MPIfG Working Paper
03/3, April 2003
in the Analysis of Macro-Social Phenomena
Max Planck Institute for the Study of Societies
The paper is a contribution to a forthcoming special
issue of the Journal Philosophy of the Social Sciences, edited by Andreas Pickel. The term (social) mechanism can be found frequently
in recent social science literature, but only few authors have attempted to
spell out systematically what exactly the term refers to. The paper begins by
trying to close this gap. Use of the term (social) mechanism is the hallmark of
an approach that is critical of the emphasis on correlational analysis, and on
the covering-law model of explanation. The term mechanism, it is argued, should
be used to refer to recurrent processes generating a specific kind of outcome or
event; mechanism statements are accordingly statements about recurrent
processes. Explanation of social macro phenomena by mechanisms typically
involves causal regression to lower level elements, as stipulated by
methodological individualism. But while we already have a good-sized
tool-box of mechanism models at hand to explain emergent effects of different forms of
collective behavior, we lack a similarly systematic treatment of generative
mechanisms where structural configurations and corporate actor constellations
play the decisive role in the production of an effect.
Das Papier wird als Aufsatz in einem von Andreas
Pickel herausgegebenen, in Vorbereitung befindlichen Sonderheft der Zeitschrift
Philosophy of the Social Sciences erscheinen. Der Begriff (sozialer) Mechanismus findet sich relativ
häufig in der neueren sozialwissenschaftlichen Literatur, aber nur wenige
Autoren widmen sich einer systematischen Begriffsklärung, wie sie hier
einleitend versucht wird. Mit der Verwendung des Begriffs (sozialer) Mechanismus
ist gewöhnlich eine Kritik am korrelationsanalytischen Ansatz und an
nomologisch-deduktiver Erklärung verbunden, die den Prozesscharakter sozialer
Wirklichkeit ausblenden. Der Begriff Mechanismus, so wird argumentiert, sollte
speziell zur Bezeichnung wiederkehrender Prozesse dienen, die am Zustandekommen
bestimmter Makrophänomene beteiligt sind. Eine Erklärung von Makrophänomenen
durch Mechanismen geschieht gewöhnlich durch kausale Regression auf eine
niedrigere Systemebene. Das entspricht dem Modell des methodologischen
Individualismus, der allerdings durch die Reduktion auf individuelles Handeln
jenen Transformationsmechanismen kaum gerecht wird, bei denen strukturelle
Konfigurationen und Akteurkonstellationen die kausal entscheidende Rolle
Thinking in terms of mechanism has a venerable tradition. It can be traced to
seventeenth century realist philosophy "which brought with it a much closer
attention to the mechanics of scientific experimentation and laid great stress
on how physical laws are explained by the action of underlying, microscopic
mechanisms" (Hedström/Swedberg 1996, 285). In today's social sciences, an
explicit search for and interest in mechanisms is typically advocated by
sociologists and philosophers of science who oppose the dominant tradition of
correlational (or multivariate) analysis in quantitative research. The critique
of correlational analysis has been aptly summarized by Mahoney (2001, 575-577);
correlations, even non-spurious correlations in which the time order is well
established, are inherently limited representations of causal processes.
"[P]ositivists since Hume ... have redefined causation as regular
conjunction or succession", Bunge (1997, 423) states, but the aim is
"to step away from the description of regularities to their
explanation" (Pawson 2000, 288) and to look for the mechanisms underlying
such associations. This argument is made in similar form by most authors who are
critical of the explanatory power of correlational analysis, the
variable-centered type of theorizing.
The general methodological problem of the explanatory potential of
correlational analysis is particularly acute for research dealing empirically
with such macro-phenomena as regime transformation, the welfare state crisis, or
European integration. Where research on such topics aims to go beyond
description and produce general theoretical statements, it is confronted by the
well-known small-N problem. To solve this problem, techniques have been
developed that permit the formulation of general statements on the basis of a
systematic and preferably quantitative comparison of a small number of cases.
