pulvermüller and Hauk forresults that support the hypothesis). The most productive domain of investigationhas been linked to action words (mostly verbs), which are predicted to activate thepart of the motor system that is specifically linked to the effector used to perform theaction (for example, the hand, the arm, the leg, the foot, the mouth, and so on). Thefirst major results were presented by Hauk et al. (), who used fMRI recordings(scans of the brain while the participant is involved in a given task, showing whichbrain regions are differentially activated during this task) and showed that bothperforming an action with a given effector and listening to an action word involvingthat effector would activate similar areas of the motor strip.65 The authors noted(Hauk et al. : ): ‘It may be that multimodal mirror neurons contributing toboth language and action are the basis of the observed overlap in cortical activation,’making clear the link between the embodied semantic hypothesis and mirrorneurons. It should be noted, however, that, while these results show a link betweenactionwords and themotor cortex, such a link is far from being surprising and is not initself sufficient to support a major involvement of the motor system in lexical seman-tics. This is because the activation of the motor cortex could be the result of the lexicalinterpretation process (for example, a mental imagery process) rather than a part of it.Here, a crucial part of the story is time course of the activation because interpret-

ation is very fast (it occurs in the first ms after word onset). fMRI enjoys greatprecision as far as localization of the activation is concerned, but is much less preciseas far as its timing is concerned. On the other hand, EEG is temporally precise, andHauk and Pulvermüller () were able to show that indeed activation of therelevant part of the motor cortex occurs within ms of word onset. This resultwas reinforced by an interference study done by Boulenger et al. () in whichparticipants were asked to perform a grasping movement while listening to an actionword, which was presented either before movement onset or during the ms afteronset. While presentation before movement onset had a facilitatory effect, presenta-tion during the first ms after onset had an interference effect. The same team

65 While the overlap between the regions activated during both tasks was far from perfect, it wasnonetheless significant.


(Boulenger et al. b) completed these results by a paradigm in which words werepresented both visually and subliminally during the preparatory period for a reachingand grasping movement. EEG measures showed a decrease of the readiness potentiallinked to action as well as an interference effect for action verbs as opposed toconcrete nouns. Finally, it was shown (see Boulenger et al. a) that patientswith Parkinson’s disease (a neurodegenerative disease that primordially affects themotor system) were impaired in a lexical decision task66 for action words but not forconcrete words, when not under medication. Under medication, their performancewas similar to that of typical controls.

All these results seem to support a strong conclusion to the effect that the motorsystem is automatically activated on presentation of action words and, indeed, plays acentral role in their lexical interpretation. Nevertheless, there are limits to the studiespresented, the most obvious one from a linguistic point of view being that, in all ofthem, the words were presented in isolation. This is a dubious choice from anecological point of view, because words usually occur in utterances correspondingto sentences. Additionally, it seems to be an important part of the story that theactivation of the motor system should occur automatically, regardless of the linguisticcontext, if indeed the motor system is crucially involved in lexical interpretation.Thus, testing whether action verbs activate the motor system regardless of thelinguistic context in which they occur seems to be crucial. And a rather obviouslinguistic environment in that regard is a negative sentence. A first study was done in by Aravena et al., using a new paradigm, the grip force sensor.67 Aravena et al.compared variations in grip force while hearing three types of sentences: positivesentences with action verbs; negative sentences with action verbs; positive sentenceswith non-action-related nouns. There was a significant increase in grip force forpositive sentences with action verbs, but no increase for the two other types ofsentences. A similar result was found for action verbs embedded under volitionverbs (for example, ‘John signs the contract’ versus ‘John wants to sign the contract’).Again (see Aravena et al. ), there was a significant increase in grip force for thenon-embedded action verbs, but no increase for the action verbs embedded underverbs of volition.

All these later studies show that motor system activation is not automatic, whichsheds doubt on the notion that it is a crucial part of their lexical interpretation. Thisdoubt is reinforced by studies using TMS.68 Papeo et al. () have shown that

66 In a lexical decision task, participants are asked to indicate for both words and pseudo-words whetherthey are words.

67 The grip force sensor is a small sensor that participants hold in a precision grip (between the thumband the index) and that registers minute variations in the force of the grip. It has been shown to be a goodand simple method to investigate motor activation during action word processing (see Frak et al. )

68 TMS (Transcranial Magnetic Stimulation) is used to stimulate small regions of the brain. If the regionin question is supposed to be involved in a given cognitive process, an interference effect is predicted.

