1996 Hedstrom Swedberg Social Mechanisms

Social MechanismsAuthor(s): Peter Hedström and Richard SwedbergSource: Acta Sociologica, Vol. 39, No. 3 (1996), pp. 281-308Published by: Sage Publications, Ltd.Stable URL: http://www.jstor.org/stable/4194832Accessed: 14/08/2010 11:29

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ACTA SOCIOLOGICA

Social Mechanisms

Peter Hedstrom and Richard Swedberg Stockholm University

In this article it is argued that the search for 'social mechanisms' is of crucial importance for the development of sociological theory. With this concept - which is occasionally used in the sociological literature but has received little systematic attention - attention is called to an intermediary level of analysis in-between pure description and story- telling, on the one hand, and universal social laws, on the other. While the search for universal laws and grand theory has a great deal of appeal, we do not believe that this type of theorizing is likely to foster the development of a useful body of explanatory theory. Drawing on the heritage of Robert Merton and James Coleman, it is argued that the essential aim of sociological theorizing should be to develop fine-grained middle-range theories that clearly explicate the social mechanisms that produce observed relationships between explanans and explanandum. We provide a tentative typology of social mechanisms, and we illustrate our argument by showing that three well-known theories in sociology - the self-fulfilling prophecy (Robert Merton), network diffusion (James Coleman), and threshold-based behavior (Mark Granovetter) - all are founded upon the same social mechanism.

Peter Hedstrdm and Richard Swedberg, Department of Sociology, Stockholm University, S-10691 Stockholm, Sweden C) Scandinavian Sociological Association 1996

1. Introduction Even though the concept of 'social mechanisms' is occasionally used in the sociological literature, it has received little systematic attention. Our main ambition with this article is therefore to examine more closely the notion of mechanisms, in an attempt to evaluate its potential role in explanatory sociological theory. The main message of the article is that further advances of sociological theory call for explanations that systematically seek to explicate the generative mechanisms that produce observed associations between events.

It might appear obvious that every sociological theory, worthy of its name, should be explanatory. But upon closer examination, it turns out that what often goes under the rubric of general sociological theory, should more properly be viewed as conceptual or sensitizing schemes, and not as explanations proper. Much of Anthony Giddens's work, for example,

282 ACTA SOCIOLOGICA 1996 VOLUME 39

exemplifies this tendency (e.g. Turner 1986; cf. Giddens 1987). And according to Jeffrey Alexander, writing in Handbook of Sociology, sociology should pay less attention to 'explanation' and more to 'discourse' (Alexander 1988:78-81). In an insightful article by someone who has devoted most of his academic career to general social theory, Goran Therborn (1991:178) notes: 'Absent in or marginal to currently prevailing general sociological theorizing is any ambition to explain. Little interest can be found in contributing to answering questions like: Why do these people act in this way? Why does that social order change in that way?' The type of mechanism-based theorizing advocated here focuses exactly on these types of why-questions.

The focus on mechanisms advocated here should not be confused with a purely descriptive sociology that seeks to account for the unique chain of events that led from one situation or event to another. All proper explanations explain the particular by the general, and as will be demonstrated below, there are general types of mechanisms, found in a range of different social settings, that operate according to the same logical principles. Our vision of an explanatory sociology, contains an ensemble of such fundamental mechanisms that can be used for explanatory purposes in a wide range of social situations.

Given the present, practically non-existent state of serious discussion of the notion of mechanism in sociology, we approach our task in a somewhat roundabout way.' First, we briefly relate Robert Merton's discussion of the role of explanatory mechanisms in middle-range theorizing, and thereafter we consider two recent discussions of explanatory mechanisms and their role in the social sciences, by Jon Elster and Arthur Stinchcombe. This is followed by brief discussions of a number of topics that we believe need to be clarified and elaborated. These include the interdisciplinary nature of the concept of mechanism; the role of mechanisms in sociological explanations; and a critique of a variable-centered type of theorizing that is inherent in the approach. Thereafter we employ the work of Merton (1968) on the self- fulfilling prophecy, of Coleman et al. (1966) on the diffusion of a new drug, and of Granovetter (1978) on collective behavior, in order to illustrate our notion of a general social mechanism, namely that the same mechanism often underlies different phenomena and different sociological theories. The article ends with a brief typology of such social mechanisms.

2. The use of mechanisms in sociology Among the classics the term 'mechanism' is rarely used,2 even if the idea often is present.3 An explicit use of the concept of 'mechanism' does not seem to have appeared in sociology until after World War II. The most suggestive discussion of the concept is in our opinion to be found in the writings of Robert Merton, who brought together the idea of mechanism with that of middle-range theorizing (Merton 1967). Merton firmly rejected all attempts to develop general systems of sociological theory and instead advocated that sociological theory should deal with 'social mechanisms'.4 The point was to locate a middle ground between social laws and description, Merton said, and 'mechanisms' constitute such a middle ground.

Social Mechanisms 283

Merton defined social mechanisms as 'social processes having designated consequences for designated parts of the social structure', and argued that it was the main task of sociology to 'identify' mechanisms and to establish under which conditions they 'come into being', 'fail to operate' and so on (Merton 1968:43-44). Merton briefly discussed concrete mechanisms that determine reference groups, create dissonance, and articulate role-sets,5 but the most important contribution of his essay, in our opinion, was his view of mechanisms as elementary building blocks of middle-range theories.6

During the last few decades the emphasis on mechanisms that had played such a vital role in Columbia Sociology has largely been pushed aside by a resurgence of general social theories, on the one hand, and of a variable- centered mode of theorizing, on the other. A few successful attempts to develop sociological theory founded upon the notion of explanatory mechanisms can be found in the literature, but these represent the exception rather than the rule. Before discussing these efforts, however, we will outline part of the recent meta-theoretical discussion on the role of explanatory mechanisms in social theory. This discussion has been dominated by Jon Elster, though Arthur Stinchcombe has also made an important contribution.7

3. Elster and Stinchcombe on the use of mechanisms in social science Jon Elster's work has for some time been infused with a strong sense that it is imperative to use the notion of mechanism in the social sciences. Through mechanisms, Elster argues, it will be possible to bypass the old opposition between laws and description in the social sciences and to focus research on an intermediary and much more flexible level. A view that Elster attributes to French historian Paul Veyne is probably also held by himself: 'progress in the social sciences consists of knowledge of ever-more mechanisms rather than ever-better theories' (Elster 1989:173).

In his book Nuts and Bolts for the Social Sciences (1989), Elster gives the most complete account of what he means by this concept. He enumerates five things that a mechanism is not, and when taken together, these can be said to add up to a negative definition of the concept. They are the following: * First, causal explanations must be distinguished from true causal

statements. To cite the cause is not enough: the causal mechanism must also be provided, or at least suggested;

* Second, causal explanations must be distinguished from assertions about correlations;

* Third, causal explanations must be distinguished from assertions about necessitation;

* Fourth, causal explanations must be distinguished from story-telling; and * Finally, causal explanations must be distinguished from predictions.

