ideas which according to Potter’s own account ‘were so far from Russell’s way ofthinking that he never understood what they were’.

In a letter to Russell of June , Wittgenstein remarks that Principia’sReducibility |− :(∃f ): φx ≡x f !x ‘is only a schema, and that the real Pp ought to be|− :. (φ):(∃f ): φx ≡x f !x, and where would be the use of that?’. Potter writes that ‘Thefirst kind of ambiguous assertion, although strictly incorrect, is innocuous because byprefixing the formula with a universal quantifier we can turn the real variable intoan apparent one. The second kind is not innocuous, because no correspondingmanœuvre is available to us’ (p. ). Restoring schematic type indices, Potter seemsto have the following in mind: ‘|− :. (φ(t )):(∃f (0)): φ(t )x0 ≡x0 f (0)!x0 ’. This cannot work,since Principia does not count φ(t )x0 as well formed for t > . Potter is quite right that‘whether a variable is typically ambiguous has nothing to do with whether it is realor apparent’ (p. ). He thinks that Wittgenstein was ‘fumbling’ towards formu-lating an objection against using schematic type indices to express that a theoremholds in all the types. He also thinks Wittgenstein was ‘inept’ in failing to object totheir use in the quantification theory of * of Principia (p. ). But Potter missesWittgenstein’s intent. Comprehension, not quantification theory, is precisely whatmakes logic a genuine science. For comprehension to do its work, it must (unlikequantification theory) use schematic letters for wffs (or in modern cumulative types,it may use free variables and a rule of uniform substitution). Wittgenstein objects tothe ineliminable schematic φ in the comprehension principle of Reducibility becausehe holds that logic is contentless.

These many issues do not undermine the book. Indeed, no scholar of Russell orWittgenstein can afford to miss contributing to the fiery debate they should provoke.I shall therefore end with a curiosity. Potter says that Wittgenstein ‘read little beyondPrincipia’s Introduction’ (p. ), and was so ‘little engaged’ with the formal logicof Principia that some of his comments about it ‘are inept in the extreme’ (p. ). Incontrast, he says that Wittgenstein had a ‘profound engagement with Frege’s con-ception of logic’ (p. ). Yet Potter thinks that Frege’s published works (even theinformal Grundlagen) had comparatively little impact on Wittgenstein and that he wasable to ‘absorb’ from their ‘few visits’ important insights implicit in Frege’s Post-humous Writings (pp. , ). Potter seems to mean that Wittgenstein’s engagementwas neither with Frege’s bewildering technical philosophical logic of extension,number, ancestral, etc., nor with the presentation of these concepts in Principia, butwith the philosophical parts of Grundgesetze’s Introduction (concerning, for example,assertion and truth). What is now curious is that Potter unintentionally leaves theTractatus itself ‘inept in the extreme’.

University of Iowa G L

Real Essentialism. B D S. O. (London and New York: Routledge, .Pp. xii + . Price £..)

David Oderberg’s new book is, as far as I know, the only comprehensive book-length exposition, defence and application of Aristotelian essentialism written from

The Philosophical Quarterly Vol. No. July ISSN – doi: ./j.-.._.x

© The Author Journal compilation © The Editors of The Philosophical QuarterlyPublished by Blackwell Publishing, Garsington Road, Oxford , UK, and Main Street, Malden, , USA

The Scots Philosophical Associationand the University of St Andrews

the perspective of modern analytic philosophy. It is a major intellectual achieve-ment, which will repay close reading and re-reading by friends and foes ofessentialism alike. The ‘real’ in the book’s title is there to mark the distinctionbetween this truly Aristotelian conception of essence and that emanating fromversions of essentialism inspired by the ‘possible worlds’ approach to metaphysicalmodality, whose modern fountain-head was Saul Kripke’s Naming and Necessity.Oderberg’s approach to essence has something in common with that of Kit Fine,whose work he cites with approval and discusses extensively, but he is most stronglyinfluenced by the original texts of Aristotle and Aquinas. He is above all concernedto defend essentialism in the context of a thoroughgoing commitment to hylemorphism

– the doctrine that all substances are combinations of matter and form – and thus toa fundamental ontology of substance and accident. Although he recognizes, withAristotle, a ‘relative’ notion of matter, he is also committed explicitly to the notion ofprime matter, as well as to the Aristotelian association of matter with potentiality andform with actuality.

The book moves from very general metaphysical and epistemological problemsconcerning the nature and knowability of essence, through more specific issues inontology concerning substance, matter, form, identity, existence, powers, laws,accidents and properties, and finally to the application of hylemorphic essentialismto questions in the philosophy of nature, especially in the field of biology. The longchapter on biological species, which is extremely well informed from a scientificpoint of view, is in itself a major contribution to the metaphysics of biology, pre-senting an important challenge to much contemporary scientific and philosophicalthought concerning biological taxonomy. The book ends with a chapter on humanpersonhood, defending once more an Aristotelian dualism of matter and form, quiteopposed to any kind of neo-Cartesian psychophysical dualism but equally opposedto mainstream contemporary physicalism in the philosophy of mind.