Examples are the increasingly popular pooled time-series cross-section analysis
(Beck/Katz 1995), and Ragin's analytical techniques based on Boolean algebra and
fuzzy set theory (Ragin 1987, 2000). These formalizing and quantifying
approaches have been criticized on technical grounds such as the validity of
their operationalizations, but also because they only permit to make statements
about the co-variation of properties, while the nature of the causal
relationship involved remains a black box. To overcome this explanatory deficit,
an approach that has variously been called "systematic process
analysis" (Hall 2003) or "causal reconstruction" (Mayntz 2002) is
being advocated. Causal reconstruction does not look for statistical
relationships among variables, but seeks to explain a given social phenomenon -
a given event, structure, or development - by identifying the processes through
which it is generated. Causal reconstruction may lead to a (more or less
complex) historical narrative, but in its theoretically more ambitious version,
causal reconstruction aims at generalizations - generalizations involving
processes, not correlations. The identification of causal mechanisms is the
hallmark of such an approach.
If mechanisms are crucial in the causal reconstruction of social
macro-phenomena, the concept should be fashioned as a sharp analytical
instrument. But a survey of the relevant empirical and methodological literature
soon bogs down in a mire of loose talk and semantic confusion about what
"mechanisms" are. There are not many social scientists or philosophers
of science who have tried to deal with the topic more systematically. Among
social scientists, the names most frequently mentioned in this connection are
Boudon, Coleman, Elster, Hedström and Swedberg, Merton, and Stinchcombe. Even
among these authors there is no agreement about the defining criteria of
"(social) mechanism". A still incomplete list of definitions assembled
by Mahoney (2001, 579-560) counts 24 different definitions by 21 authors.
Mechanisms are considered to be lawful processes, yet they are also opposed to
laws. The term mechanism is moreover applied to a host of highly diverse
phenomena - from rational choice to the French revolution, from driving forces
(or factors) such as social norms (e.g. Elster 1989, Petersen 1999, 63) to
outcomes of interaction processes such as voluntary agreement (Knight 1995,
105). Part of the semantic noise thus created follows from the ambiguity of many
of our basic social science concepts, concepts that can refer both to a process
and to a (static) outcome. "Cooperation" and "competition"
are but two of many examples. Of course it is entirely legitimate to label a
mechanism that has been spelled out in detail by a noun that refers to a
process, an outcome, or a factor. But to use a terminological label merely to
allude to a process that remains unspecified has no more explanatory value than
the simple statement of a correlation. This article is a plea for a more
disciplined use of the concept of social mechanism. To this purpose, I shall
discuss some of the more confusing issues in the use of the concept, especially
as it is used in the causal reconstruction of social macro-phenomena. The
distant goal of this discussion is an analytical frame to guide explanation in
terms of mechanisms. This goal can of course not be reached in this article, but
hopefully a road leading towards it will have been charted in the end.
2What Mechanisms Are, and What They Are Not
The term "mechanism" is used both to designate a certain class of
real phenomena (mechanisms are such and such, they do such and such), and to
designate a class of (causal) propositions referring to such phenomena.
Statements about social mechanisms are often considered to be the building
blocks of middle-range theories, advocated by Merton (1957) to avoid the vain
search for social laws. Merton's view that mechanisms constitute the middle
ground between description and social laws was quickly taken over by Karlsson
(1958), and has since been reiterated, among others, by Hedström and Swedberg
(1996, 282-284), Elster (1998), Pawson (2000), and Esser (2002). To contrast
mechanisms to social "laws" means to oppose an explanation by
mechanisms to the covering-law model of causal explanation. The covering-law
model is often criticized for the same reason brought against correlational
analysis: A nomological-deductive explanation involving lawlike propositions
"supplies no understanding" (Bunge 1997, 412), it "give(s) no
clue whatsoever as to why" a relationship exists: "Covering-law
explanations in the social sciences therefore normally are 'black-box'
explanations" (Hedström/Swedberg 1996, 287). Unlike correlations, however,
the "laws" used in nomological-deductive explanations are (often
implicitly) taken to be characterized by a high degree of generality, if not
universality. This is a second, and different, issue raised by the covering-law
model: In the social world we do not find anything like the universal laws of
physics. Physical laws presuppose elements that are invariant in time and space,
but in the social world, elements vary substantially in historical time and
cultural space. Instead of vainly looking for "laws" that do not exist
in the social world, we are advised to look for social mechanisms, which are
perceived as regularities of a less general scope than laws. 