Sometimes we can explain without being able to predict, and sometimes predict without being able to explain. (Elster 1989:4-8)

In Nuts and Bolts, as well as in other works, Elster gives a number of concrete examples of mechanisms, from the natural and the social sciences. As an example of a 'psychological mechanism', he mentions the example of


'sour grapes' or the fact that one often ceases to desire what one cannot get. There also exists an opposite tendency: 'forbidden fruits', which refers to a situation where one desires what one cannot get. Two other such opposing 'mechanisms', mentioned by Elster, are 'the bandwagon effect' and 'the underdog effect' (Elster 1993:13-15).8

That Elster's work on mechanisms is still at an early and evolving stage is, however, also clear. One indication of this is that he has, up until now, failed to give a formal definition of what constitutes a mechanism (see especially Elster 1989:3-10; 1993:2-3).9 Another is that he has changed his opinion of what characterizes a mechanism in general. While in Nuts and Bolts Elster says that mechanisms imply 'explanations of ever finer grain', in a later work he maintains that mechanisms, as opposed to laws, only have limited generality (Elster 1989:7; cf. Elster 1991:7-8).

Like Elster, Stinchcombe argues that 'we do not have a suffilciently supple armory of mechanisms for making social science theory', and the main purpose of his contribution to the current discussion of mechanisms is to help remedy this situation (Stinchcombe 1993:24). It is important to note, however, that Stinchcombe advocates a much more restrictive definition of mechanisms than Elster:

Mechanisms in a theory are defined here as bits of theory about entities at a different level (e.g. individuals) than the main entities being theorized about (e.g. groups), which serve to make the higher-level theory more supple, more accurate, or more general. (Stinchcombe 1991:367)

Examples that Stinchcombe uses to illustrate his definition include maximizing individuals (on the lower level) who create a market through their actions (on the higher level); and molecules (on the lower level) that under certain conditions turn into gas (on the higher level).

Unlike Elster, Stinchcombe seems mostly concerned with establishing what constitutes a purely sociological mechanism. While in economics, as well as in much of sociology, the analysis often starts with individuals and ends up with outcomes on a group level, there also exists another possibility for sociologists, according to Stinchcombe. This is to view a situation as a mechanism ('situational mechanism'; Stinchcombe 1993:28-30). Stinchcombe refers at this point of his argument to Erving Goffman's definition of a 'situation', where the general idea is that people monitor one another in public places and adjust their behavior to the situation at large.10

The works of Elster and Stinchcombe raise a number of questions that need to be examined more closely in order to arrive at a useful and sufficiently precise definition of a 'social mechanism'. One such question, to be discussed in the next section, is how the notion of mechanisms has been used in other sciences, from physics to economics. We can obviously only provide a first and incomplete sketch of what is a huge and difficult topic. Nonetheless, one interesting aspect of the notion of mechanisms is exactly its interdisciplinary nature and the prospect that sociology might be able to incorporate certain ideas about or types of mechanisms from the other sciences.


4. The concept of mechanism as used in other sciences In physics the word 'mechanism' is rarely used. One important reason for this is of a historical or accidental nature and has to do with the fact that in physics the word 'mechanism' is connected to the scientific world view of the 17th century (e.g. Dijksterhuis 1986). It should also be remembered that in the 19th century thermodynamics popularized the notion of a system, which is broader than that of 'mechanism/machine' and allows the analyst to choose the environment of the system according to the purpose of the study. The attempt to conceptualize all phenomena according to the elementary laws of mechanics became impossible after the emergence of field physics in the middle of the 19th century. From then on, the word 'mechanism' has been used sparingly in modem physics.

The 17th century notion of mechanism spread from physics and astronomy to a number of sciences - such as chemistry and biology - where the term 'mechanism' is still used, though with different meanings. The Cartesian notion that organisms can be conceptualized as machines turned out to be very useful and became central to a new biological philosophy called 'mechanism', which is usually contrasted to that of 'vitalism' or the doctrine that life cannot be reduced to mechanics (e.g. Beckner 1967). In the 19th centurlT the term mechanism was disconnected from the metaphor of the machine' and instead became linked to that of the system. 12

The concept of 'law' is only used occasionally in the biological sciences - typically in connection with genetics and on the understanding that they are never without exceptions. According to Francis Crick, who shared the Nobel Prize in 1962 for his discovery of the molecular structure of DNA, 20th century biologists prefer to think in terms of'mechanisms' and not 'laws'. The reason for this is that the notion of 'laws' is generally reserved for physics, which is the only science that can produce explanations based upon powerful and often counterintuitive laws with no significant exceptions. 'What is found in biology is mechanisms, mechanisms built with chemical components and that are often modified by other, later, mechanisms added to the earlier ones' (Crick 1989:138).

In the social sciences, the prevalence of explicitly stated mechanism- based explanations varies widely between the disciplines. These types of explanations are rarely used in history, sometimes in sociology, and quite frequently in economics and psychology. Particularly in cognitive psychology, the notion of mechanism plays a key role. The basic approach here is one of 'information-processing', where the cognitive process is divided up into different stages with special 'mechanisms'. To cite a well-known work, 'The information-processing approach [in cognitive psychology] assumes that perception and learning can be analyzed into a series of stages during which particular components ('mechanisms') perform certain transformations or recoding of the information coming into them' (Bower 1975:33).

Economists often see themselves as thinking in terms of mechanisms, as opposed to sociologists and historians, who are believed to be more interested in institutions (e.g., Schumpeter 1989:293). The one mechanism that economists relate most of their analyses to - their master mechanism, so- to-speak - is clearly the market, conceptualized according to marginal utility


theory. That the market can be seen as a 'mechanism' goes back to the 18th century, when economics (via e.g. Adam Smith) became influenced by the Newtonian-Cartesian worldview; and it has become so self-evident to contemporary economists that the market is a mechanism, that they often use the terms 'market' and 'market mechanism' synonymously.

The basic approach in economics, to repeat, is to analyze a phenomenon by relating it in some manner to the market mechanism. Much of neoclassical economics in the 20th century can be understood as an attempt to explain ever more aspects of the economic process through the mechanism of the market: production as well as consumption and distribution. Economists' talent for thinking in terms of mechanisms, however, often becomes clear to non-economists only when they go beyond the traditional boundaries of economics. Examples of this can be found in Hirschman's Exit and Voice (1970)13 as well as in much of Thomas Schelling's work (e.g. 1978).

As economists gradually have expanded the boundaries of their discipline to include a range of topics traditionally considered the domain of sociologists, such as the family and organizations, the difference between the disciplines to an increasing extent have come to concern the types of theories being used. One such difference, but by no means the only one, centers exactly on the importance attributed to explanatory mechanisms. Comparing labor market sociology with labor economics, Aage S0rensen has noted that most labor market sociologists think of theory

as having to do with which variables should be included in the equations and how these variables relate to other variables - and not as something which is about which mechanisms produce the observed associations in the variables. This is where there is a huge difference between sociological research and economic research in this area; and the difference is very much to the disadvantage of the sociologist. (S0rensen 1990:308)

5. The explanatory importance of social mechanisms The core argument of this article is that the identification and analysis of social mechanisms is of great importance for the progress of the sociological enterprise. But what exactly is a mechanism and why should we focus on mechanisms rather than on statistical associations or other forms of relationships between the entities of interest?