Embodied semantics

perturbations induced by TMS on the motor system have no effect on action wordprocessing. Finally, a study in neuropsychology, using patients with lesions in therelevant brain areas, has shown that these patients are not impaired in action wordprocessing, suggesting that the role of the motor cortex in the interpretation of actionwords is ‘complementary rather than central’ (Arévalo et al. : ).Thus, while the activation of the motor system by action verbs in some linguistic

contexts is in need of an explanation (and, here, clearly, further research is needed),there is no reason to adhere to the rather extreme tenets of embodied cognition.Indeed, such phenomena might be explained, according to distinctions already laiddown, in terms of the deployment of parts of the conception associated to theconcept, rather than in terms of the deployment of the concept itself (that is, lexicalsemantics is not directly involved in the process), as shown by Arévalo et al.’s study.Hence, it would seem that human concepts are indeed strongly decoupled, and thismay be the basis of further cognitive differences between human and non-humanprimates, as we will now see.

. . SPECIFICITIES OF HUMAN COGNITION

One interesting area here (and I will limit myself to it for reasons of space) is mindreading. Mind reading, otherwise called ‘Theory of Mind’, is the ability to understandand predict the behaviour of others through the attribution of mental states to them.In humans, the hallmark of mind reading is taken to be the ability to pass the so-called false belief test. The false belief test is a simple paradigm, based on a displace-ment story: a character has an object that she puts in a given location. Then sheleaves. In her absence, a second character takes the object and puts it in anotherlocation. The first character comes back. The participant is asked two questions:

• Where is the object now (a control question to make sure that the story has beenunderstood)?

• Where will the first character look for the object (the test question)?

The correct answer to the test question is that she will look where she first placedthe object not where it is now. In other words, she will look where she (falsely)believes the object to be, rather than where it actually is, unbeknownst to her.69 Thus,we can predict and understand others’ behaviour not so much from what we know tobe the case, but from what they think to be the case, provided that we can correctlyattribute beliefs to them, however different these beliefs may be from our own.

69 In other words, as rightly noted by Mercier and Sperber (), where the object is now is irrelevant.What is relevant is where the first character initially put it.


Human children can pass the standard false belief test (which is rather heavilylanguage-dependent) by to years of age. There is, however, reason to think thatthey may be able to pass it earlier, and children as young as months have passednon-verbal tasks deemed to be equivalent to the false belief task. On the other hand,non-human primates (chimpanzees are the only species that has been tested) do notpass it, though they may be able to understand SEEING. There is a strong debateabout chimpanzees’ (and more generally non-human animals’) abilities for mindreading (see Lurz for a good overview). But, though the jury is out on SEEING,no one seems ready to defend their ability to understand the concept of BELIEVING.

So here we have two highly social species, humans and chimpanzees, who haveapparently strongly different abilities to mind read, while mind reading is arguably amajor social cognitive ability. The obvious question is why this should be so. Let ussuppose for the sake of the argument that chimpanzees actually understandSEEING. Where other animals are looking, and, hence, what they are seeing, isimmediately perceptible.70 Seeing what another animal sees (which, being real, isimmediately available to perception) may indeed be readily available to the apes. Onthe other hand, BELIEF is quite another matter, especially when false belief isconcerned. Not only has belief to be deduced (it is not immediately accessible toperception), in the case of false belief, the state of affairs that is the object of the beliefis not available either. What is more, while SEEING can be understood on the basis ofsimple seeing (with no need to attribute concepts to others), BELIEF rests on thecomplex syntax of the complementizer clause (for example, the first character—inthe false belief task—believes that the object is where she put it).

A legitimate explanation for the different mind-reading abilities of chimpanzeesand humans may thus be, quite simply, that they have different conceptual appar-atuses. Chimpanzees are unable to conceptualize entities that they cannot perceive,and the limitations of their conceptual apparatuses have not allowed them to developa syntax sufficient to allow them to attribute propositional attitudes (such as belief)to others.

. . CONCLUSION

In conclusion, in the present chapter, I have argued that non-human animals,including great apes, have conceptual apparatuses that are not on a par with thoseof humans. While humans can categorize a single object in different ways, allowingthem to form rich conceptual hierarchies, animals seem much more restricted.Additionally, their concepts seem to be, at best, available for weakly decoupled use,

70 Indeed, a good number of animal species, notably domestic species, have been shown to be capable ofgaze following (see, e.g., Call et al. ; Kaminski et al. ).

Conclusion

not for the strongly decoupled use that is open to humans. In other words, animalconcepts seem restricted to affordances, while this is not the case for humanconcepts. This may come from the fact that humans are a generalist species, ableto survive in widely different environments, not through their physical or reproduct-ive abilities, but through their cognitive abilities, which allow them to make sense ofwhatever environment they may find themselves in. While human concepts areextensional and are thus (pace Machery ) neither prototypes, exemplars, ortheories, nevertheless they give access to rich information of different nature aboutthe objects that fall under the corresponding categories. It is here that prototypes,exemplars, and theories come in.The incommensurably richer conceptual apparatuses of humans led to the emer-

gence of syntax as a self-organizational system. This allowed a potentially infiniterange of thoughts and allowed humans to develop conceptual abilities far beyond thereach of even chimpanzees. The emergence and nature of syntax will be the maintopic of Chapter .


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