argument is, however, only plausible if the terms "law" and
"lawful" refer to propositions of near-universal applicability. But
the logic of a nomological-deductive explanation does not necessarily require
universal and deterministic laws; the law-like proposition "If A, then
B" may explicitly include a ceteris paribus clause that limits its
applicability in time and space. On the other hand, the middle-ground argument
also ignores the fact that statements of mechanisms vary widely in their degree
of generality (or abstraction). The main difference between a mechanism approach
and a covering-law approach is not that mechanism statements are less general
than the propositions in a nomological-deductive explanation, but that in the
analytical theory of science (e.g. Nagel 1961, Hempel 1965), "laws"
are basically general statements about co-variation, i.e. "laws" point
out causal factors, and not processes.
Ontologically speaking, the term mechanism refers to recurrent processes
linking specified initial conditions and a specific outcome. This holds for
mechanisms in general; in the case of social mechanisms, social phenomena are to
be explained. If social mechanisms refer to recurring processes, mechanism
concepts must be "truncated abstract descriptions"
(Machamer/Darden/Craver 2000, 15). Statements of mechanisms are accordingly
generalizing causal propositions. This criterion is, however, not unanimously
accepted. Occasionally the term mechanism is also applied to unique (historical)
causal chains. Boudon even includes this possibility in his definition when he
calls a social mechanism (SM) "the well-articulated set of causes
responsible for a given social phenomenon. With the exception of typical simple
ones, SMs tend to be idiosyncratic and singular" (Boudon 1998, 172).
Helmström and Swedberg (1996, 289) on the other hand require "some
generality" in their definition, and at least implicitly most authors agree
that mechanism statements are causal generalizations about recurrent processes.
In this sense the term shall be used in this article.
Substantively speaking, mechanisms state how, by what intermediate steps, a
certain outcome follows from a set of initial conditions. A mechanism provides a
clear causal chain, it is "concrete, lawful, scrutable" (Bunge 1997,
439). While we may designate or label such processes by a single term, a
mechanism is only identified when the process linking an outcome and specific
initial conditions is spelled out. Causal propositions about mechanisms are
correspondingly complex formulations. It is, for instance, not enough to state
that ideas etc. influence behaviour; interpretive theories require "a
plausible mechanism to account for how symbols, traditions, rituals, and myths
influence social and political interaction" (Johnson 2002, 227; emphasis
added).The specification of causal chains is what distinguishes propositions
about mechanisms from propositions about correlations.
The notions of "causal chain" and "underlying process"
imply that there should not be too much proximity between cause and effect. If a
cause produces an effect without intermediate steps, no mechanism is involved,
and the stated relationship even runs the danger of being a tautology (Kitschelt
2003). The term mechanism should therefore be reserved for processes involving
linked activities of several units or elements, and not applied to "unit
acts". As Elster (1989, 7) puts it, a causal mechanism typically has
"a finite number of links". Most authors seem to share this view, even
if only implicitly, as when they say that a mechanism involves a series of
events linking certain initial conditions with a given effect (e.g. Little 1991,
15). In general discussions of the mechanism concept, the links are conceived of
as "entities" and "activities" - still very much in the
seventeenth century tradition of early mechanistic thought, but applicable also
to social mechanisms. Entities and activities are organized in a process that
leads "from start or set-up to finish or termination conditions"
(Machamer/Darden/Craver 2000, 3). Craver, who uses examples from biology, adds
that mechanisms have an "active organization", which is "...
sustained by their characteristic spatial and temporal organization"
(Craver 2001, 60).
Whereas the spatial organization of the components is of obvious importance
for biological mechanism, its role in social mechanism has never been
systematically discussed. Temporality, on the other hand, is clearly a
characteristic of social mechanisms: social mechanisms are recurrent processes
taking place in time. This, however, does not mean that mechanisms are always
organized in a linear way, causal chains in which one element after the other is
activated, as in a wave rippling through a lake, or a chain reaction involving
each component only once. Mechanisms may consist of a sequence of actions
involving different social elements, as in a diffusion process. But they can
also involve repeated actions of the same elements, as in an escalation process.