It is far from trivial to provide a precise, yet sufficiently general definition of a social mechanism that captures the essence of the concept. As suggested by philosopher of science Rom Harr6 (1970), one key defining characteristic of an explanatory mechanism is the function it performs in an explanatory account. When we have observed a systematic relationship between two entities, say I and 0, in order to explain the relationship between them we search for a mechanism, M, which is such that on the occurrence of the cause or input, I, it generates the effect or outcome, 0. The search for mechanisms means that we are not satisfied with merely establishing systematic covariation between variables or events; a satisfactory explanation requires that we are also able to specify the social 'cogs and wheels' (Elster 1989:3) that have brought the relationship into existence.


This generative view of causal explanations differs in important respects from the classic covering-law model as advocated by Carl Hempel and his followers (see Hempel 1942, 1962). According to Hempel, an explanation of an event entails subsuming the event under a general law. A satisfactory explanation therefore must specify the general covering law and the conditions which make the law applicable in the specific case.14 According to Hempel, deterministic laws are quite unlikely in the social and the historical sciences. The general 'laws' that can be invoked in the social sciences are instead of a probabilistic nature, i.e., they state that the occurrence of a particular event will come about with such and such probability if certain specified conditions are at hand.

Since this form of explanation simply entails applying a general law to a specific situation, the insights offered by the exercise are directly propor- tional to the depth and robustness of the 'probabilistic law'. If this law is only a statistical association, which is the norm in the social and historical sciences according to Hempel, the specific explanation will offer no more insights than the law itself and will usually only suggest that a relationship is likely to exist, but it will give no clue whatsoever as to why this is likely to be the case. Covering-law explanations in the social sciences therefore normally are 'black-box' explanations and they do not attempt to reveal any mechanisms that might have generated the observed relationships. We are inclined to agree with von Wright's position that it is better 'not to say that the inductive-probabilistic model [of Hempel] explains what happens, but to say only that it justifies certain expectations and predictions' (von Wright 1971: 14).15

The main reason for advocating explanations that directly refer to generative mechanisms is, in our opinion, that they provide (or encourage) deeper, more direct, and more fine-grained explanations. The search for generative mechanisms consequently helps us distinguish between genuine causality and coincidental association, and it increases the understanding of why we observe what we observe.

The role that the search for mechanisms plays in distinguishing between spurious and real associations can be illustrated by the recent controversy surrounding possible health effects of electromagnetic fields. Some epidemiological studies have found an empirical association between exposure to electromagnetic fields and childhood leukemia (see Feychting & Ahlbom 1993). However, the weight of these empirical results is severely reduced by the fact there exists no known biological mechanism that can explain how low-frequency magnetic fields could possibly induce cancer (ORAU 1992). According to Bennett (1994), it is furthermore extremely unlikely that a mechanism will ever be found, because such a mechanism would have to violate well-established physical principles. The lack of a plausible mechanism increases the likelihood that the weak and rather unsystematic empirical evidence reported in this epidemiological literature, simply reflects unmeasured confounding factors rather than a genuine causal relationship (Hedstrom 1994a).

The distinction between black-box explanations and explanations that refer to explicit and generative mechanisms can be illustrated in more general terms with the following example that is adopted from the work of


philosopher of science and physicist Mario Bunge (1967). Assume that we have observed a systematic (non-random) relationship between two types of events or variables, I and 0. The way in which the two sets of events or variables are linked to one another is expressed with the mechanism, M:

I L1 0

WVhat characterizes a black-box explanation is that the link between input and output, or between explanans and explanandum, is assumed to be devoid of structure or, at least, whatever structure there may be, is considered to be of no inherent interest (perhaps because it cannot be observed). In a black- box explanation, Bunge maintains, the 'mechanism' linking input and output is a purely syntactical link between a column of values for the input, I, and a column of values for the output, 0.

In sociology, the most systematized form of black-box explanation can be found in the so-called causal modeling approach (see Duncan 1975), which will be discussed more fully in the next section. In the causal-modeling tradition, the explanatory 'mechanism' simply is a regression coefficient linking I and 0, and this regression coefficient (if the model includes all relevant variables) is supposed to describe the causal influence of I upon 0.

One important difference between black-box explanations and the type of explanation advocated here concerns the information content of the proposed mechanism. Since the alleged 'mechanism' in a black-box explanation (e.g. a regression coefficient) exclusively is derived from I and 0, it contains no information that is not already contained in the events or variables themselves. The approach advocated here does not rest with describing the form of the relationship between the entities of interest but addresses a further and deeper problem: how, i.e. through what process, was the relationship actually brought about?16

Consider the example of poisoning (Bunge 1967). It would be possible to estimate the parameters of an equation describing the relationship between the intake of, say, strychnine and the risk of dying. If the model had the correct functional form, we might even have established a 'covering law' of the dose-response relationship which could be used in subsequent explanations of other occurrences of strychnine intake. But as long as we have not specified the mechanisms that link strychnine intake to morbidity and mortality, the explanation is clearly wanting. By pointing to how strychnine inhibits the respiratory centers of the brain and to the biochemical processes responsible for this paralysis, we provide a mechanism that allows us not only to describe what is likely to happen, but also to explain why it is likely to happen.

A comparison of behaviorist and rational-choice accounts of individual behavior illustrates the same basic point. Explanations in the behaviorist tradition, such as that represented in sociology by the work of George Homans, resemble what we have referred to above as black-box explanations; their aim is to arrive at general propositions relating stimuli to response without invoking any (unobserved) generative mechanism that might have brought about the relationship. Homans's so-called 'success proposition' is a represen- tative case in point: 'For all actions taken by persons, the more often a


particular action of a person is rewarded, the more likely the person is to perform the action' (Homans 1974:16). Rational-choice theory does not rest with observing and describing the form ofthe relationship between reward and behavior, but tries to explain precisely those associations which a behaviorist like Homans is content with only establishing. The rational-choice explanation postulates the existence of a more supple generative mechanism built upon hypothetical constructs such as preferences and intentions (see Hedstr6m, forthcoming). By spelling out a detailed mechanism linking individual behavior and rewards, the rational-choice theory provides a deeper and more fine-grained explanation than behaviorist theory.

One line of sociological research that illustrates the shortcomings of black- box explanations is research on class and its individual correlates. In empirically oriented sociology, individuals' class-belonging has become a popular explanation for various individual-level phenomena such as income (e.g. Kalleberg & Berg 1987) and health (e.g. Townsend & Davidson 1982). The concept of class might be useful for descriptive purposes where it serves as a shorthand for various aspects of individuals' socio-economic living conditions, and research in these traditions has produced informative empirical research describing the living conditions of different 'classes'. Whether the empirical exercise of relating variables describing class and income or class and health also has an explanatory value - in the deeper sense of saying something about why we observe what we observe - is much more doubtful.