In a short review, it is impossible to do justice to this book’s richness of ideas andarguments. Oderberg, although he draws extensively on Aristotelian insights, is ahighly original thinker in his own right and an extremely independent one. He nevershies away from or waters down an opinion merely because it is currently unfashion-able, but always proceeds resolutely in whatever direction he takes the force ofevidence and argument to lead him in. He is adamant that a priori metaphysicalconsiderations have an important bearing on which scientific theories we should beprepared to endorse, but at the same time he is no mere armchair philosopher,insisting that empirical enquiry is indispensable for any adequate knowledge of theessences of things existing in the natural world. In what remains of this review, Ishall simply register some doubts about certain aspects of Oderberg’s position, partlywith a view to conveying more fully the flavour of his approach. None of thesedoubts, however, diminishes in the least my estimate of the importance of Oder-berg’s overall achievement, which is a remarkable one. I should add that the doubtsmay well reflect failures on my own part to understand the subtleties of Oderberg’sposition, more than any genuine flaws in his views or arguments.

On the matter of essence, Oderberg dissents from Fine’s view that, for example,it is no part whatever of Socrates’ essence that he is distinct from the Eiffel Tower or

BOOK REVIEWS

© The Author Journal compilation © The Editors of The Philosophical Quarterly

is the member of singleton Socrates (the set whose sole member is Socrates).Oderberg maintains instead that these are ‘virtual’ parts of Socrates’ essence, givingas his reason for this that ‘[Socrates’] essence – being a rational animal – virtuallycontains the categories of being a material object and being an entity of some sort or other, towhich necessary distinctness and singleton membership apply, respectively, as partsof these essences formally stated’ (p. ). I confess that I do not entirely understand thisline of reasoning, because while I am happy enough to say that it is part of Socrates’essence that he is a material object and that he is an entity of some sort or other, Isimply do not see how this provides any essential connection at all between Socratesand the particular entities in question – the Eiffel Tower and singleton Socrates –nor, indeed, even with the sorts of things that they are (a building and a set,respectively).

The problem is that I do not really understand Oderberg’s distinction betweenparts of an essence ‘formally stated’ and ‘virtual’ parts of an essence, notwith-standing his attempt to explain the latter notion as follows: ‘being F is a virtual partof the essence G of an object x if and only if x’s being G logically presupposes x’sbeing F’ (p. ). Does Socrates’ being an animal, or his being rational, ‘logicallypresuppose’ his being distinct from any building and, in particular, being distinctfrom the Eiffel Tower? Oderberg tells us that he understands logical presuppositionto be ‘a species of entailment, according to which the thing entailed is implicit inthe thing that entails’ (p. , n. ). This seems, appropriately enough, to exclude theweak sense of ‘entail’ in which any necessary truth is entailed by any truth whatever,and thus one obvious but irrelevant sense in which ‘Socrates is an animal’ clearlydoes entail ‘Socrates is distinct from the Eiffel Tower’ (assuming the latter to be anecessary truth). But unfortunately I do not understand in what sense of ‘implicit’ itcan be at all plausibly said that ‘Socrates is distinct from the Eiffel Tower’ is implicit

in ‘Socrates is an animal’, nor therefore the sense in which Oderberg himself takesthe ‘entailment’ to hold. I can see how the essence of an animal and the essence ofiron might very plausibly be supposed to be such that no animal can be identical withany building made of iron, and hence why Socrates (who is essentially animal) must

be distinct from the Eiffel Tower (which, let us suppose, is essentially made of iron).But then this necessary truth seems to flow from two independent essences takentogether, not from Socrates’ essence taken by itself.

I also, and perhaps more importantly, have doubts about Oderberg’s ownpreferred characterization of Socrates’ essence, ‘formally stated’, which (as we havejust seen) he takes, in true Aristotelian style, to be rational animal. Oderberg is fullycommitted to the Aristotelian notion of essential definition per genus et differentiam. Tostate something’s essence, on this view – to say what it is – is always to say what kind

of thing it is and in what respect it differs specifically from other things of that kind,thereby identifying which species of that kind (or genus) it belongs to. Unsur-prisingly, Oderberg is, as a consequence, very favourably disposed towards ataxonomy of nature along the lines of the tree of Porphyry, however old-fashionedthat might seem to modern scientists and especially to evolutionary biologists (whosesystems of classification he severely criticizes in his interesting chapter on thesubject). I only say here that I find the suggestion that a natural-kind term, or its

BOOK REVIEWS

© The Author Journal compilation © The Editors of The Philosophical Quarterly

referent, can be defined per genus et differentiam deeply problematic, for logical reasons.This, basically, is because I do not believe that complex terms of the form ‘A that isF’, where ‘A’ is a kind term and ‘F’ is a predicate, can properly be regarded asgenuine semantic units with an identifiable semantic value or reference. Thus, forexample, ‘human’ and ‘animal that is rational’ do not, very arguably, behave logic-ally in the same way, whence it is difficult to maintain that the latter in any senseprovides a ‘definition’ (even a ‘real’ or ‘essential’ definition) of the former – a generalpoint, incidentally, made long ago by another philosopher broadly sympathetictowards Aristotle, Peter Geach, who said that complex terms of this form are ‘a sortof logical mirage’.