The causal chain can contain feedback loops, and each unit involved in the
process may undergo changes (Büthe 2000, 485). The causal structure of
mechanisms can, in other words, be linear as well as non-linear.
In addition to the defining criteria just discussed, mechanisms are
occasionally defined as unobservable, and as processes that only occur in a
system. In both cases I would argue that just as mechanisms can be, but must not
be linear, they also can be, but must not be unobservable and part only of
systems. The view that mechanisms are unobservable is held, for instance, by
Mahoney. For him, "[c]ausal mechanisms are posited relations or
processes that the researcher imagines to exist", they are
"unobservables" (Mahoney 2001: 581; emphasis added). This view has its
roots in seventeenth and eighteenth century realist philosophy, which reacted to
the failure to actually observe causes in experimental research that had
previously been conceived as external forces.  Observability is, however, a
variable: it varies between segments of reality, and in the natural sciences it
also improves over time with the development of sophisticated research
technology. Social mechanisms are de facto often theoretically constructed, but
they are not necessarily and by definition unobservable. This also seems to be
the position of Bunge (1997, 420: "most mechanisms are hidden") and of
Hedström and Swedberg (1996: 290).
Bunge (1997, 414) defines mechanism as "a process in a concrete
system", and throughout the article he talks only about processes within
systems. If, however, we take the concept of system seriously and define systems
restrictively, it is obvious that mechanisms do not logically presuppose a
systemic context - even if they do play a crucial role in system functioning.
Unless everything social is by definition considered to constitute a system or
to be part of a (social!) system, we must admit that mechanisms can also operate
outside of a systemic context. Just as has been argued for observability, the
embeddedness of mechanisms in a systemic context should be seen as a variable, a
property that may, but need not be there in order to call something a social
3Mechanisms as Causal Links
If the aim of a study is the causal reconstruction of a specific
macro-phenomenon or a class of macro-phenomena (e.g. contentious episodes), the
search for mechanisms starts not with a correlation, but with the identification
of an explanandum. The term "generative mechanism" underlines this
explanatory strategy. Processes generally do not come as discernable,
"given" units; they have no naturally given beginning and end. We
artificially pick out a sequence, a part of the ongoing process, and try to
explain how it has come to the particular point that is our explanandum.
Especially in historical research, the clear specification of the explanandum is
the only methodological justification for making choices about where to begin an
analysis (Büthe 2000: 487-488). The explanandum may be an event like a riot or
a specific policy decision, a rate (e.g. of unemployment), a relational
structure (e.g. neo-corporatism), a statistical distribution (e.g. the
demographic structure), and even a process (e.g. of technological development or
institutional change). In each case, explanation means causal reconstruction, a
retrospective process-tracing that ends with the identification of crucial
There is no agreement in the literature whether the formulation of a
mechanism includes or excludes initial conditions and outcomes, i.e. whether the
term "mechanism" refers to a (recurrent) process from beginning to
end, or only to that part of it which "links" beginning and end.
Machamer, Darden and Craver (2000) use the term explicitly for entire processes;
for them, a mechanism consists of set-up conditions, intermediate activities,
and termination conditions. Hedström and Swedberg (1996) on the other hand use
the term "mechanism" to refer to that part of a process that
"links" cause (or input, as they say) and effect (outcome), or
formally expressed: I - M - O. The mechanisms M serves to explicate an observed
relationship between specific initial conditions and a specific outcome.
Pawson's formula "context - mechanism - outcome" can be understood in
the same way (Pawson 2000). The notion of mechanisms as intervening between I =
the explanans and O = the explanandum takes correlational analysis visibly as
point of departure, and critically develops an alternative to it by adding the
causal link M. But care must be taken not to equate an intervening mechanism
with an intervening variable, as it is used in correlational analysis. As
Mahoney states, quoting seven authors as evidence, "[a] causal
mechanism is often understood as an intervening variable or set of intervening
variables that explain why a correlation exists between an independent and a
dependent variable". But, he continues, "this definition unfortunately
does not go beyond correlational assumptions" (Mahoney 2001, 578). In fact,
an intervening variable is a variable that is added to increase the total
variance explained in a multivariate analysis. Intervening variables are not
process links. 