Despite the common sociological rhetoric of describing class as a 'determinant' of various individual traits and behaviors, class in and of itself obviously cannot influence an individual's income or health. A 'class' cannot be a causal agent because it is nothing but a constructed aggregation of occupational titles. A statistical association between 'class' and income, or 'class' and health, tells us that individuals from certain 'classes' have lower incomes or worse health than others, but it says nothing about why this is the case. To answer such questions it is necessary to introduce and explicate the generative mechanisms that might have produced the observed differences in average income or health between the occupational groups that the researchers have assigned to different 'classes'. A statistical 'effect' of a class-variable in contexts like these is essentially an indicator of our inability properly to specify the underlying explanatory mechanisms. The worse we do in specifying and incorporating the actual generative mechanisms into the statistical model, the stronger the 'effect' of the class- variable will appear to be.

It is important to note that both the biochemical mechanism and the rational-choice mechanism referred to above are mechanisms of some generality, and it is this generality that gives them their explanatory power. Simply making up an ad hoc story tailored to a specific case does not constitute an acceptable sociological explanation. Even moderately talented journalists are able to make up these sorts of ad hoc stories, and, as Arthur Stinchcombe once noted, 'a student [of sociology] who has difficulty thinking of at least three sensible explanations for any correlation that he is really interested in should probably choose another profession' (Stinchcombe 1968:13). Serious, non-commonsensical, sociological explanations require mechanisms of some generality.


Generative explanations usually invoke some form of 'causal agent' (Bhaskar 1978) or 'causal power' (Harre 1970), which is assumed to have generated the relationship between the entities being analyzed. It is by explicitly referring to these causal agents that the relationship is made intelligible. In the natural sciences, causal agents come in a variety of forms such as organic reactions in chemistry and natural selection in biology. In sociology, however, the elementary 'causal agents' are always individual actors, and intelligible social mechanisms should, in our opinion, always include explicit references to the causes and consequences of their actions.17 This principle of methodological individualism is motivated by the same core idea as is advocated throughout this article: understanding is obtained or enhanced by making explicit the underlying generative mechanisms that link one state or event to another, and in the social sciences actions constitute this link.

It is important to note that explanatory mechanisms, in the natural as well as in the social sciences, often are unobserved or only observable in their effects. Weinberg (1993) emphasizes the important role that unobserved entities have played in physics. For example, the existence of both the electron and the neutrino was conjectured and their roles in various physical processes were usefully theorized, long before they actually were observed. Similarly, the social sciences routinely postulate the existence of unobserved explanatory mechanisms. Assumptions of intentions, discounting, and preferences have proven extremely useful for the analysis of individual action even though they never can be observed. Mechanisms thus are theoretical constructs that provide hypothetical links between observable events. In many situations the operation of a postulated mechanism can only be tested by logically deriving the effects that should be observed if the mechanism was operating as assumed in the theory, and then comparing these theoretical expectations with what actually is being observed.

Elster (1989) appears to have a slightly different view of the role of unobserved mechanisms in scientific explanations. He argues that mechanisms should provide an account of what happened as it actually happened, and not as it might have happened. No one would dispute the correctness of this proposition if it were possible to realize, but accounting for something 'as it actually happens' is always problematic. As argued by Bunge (1967), simply describing all the events, microscopic and macroscopic, that take place in a room during one second would - if it were technically possible - take centuries. Thus, when describing 'what happened', we can never cite all events immediately preceding the event to be explained (not to mention more distant events), but we must be highly selective in what events we chose to include in our description of what 'actually happened' (see also Weber 1949). Hence, mechanisms as well as general theories can refer only to a -subset of the potentially important events, and they can therefore only give plausible accounts of what happened as it could have happened.18

The belief in explanations that provide accounts of what happens as it actually happens has pervaded the sociological literature for decades and has produced an abundance of detailed descriptive narratives, but few explanatory mechanisms of any generality. It is through abstractions and analytical accentuation, however, that general mechanisms are made visible. But these


*. *. . ......

. . ;

abstractions also distort by their nature the descriptive account of what actually happened, by accentuating certain aspects of the situation and ignoring others. Francis Crick's characterization of the process through which good biological theories are arrived at is, in our opinion, equally valid for the social sciences: 'To produce a really good biological theory one must try to see through the clutter produced by evolution to the basic mechanisms lying beneath them' (Crick 1989:138; see also Van Parijs 1981). And as Rom Harre has argued, making hypothetical models of unknown mechanisms is usually what moves a scientific field forward:

Generally speaking, making models for unknown mechanisms is the creative process in science, by which potential advances are initiated, while the making of models of known things and processes has, generally speaking, a more heuristic value. (Harre 1970:40)

6. Variables versus social mechanisms The widespread use and knowledge of survey analysis and the statistical techniques needed for analyzing such data have clearly improved the ability of sociologists to describe social conditions and to test sociological theories. But the increasing use of these techniques has also fostered the development of a variable-centered type of theorizing that pays only scant attention to explanatory mechanisms. Coleman (1986) has aptly described this type of sociology as a form of 'individualistic behaviorism'. The guiding principle behind this type of theorizing - usually referred to as 'causal-modeling' - is the notion that individual behavior can and should be explained by various individual and environmental 'determinants', and the purpose of the analysis is to estimate the causal influence of the various variables representing these determinants.19

According to Coleman, this emphasis on 'causal' explanations of behavior represented a considerable change from the type of explanatory account used in the earlier tradition of community studies: 'One way of describing this change is to say that statistical association between variables has largely replaced meaningful connection between events as the basic tool of description and analysis' (Coleman 1986:1327-1328). In the causal-modeling tradition, variables and not actors do the acting (Abbott 1992).2o

The tension between a variable-centered causal approach to sociological theorizing and a generative view emphasizing the importance of social mechanisms came to the fore in an exchange between Robert Hauser and Raymond Boudon in the mid-1970s. The context of this exchange was a review by Hauser of Boudon's (1974) book on education and inequality. In this book Boudon developed a theoretical model which he hoped would make intelligible a number of apparent paradoxes reported by empirical research on social mobility.21 Hauser suggested numerous changes to Boudon's model, but the main message of his article was a strong disbelief in the very idea that had motivated Boudon to write the book, i.e., that an important distinction should be made between statistical and theoretical models, and that theoretical models are needed to explain the results of an empirical analysis:


Boudon dismisses several standard representations of the mobility process as being 'basically statistical'. I can only guess what this means - perhaps that they are rich in formal properties or that sampling distributions of their parameters are known. Neither of these properties strikes me as undesirable, and these models do have coherent and intuitively meaningful interpretations relative to the mobility process. (Hauser 1976:923)

Boudon responded by noting that descriptive models of the sort advocated by Hauser are undoubtedly useful for many purposes, but that their usefulness for causal analysis is considerably more restricted than assumed by Hauser. According to Boudon, understanding normally is achieved not by the means of descriptive models such as path-models, but through theoretical models which show the logic of the process being analyzed. In order to understand this logic, Boudon argued 'we must go beyond the statistical relationships to explore the generative mechanism responsible for them' (Boudon 1976:117).