An indication, perhaps, of the deep water that Oderberg seems in danger ofgetting into through his enthusiasm for definition per genus et differentiam is provided byhis response to the question of what we should say were we ostensibly to discoverother animal species besides ourselves to be rational beings – dolphins, perhaps, oralien creatures from Mars. His answer is that we would in fact be obliged to regardthese creatures as humans, like ourselves, and thus not in reality members of adifferent animal species (see pp. –). This is because they would be, like us,rational animals, which he takes to be what humans, by definition, are. My ownintuitions in such matters accord entirely with those of Locke, as displayed in hisdiscussion of the famous example of the ‘rational parrot’. This parrot would be aperson, surely, but not a man. Like Locke, I do not think that ‘person’ is a biologicalterm at all, in contrast with ‘man’ (or ‘human’) and ‘parrot’, which denote kinds ofliving organism. Being animal is, very arguably, at least part of our nature (or‘essence’), as is being (potentially, at any rate) rational. But I think it must be wrong toconnect these two aspects of our nature in the manner in which Aristotle andOderberg do, through their strict adherence to the doctrine of definition per genus et

differentiam – a doctrine which obliges us to regard one of these aspects as being agenus and the other a differentia which determines a unique species of that genus. Ifindeed we belong essentially to any species or kind of animal, then the kind ofanimal that we actually are – human – is surely not the same, by any reasonablestandard, as that of any putatively rational animal whose natural bodily form isavian or cetacean, let alone extra-terrestrial. Hence ‘human’ surely cannot simply bedefined as ‘rational animal’. Rather, its proper application should take into accountspecific features of our distinctively mammalian, and more particularly primate,body-plan, life-cycle and behaviour. Perhaps, on the other hand, there is a broadersense of ‘human’, in which – were such a thing possible – we should admit as anequal to the company of humankind an intelligent and emotionally endowed robotor ‘cyborg’. However, ‘human’ even in this putative sense is, obviously, no moredefinable as ‘rational animal’ than is ‘human’ in the previously discussed sense.

On a more purely metaphysical note, I have already mentioned that Oderberg iscommitted to the doctrine of prime matter, which I confess to finding deeplymysterious, to say the least. Even more difficult, however, do I find his advocacy ofthe Thomist doctrine that it is matter that individuates a substance – that, for instance,Socrates is individuated by his matter (see pp. –). In response to the obviousobjection that Socrates is a substance of such a kind that he can exchange his matter

BOOK REVIEWS

© The Author Journal compilation © The Editors of The Philosophical Quarterly

with another substance of the same kind, such as Callias, Oderberg replies that it ishis matter indexed to a time that individuates Socrates, pointing out that no twosubstances of the same kind can share the same matter at the same time. But then Ido not see why the reference to matter does not simply drop out of Oderberg’saccount of the individuation of substances altogether, for it is equally true (veryplausibly, anyway) that no two substances of the same kind can exist in the sameplace at the same time – a claim which Oderberg himself is keen to endorse; so whydo we not just say that a substance is individuated by its place indexed to a time,given that this must be unique to any substance of its kind, with the advantage that asubstance’s place is much easier to identify than its matter? In fact I do not thinkthat we should say this, because a substance’s place at a time is, in general, entirelyaccidental – but then, so too, typically, is its matter at a time: both proposalsaccordingly fail if, as I think is strongly arguable, an entity’s individuator must be athing or things on which it depends for its very identity. Furthermore, it also seemsplausible that places and times are themselves ultimately individuated by substances,which would make both proposals circular. For what it is worth, I do not think thatwe can ultimately say anything more informative than that each substance individu-ates itself, and indeed that this is one of the principal hallmarks of true substances, asopposed to entities of dependent kinds, such as accidents (‘tropes’) and events, whichare individuated at least partly by the substances bearing or participating in them.

Limitations of space here preclude further detailed discussion of Oderberg’sthoroughly fascinating and very fine book. But I can particularly recommend, forthose interested in such matters – as many metaphysicians presently are – his verywell informed discussion of powers and laws of nature, which raises importantobjections to many current accounts of these.

Durham University E.J. L

BOOK REVIEWS

© The Author Journal compilation © The Editors of The Philosophical Quarterly