One way of describing the difference between Boudon and Hauser is through the distinction between descriptive and structural models. Hauser, being one of the leading figures in the causal-modeling tradition, had a strong commitment to the idea that it is possible to estimate true structural models on the basis of non-experimental data, i.e., models expressing invariant causal relationships between different sociological and demo- graphic variables. Boudon, on the other hand, viewed regression models as purely descriptive and therefore in need of explanation. As Boudon expressed it in a different context,

causal analysis does not explain the [statistical] chart. It simply summarizes it. Understanding a statistical structure means in many cases building a generating theory or model . . . that includes the observed empirical structure as one of its consequences. (Boudon 1979:51-52)

The position taken by Hauser and others in the causal modeling tradition has also been challenged by sociologists such as Mark Granovetter, who has argued that these sorts of correlational analyses can be useful in ruling out theories and arguments previously taken seriously, but that they are wanting because they cannot tell 'by which mechanisms these correlations have their effects, or what broader historical and socio-economic forces have set these mechanisms in motion' (Granovetter 1982:259-260).

The statistician David Freedman (1991, 1992a, 1992b) has discussed the statistical foundations of the causal modeling approach in some detail. According to Freedman, the belief of some social scientists in the possibility of estimating true structural models is both naive and counterproductive. The basic tools of causal modelers such as path analysis and its latent variable counterparts, Freedman argues, are based upon a network of highly restrictive stochastic assumptions that rarely, if ever, are fulfilled. The basic thrust of Freedman's argument is that social scientists need to think more about underlying social processes, and they also need to look more closely at data without the distorting lens of conventional and, according to Freedman, largely irrelevant stochastic models: 'In my opinion, the confusion between descriptive and structural models pervades the social-science scholarly literature of the past 20 years, and has distorted the research agenda of a generation' (Freedman 1992b: 123). According to Freedman, investing even


more time and intellectual energy in trying to estimate non-existing parameters would not be a particularly worthwhile activity. At best, these types of statistical models can provide compact descriptive summaries of the data - but they cannot in themselves provide causal explanations.22

The epidemiological research tradition has produced some important and duly celebrated examples of non-experimental empirical research leading to the identification of genuine causal mechanisms. Snow's research which suggested that cholera was a water-borne disease, and Doll's research on the relationship between smoking and lung cancer are perhaps the most notable examples (see Doll & Peto 1981; Hamlin 1990). But these success stories appear to be the exceptions that probe the rule (and Freedman no doubt would attribute part of their success to the fact that they did not use structural equation models). Despite some 30 years of causal modeling carried out by some of the most gifted sociologists of this generation, no similar findings have been reported in the sociological literature. Given this paucity of results, it might be time for causal modelers to contemplate the implications of David Freedman's (1992b) advice that causal inferences should always ride on the strength of the argument, and not on 'the magic of least squares'.23

So where does this leave us? We do not wish to suggest that quantitative empirical research is of minor importance for the sociological enterprise. Quite the contrary: Quantitative research is essential both for descriptive purposes and for testing sociological theories. We do, however, believe that many sociologists have had all too much faith in statistical analysis as a tool for generating theories, and that the belief in an isomorphism between statistical and theoretical models, which appears to be an integral feature of the causal modeling approach, has hampered the development of sociological theories built upon concrete explanatory mechanisms.

Over the past few years, one can discern a movement away from the 'hard core' position represented by Hauser. Nevertheless, the way in which quantitative sociologists still allocate their time and intellectual energy between statistical and theoretical modeling reveals a strong preference for description and testing of hypotheses formulated by others. 4 As suggested by Stinchcombe (1993:27-28), sociologists in the multivariate modeling tradition still 'make only rhetorical use of the language of mechanisms' and they rarely show any serious intellectual commitment to developing the theoretical foundation of the discipline themselves.

7. Social mechanisms: some selected examples In order to concretize the idea of general social mechanisms underlying a range of different social processes, we briefly examine three well-known theories in sociology - the self-fulfilling prophecy (Robert Merton), network diffusion (James Coleman), and threshold-based behavior (Mark Granovet- ter) - and we suggest that all are founded upon the same basic belief- formation mechanism.

The self-fulfilling prophecy is perhaps the most famous of all mechanisms-based theories in sociology and was formulated in 1948 by Robert Merton in a seminal article (Merton [1948] 1968). The basic idea is that an


initially false definition of a situation evokes behavior that eventually makes the false conception come true. The key example that Merton uses to illustrate his argument is a run on a bank. If a rumor of insolvency somehow gets started, some depositors will withdraw their savings. Their withdrawal will strengthen the belief in the rumor, partly because the withdrawals actually may hurt the financial standing of the bank, but more importantly because the act of withdrawal in itself signals to others that something indeed might be wrong with the bank. This produces even more withdrawals, which further reduces the trust in the bank, and so on. Because of the operation of this mechanism, even an initially sound bank may go bankrupt if enough depositors withdraw their money in the (initially) false belief that the bank is insolvent.

The study of network diffusion processes is an important area of sociological research (cf. Burt 1987; Marsden & Podolny 1990; Strang & Tuma 1993; Hedstrom 1994b). To a considerable extent this research is inspired by Coleman, Katz & Menzel's classic study of the diffusion of a new drug (see Coleman, Katz & Menzel 1957, 1966). Their main finding was that the physicians' positions in various professional networks influenced the diffusion process, particularly during the period immediately after the new drug had been introduced on the market. Their explanation for this finding is reminiscent of Merton's argument about the self-fulfilling prophecy:

Why should these sociometric ties to colleagues who have used the drug be influential during the first months of the drug's availability, but not later? One possible answer lies in the greater uncertainty about the drug that must have prevailed when it was new . . . We know from work in the tradition of Sherif that it is precisely in situations which are objectively unclear that social validation of judgments becomes most important. More generally, this explanation implies that a doctor will be influenced more by what his colleagues say and do in uncertain situations, whenever and wherever they may occur, than in clear-cut situations. (Coleman, Katz & Menzel 1957: 268-269)

The core of their argument is consequently that networks are important because information about innovations, in this case a new drug, diffuse through them, and that an individual's propensity to adopt the innovation is influenced by what others do, particularly when there is a great deal of uncertainty about the true value of the innovation.

Our final example is Granovetter's threshold theory of collective behavior (see Granovetter 1978; Granovetter & Soong 1983). Granovetter argued that an individual's decision whether or not to participate in collective behavior often depends in part on how many other actors already have decided to participate. He further argued that actors differ in terms of the number of other actors who already must participate before they decide to do the same, and he introduced the concept of an individual's 'threshold' to describe this individual heterogeneity. An actor's threshold denotes the proportion of the group which must have joined before the actor in question is willing to do so.

An important qualitative result of Granovetter's analysis was that even slight differences in thresholds can produce vastly different collective


outcomes. Assume, for example, a group of 100 people. One individual has a threshold of 0, another has a threshold of 1, a third has a threshold of 2, and so on up to the last individual who has a threshold of 99. Initially only the person with a threshold of 0 will participate. His/her participation will activate the person with a threshold of 1 and this person's participation, in turn, will activate the person with a threshold of 2. This process will continue until all 100 people participate. If the distribution of thresholds changed slightly - for example if the person with a threshold of 1 was replaced with a person with a threshold of 2 - the collective outcome would change dramatically. The initiator, of course, will participate also under these new conditions. But since there is no one with a threshold of 1, the process ends at this point; only one person will participate in the 'collective' movement. The populations are virtually identical, but the collective outcomes are vastly different (see Granovetter 1978).

Granovetter gives a range of examples of threshold-based behavior, but the following example illustrates particularly well the logic behind this sort of conditional behavior:

Suppose you are in an unfamiliar town and enter an unknown restaurant on Saturday evening at seven o'clock. W)hether or not you decide to take a meal there will depend in part on how many others have also decided to do so. If the place is nearly empty, it is probably a bad sign - without some minimal number of diners, one would probably try another place. (1978:1438-1439)

The reason that the number of visitors at the restaurant is likely to influence an individual's choice of restaurant (or more generally, why the number of participants in a collective action is likely to influence an individual's decision whether or not to join the action), Granovetter argues, is that in situations of uncertainty, the number of diners (movement participants) is a signal about the likely value of the action (e.g. the quality of the food being served or the benefits that are likely to accrue to the individual if he/she joins a particular group for collective action), and this signal may be decisive for the individual's choice of action.

In order more clearly to see the logical structure of the arguments advanced by Merton, Coleman, and Granovetter it is useful to adopt a slightly more formalized language. Let

Pit = propensity of individual i to perform the act being analyzed at time t, e.g. withdrawing savings from the bank, adopting a new drug, visiting a restaurant, or joining an organization for collective action, and bit = the strength of individual i's belief in the value or necessity of performing the act in question at time t.

All three authors assume that individuals are goal directed and that an individual's propensity to perform the act being analyzed is an increasing function f of the individual's belief in the value of performing the act: Pit = f(bit). However, the core mechanism that gives Merton's, Coleman's, and Granovetter's analyses their counter-intuitive appeal concerns the ways in which individual beliefs are being formed. More specifically, their proposed mechanism states that individual i's belief in the value or necessity of performing the act is a function of the number of other individuals who


performed the act at time t-1. Merton's bank customers based their judgments about the solvency of the bank on the number of other customer withdrawing their savings from the bank; Coleman's physicians based their evaluations of the possible effect of the new drug on the doings of their colleagues; and Granovetter's restaurant visitor based his/her decision on the number of diners already in the restaurant. That is, they all assumed that

bit= g(nt--l)

where

nti, = number of individuals performing the act time t-1, and g is an increasing function.

Inserting this expression into the former one, we arrive at Pit = f(g(nt-1)) which suggests that an individual's propensity to withdraw savings from the bank, adopt a new drug, visit a restaurant, or join an organization for collective action is an increasing function of the number of other individuals who already have performed the same act.

The main difference between the three theories considered here centers on the function g, which provides the fine-grained details of the link between bit and nt1l, and the details of this link will influence the aggregate dynamics of the system.25 But the core characteristic of these theories that gives them their non-obvious character and appeal is the general belief-formation mechanism which states that the number of individuals who perform a certain act signal to others the likely value or necessity of the act, and this signal will influence other individuals' choice of action. It is this belief- formation mechanism that is at the heart of the self-fulfilling prophecies of Merton, the network effects of Coleman, and the bandwagon effects of Granovetter.26 On the fundamental level of mechanisms, the run on the bank, the prescription of the drug, and the emergence of the collective movement, all are analagous.27

8. Social mechanisms: a typology In order to specify in more general terms the types of mechanisms we believe to be of particular importance for sociological theory, we propose a tentative typology. This typology takes its departure from James Coleman's well known model for how to conceptualize social action, the so-called macro- micro-macro model (see Figure 1).

The general thrust of this model is that proper explanations of macro- level change and variation entail showing how macro-states at one point in time influence the behavior of individual actors, and how these actions add up to new macro-states at a later time.28 That is, instead of analyzing relationships between phenomena on the macro level, one should always try to establish how macro-level events or conditions affect the individual (Step 1), how the individual assimilates the impact of these macro-level events (Step 2), and how a number of individuals, by their actions and interactions, generate macro-level outcomes (Step 3). This way of conceptualizing social


Macro level

(1) \ (3)

Micro level

(2)

Figure 1. Macro-micro-macro relations, according to James Coleman. Source: James S. Coleman, 'Social Theory, Social Research, and a Theory of Action', American Journal of Sociology, May 1986, pp. 1309-1335.

action lends itself in a very natural way to a typology of mechanisms: macro- micro mechanisms, micro-micro mechanisms, and micro-macro mechanisms - and a few words will be said about each of these.29

The first of these three types of mechanisms covers the macro-to-micro transition, and following the suggestion of Stinchcombe (1993) we refer to it as a situational mechanism. Erving Goffman's (1963) work on behavior in public places and Karl Popper's form of situational analysis (cf. Popper 1994) have these sorts of mechanisms at their core. The belief-formation mechanism discussed above, opportunity-generating mechanisms such as White's (1970) vacancy chains, and preference-formation mechanisms such as those expressed in the idea of reference groups (see Merton & Rossi 1968; Boudon 1988), are prototypical examples of general social mechanisms that in a systematic and reasonably precise way link a social structure or other macro-sociological state to the beliefs, desires, and opportunities of individual actors.

The second type of mechanism is a micro-level mechanism, and we refer to it as an individual action mechanism. This type of mechanism shows how a specific combination of individual desires, beliefs, and action opportunities generates a specific action. A plurality of psychological and social psychological mechanisms operates at this level. General decision theories as well as more specific theories such as Leon Festinger's (1957) theory of cognitive dissonance and George Ainslie's (1992) on discounting illustrate different types of action mechanisms. One concrete example that Coleman uses to illustrate individual action mechanisms comes from his reading of The Protestant Ethic (see Figure 2). The micro-to-micro transition has in this case to do with the individual believer's realization that his or her values also imply a change in orientation towards economic activities, followed by action inspired by these values.30

The third type of mechanism covers the micro-to-macro transition, and we propose to call it a transformational mechanism. Here a number of individuals interact with one another and the specific mechanism (which


Macro: Protestant Capitalist religious economic doctrine system

Micro: -_ _ _ _

Individual Orientations to values economic behaviour

Figure 2. Weber's Protestant Ethic, conceptualized according to Coleman's model. Source: James S. Coleman, 'Social Theory, Social Research, and a Theory of Action', American Journal of Sociology, May 1986, p. 1322.

depends upon the type of interaction) describes how these individual actions are transformed into a collective outcome, sometimes unintended and unexpected by all actors. Several of the theories mentioned elsewhere in this paper - such as Schelling's tipping model, standard game-theoretic models such as the tragedy of the commons, and neoclassical market models - are built upon and illustrate specific transformational mechanisms.

9. Concluding remarks In this concluding section we briefly summarize the main thrust of our argument (see also Hedstrom & Swedberg, forthcoming (b)). We have argued that the notion of social mechanisms is essential for sociological theory, and that mechanism-based explanations are characterized by three core features:

1. The principle of direct causality; 2. The principle of limited scope; 3. The principle of methodological individualism.

The first of these principles - direct causality - has essentially to do with opening up the black-box, and that one should always strive to narrow the gap or lag between input and output, cause and effect. A mechanism-based explanation seeks to provide a fine-grained and tight coupling between explanans and explanandum.

The second principle - limited scope - captures the essence of middle- range sociology and expresses the idea that sociology should not prematurely try to establish universal social laws (which are unlikely to even exist) - but


should instead aim at explanations specifically tailored for a limited range of phenomena.

The third principle - methodological individualism - captures the idea that in the social sciences, actors and not variables do the acting. A mechanism-based explanation is not built upon mere associations between variables, but always refers directly to causes and consequences of individual action oriented to the behavior of others. A corollary to this principle states that there exist no macro-level mechanisms; macro-level entities or events are linked to one another via combinations of situational, individual action, and transformational mechanisms, i.e., all macro-level change should be conceptualized in terms of three separate transitions (macro-micro, micro- micro, and micro-macro).3'

A general social mechanisms can now be defined in the following way: a social mechanism is an integral part of an explanation which (1) adheres to the three core principles stated above, and (2) is such that on the occurrence of the cause or input, I, it generates the effect or outcome, 0.

We realize that this definition may seem excessively general and abstract. But it is not so much the definition per se that is important, as the type and style of theorizing it encourages. We believe that there is a natural and important affinity between Robert Merton's idea of middle-range theory and the idea of social mechanisms, in the sense that social mechanisms are the elementary building blocks of such theories. Other types of sociological theory tend to make only rhetorical use of the notion of social mechanism; and this goes for grand theory (which often ignores all three principles stated above) as well as for variable sociology (which ignores the principle of individual action). A focus on explanatory mechanisms helps sociology to avoid the trap of mindless empiricism on the one hand, and conventional and empty theorizing on the other.

First version received October 1995 Final version accepted April 1996

Acknowledgements We thank Mario Bunge, Cecilia Gil-Swedberg, Mark Granovetter, Barbara Hobson, Ole-J0rgen Skog, Arthur Stinchcombe, Michael Tahlin, Lars Udehn, seminar participants at the Department of Sociology, Stockholm University, participants at the conference on Social Mechanisms held at the Royal Swedish Academy of Sciences, June 6-7, 1996, and two anonymous referees for their useful comments on an earlier version of this article. We owe special thanks to Carl-Gunnar Janson for his detailed written comments, and to Alejandro Gil-Villegas and Aage S0rensen for providing valuable background information.

Notes 1 The term 'mechanism' is often used in sociology but in a casual

manner and hence constitutes what Merton calls a 'proto-concept'. Merton explains: 'A proto-concept is an early, rudimentary, particu-


larized, and largely unexplicated idea (which is put to occasional use in empirical research and, indeed, often derives from it); a concept is a general idea which once having been defined, tagged, substantially generalized, and explicated can effectively guide inquiry into seemingly diverse phenomena' (Merton 1984:267).

2 Weber, for example, rarely used the term 'mechanism' (Mechanismus) with the exception of his analysis of bureaucracy, where it is more or less synonymous with 'machine' (see, e.g., Weber [1921-1922] 1978:961, 967, 988; Weber as cited in Marianne Weber 1975:416-417). In Zwischenbetrachtung, Weber makes the following statement, which sums up the situation brought about by Descartes and Newton: 'The tension between religion and intellectual knowledge definitely comes to the fore wherever rational, empirical knowledge has consistently worked through to the disenchantment of the world and its transformation into a causal mechanism (kausalen Mechanismus)' (Weber 1946:350; emphasis added).

3 Simmel's work is rich - and still relatively unexplored - in suggestions on this score. A well-known example is his analysis of the ways in which the number of actors influences the structure of interaction. Durkheim had a powerful sense for social mechanisms that unites the individual and the group, as his various hypotheses in Suicide make clear. Some of Durkheim's analyses of mechanisms are, however, marred by his functionalism, such as the argument that society has a tendency to maintain itself in the face of attacks or threats of dissolution. As for Weber, the work that is usually cited apropos mechanisms is The Protestant Ethic with its argument that the religious idea of vocation (Beruf) came to influence economic behavior in a methodical, capitalist direction. A number of interesting mechanisms can also be found in Weber's later work, especially in Economy and Society and The Economic Ethics of the World Religions.

4 Merton's work on middle-range theory goes back to his critique of Parsons at the 1947 meeting of the American Sociological Association (see Merton 1948). Also Parsons discussed the concept of mechanism, especially in his work from the early 1950s (see, e.g., Parsons 1951:201-325; Parsons & Shils 1951:125-149). Parsons' view, however, was marred by his functionalism as well as by his attempts at grand theory; and the function of social mechanisms was basically reduced to that of maintaining the social system when this was threatened in some manner. One of the first sociologists to show more than a casual interest in the concept of mechanisms is George Lundberg in Foundations of Sociology from 1939. Lundberg argued for a common sense approach to the notion of mechanism, often with functionalist overtones. (We thank Lars Ud6hn for the reference to Lundberg's work.)

5 To this can be added a few other more general mechanisms that were to emerge from Merton's own work as well as from Columbia Sociology in general: the two-step model of communication, the self-fulfilling prophecy, the Matthew Effect, and the diffusion mechanism of Medical Innovation (1966).

6 Though Merton should be praised for discussing 'social mechanisms' in his essay on middle-range theory, it is also true that Merton did not succeed in singling out this concept as much as


one would have wished. See in this context also Social Mechanisms: Studies in Sociological Theory (1958) by the Swede Georg Karlsson. Karlsson's main source of inspiration was Nicolas Rashevsky, whose work he had come into contact with in Chicago and who Lazarsfeld had introduced at Columbia. Karlsson explicitly rejects systems- oriented sociological theory and opts for middle range sociology (Karlsson 1958:10, 16). His work is centered around three families of mechanisms: 'social diffusion', 'group choice mechanisms', and 'general mechanisms of interaction'. When Karlsson returned to Sweden, he soon changed orientation since the intellectual climate in Swedish sociology was hostile to this type of theorizing (interview with Karlsson on 19 September 1995).

7 Of Elster's publications so far, the place where one can find the most complete statement on this topic is in the introduction to Nuts and Bolts for the Social Sciences, entitled 'Social Mechanisms' (Elster 1989:3-10). The clearest statement of Stinchcombe's views on these matters can be found is an article from 1991 (republished in more or less identical form in 1993). See also e.g. Sayer (1984), Pawson (1989), and Kiser & Hechter (1991) for some recent discussions of the role of mechanisms in the social sciences.

8 Tocqueville is a true master of mechanisms, according to Elster (1993), who cites a number of examples from Democracy in America and Ancien Re'gime.

9 For a furious attack on Nuts and Bolts for precisely this reason, see Humphreys (1991).

10 Goffman writes in Behavior in Public Places: 'By the term situation I shall refer to the spatial environment anywhere within which an entering person becomes a member of the gathering that is (or does then become) present. Situations begin when mutual monitoring occurs, and lapse when the second-last person has left' (Goffman 1963:18).

11 The word 'mechanism' originally comes from the word 'machine' (cf. e.g. Oxford English Dictionary 1989). That the association to 'machines' and 'mechanics' is still popular among those who write on social mechanisms is clear from the title of Elster's book: Nuts and Bolts of the Social Sciences.

12 A famous example of a 19th century mechanism is that of homeostasis, discovered by Claude Bernard and usually defined as a self-regulating process through which a biological system maintains its stability. Sociologists will recall that the term 'homeostatsis' was coined by W. B. Cannon, whose work The Wisdom of the Body (1932) deeply influenced Parsons. (In chemistry the same idea is known as the principle of Le Chatelier.) Parsons may also have picked up the idea from Cannon.

13 The problem that Hirschman addresses has to do with what happens when an organization (including a firm) begins to decline. According to Hirschman, two 'mechanisms of recuperation' are usually triggered off in this situation, one that is discussed primarily in economics ('exit') and one that primarily political scientists focus on ('voice').

14 Hempel (1942) uses the example of an automobile radiator cracking during a cold night to illustrate the logic of his proposal. The general laws cited in the explanation would need to refer to how


the pressure of water changes with changes in temperature and volume, and the specific circumstances referred to would be conditions such as the temperature during the night and the bursting pressure of the radiator. A proper explanation has been proposed if, and only if, the proposition about cracking of the radiator can be logically deduced from the sentences stating the laws and the specific circumstances.

15 Mark Granovetter, who is a student of Hempel, disagrees with our argument here and notes that 'If [only] correlations were produced he [that is, Hempel] would no doubt point out that more detailed covering laws are needed to explain the correlations' (personal communication).

16 It should be emphasized that the distinction between 'black- boxes' and 'mechanisms' to some extent is time-bound. In the words of Patrick Suppes (1970:91): 'From the standpoint of either scientific investigation or philosophical analysis it can fairly be said that one man's mechanism is another man's black box. I mean by this that the mechanisms postulated and used by one generation are mechanisms that are to be explained and understood themselves in terms of more primitive mechanisms by the next generation.'

17 For the sake of clarity, it should be noted that we also include 'intentions' among the possible 'causes' of individual action.

18 In this respect, our position is closer to that of Stinchcombe who explicitly argues against those who do not accept that one often has to make simplifying assumptions about the units on the lower level (e.g. homo economicus) in order to be able to generate interesting results on the higher level. In other words, a mechanism does not necessarily have 'to be true to be useful' - but it has to 'produce interesting hypotheses or explanations at the higher level' (Stinchcombe 1993:27).

19 The affinity between behaviorism and structural equation modeling was also noted by 0. D. Duncan himself: 'In [structural equation] models that purport to explain the behavior of individual persons, the coefficients [of the structural equation] could well take the form of units of response per unit of stimulus strength; the structural equation is, in effect, a stimulus-response law' (Duncan 1975:162-163).

20 Throughout his career, Coleman was a strong proponent of a generative view of causality and he often expressed serious doubts about the usefulness of the type of causal analysis referred to above. Already in Introduction to Mathematical Sociology he wrote: 'Note, however, that there is nowhere the proposal simply to engage in curve-fitting, without an underlying model which expresses a social process. If the data happen to fit a simple curve, this may provide an economical statement of the data, in terms of the one or two parameters of the distribution curve. But if there is no underlying model with a reasonable substantive interpretation, little has been gained by such curve fitting' (Coleman 1964:518).

21 As these terms are being used here, a 'theoretical model' differs from a 'mechanism' in primarily two ways: (1) a theoretical model is always formalized, something which mechanisms only sometimes are, and (2) a mechanism is a more elementary entity


than a theoretical model; (formalized) mechanisms often constitute the building-blocks of models.

22 Another important reason for why the causal modeling tradition has had such moderate success in sociology is the character of the data being used. The inductive approach adopted in this tradition is modeled upon experimental research, but the data being used are normally of a non-experimental kind. As emphasized by Lieberson (1985), unmeasured selection is a serious obstacle to causal inferences when using non-experimental data.

23 As exemplified in the work of John Goldthorpe (forthcoming), there is an emerging consensus being established even among empirically oriented sociologists that causality in social processes cannot be established from quantitative analyses alone.

24 In areas such as labor market sociology, the hypotheses being tested have furthermore usually been formulated by members of other scientific disciplines, i.e., by economists. There are numerous empirical tests being reported in the sociological literature of human capital, internal labor markets, dual labor markets, and transaction costs, all theories or hypotheses developed by economists, but exceptionally few tests of mechanisms proposed by sociologists; White's (1970) vacancy chain mechanism being one noteworthy exce tion.

V Coleman assumed that g was a function of the sociometric ties, Granovetter assumed that it was a function of individual thresholds, and Merton left the functional form unspecified. When mechanisms are expressed in mathematical language they appear as functions transforming variables. These functions can be distinguished from one another on the basis of their functional form and their6parameter values (see Hernes 1976).

2 A process like this might also arise in a situation where not all actors form their beliefs on the basis of the mechanisms discussed above. Consider the following situation: (1) I do not believe in proposition A; (2) I know (or believe) that many others believe in A and their belief in A will have negative consequences for me; (3) other's belief in A will induce me to act as if A were true; and this (4) will signal to others the correctness of proposition A. We believe that recent instability on various financial markets can partly be attributed to these types of processes. But also social processes, such as the fear of magnetic fields referred to earlier, exhibit these characteristics. If this fear threatens to undermine the property values of houses close to power lines, houseowners (even those who have realized that the fear is groundless) are induced to put their houses on the market, and this 'escape' sends a signal to others that there indeed must be some substance to the view that living close to a power line is a potential health hazard. This threatens to further reduce property values, and so on.

27 In addition to this belief-formation mechanism, there are of course other action and transformation mechanisms that are involved in Merton's, Coleman's, and Granovetter's analyses, but these mechanisms are commonplace and tangential to the core processes they analyze.

28 It is important to note that this form of methodological individualism does not imply that macro-level factors are unim-


portant or somehow theoretically inappropriate when it comes to explaining individual action. It only implies that these extra- individual entities also in principle should be accounted for with reference to the intended and unintended consequences of individuals' past behavior (see Hedstrom & Swedberg, forthcoming (a)).

29 The logic of Coleman's argument also suggests that any kind of continuous social action can be conceptualized as a long chain of successive macro-micro-macro transformations, where, in many cases, only the peaks, so-to-speak, ('macro-macro') are visible to the researcher - but where the analytical point is precisely to explain this cumulative social action as a result of a large number of macro- micro-macro transitions.

30 Coleman's interpretation of Weber in this example has been challenged by several authors, but this does not affect the logic of Coleman's argument (see Swedberg, forthcoming).

31 In addition to these basic characteristics of social mechanisms, the ideal mechanism, it seems to us, should also be simple and non-obvious.

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1996 Hedstrom Swedberg Social Mechanisms

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