If a mechanism is represented as linking two events or system states,
contingency resides in the initial (or context) conditions that are not part of
the mechanism itself. The difference between the definition of mechanisms as
processes merely linking, or including, variable initial and terminal conditions
may be moot, but it does reflect two different cognitive interests: the interest
in that which is constant in a mechanism, or the interest in the variability of
its operation. The first perspective, expressed in the I - M - O model, also
underlies Elster's often quoted definition of mechanisms as "frequently
occurring and easily recognizable causal patterns that are triggered under
generally unknown conditions or with indeterminate consequences" (Elster
1998, 45 ). The apparent impossibility to say when a mechanism will be triggered
is the result of not including an important initial condition in its
formulation. A virus cannot start an epidemic in a fully immunized population,
nor is a spark enough to trigger an explosion; the powder must also be dry.
It does not make any difference for a substantive analysis whether outcomes
and initial conditions are included in the formal definition of a mechanism or
not, as long as we look at the whole process and recognize that
"inputs" and "outputs" can vary, making outcomes contingent
on variable initial conditions. The initial conditions in a proposition are
stated explicitly; they are known conditions, and outcomes vary in predictable
ways with changes in these conditions. Of course there is also some contingency
in outcomes following from unknown factors included in the ceteris paribus
clause that holds for mechanism statements as for all except truly universal
propositions, but this is evidently not what the "I" in the I - M - O
model refers to. Though in different ways, both the I - M - O model and Elster's
definition suggest that there is something constant in mechanisms, something
that may not change if the mechanism under review is not to loose its identity
and become a different mechanism altogether. If inputs and outcomes are
permitted to vary, it is the sequence of steps, the causal structure of the
generative mechanism that must remain constant.
4Causal Regression and the Limits of Methodological Individualism
To bring some order into the confusing variety of phenomena called
"mechanisms", it is useful to distinguish between a) the level of
reality they refer to, b) their degree of conceptual abstraction, and c) their
assumed scope of application. If social phenomena are explained by psychological
mechanisms and psychological phenomena by neurological processes, causal
regression from a higher to a lower level of reality is involved. Elements on
different levels of reality can stand in a part-whole relation, like cells to an
organism, or human actors to a social system. System level phenomena are then
explained by the activities of the parts. Mechanisms, accordingly, exist in a
"nested hierarchy": The activity of an entity at a given level may be
looked at (1) in isolation, (2) constitutively, i.e. by identifying the lower
level mechanisms that generate its activity, or (3) contextually, by showing how
it fits into the organization of a higher-level mechanism (Craver 2001, 65-71).
In the philosophy of science it is generally held that "(f)or a
higher-level law to be mechanically explicable, it must be realized by some
lower-level mechanism" (Glennan 1996, 62).
In contrast, conceptual abstraction takes place on a single level of reality;
the concepts "United Kingdom in 1990", "twentieth century West
European states", and "modern states" all refer to the same kind
of social unit. It is possible to develop highly general concepts of mechanisms
if we pare down complex concrete processes to the bare bones of basic
interaction types, such as cooperation, competition, negotiation and
subjugation. Karlsson (1958), Elster (1989), and Bunge (1997) have all spoken of
such basic social processes and called them mechanisms. Propositions about
mechanisms can form conceptual hierarchies, ranging from the particular to the highly
general. "Path dependent technological innovation", "increasing
returns", and "positive feedback" are increasingly general
concepts that can be applied to the same case, for instance the frequently cited
QWERTY case of the typewriter keybord (David 1985).
More abstract concepts are often called more general, and indeed their scope
of application is wider than that of their more specific sub-categories. There
are more cases of positive feedback, for instance, than of path dependent
technological innovation, more cases of "cooperation" than, say, of
neo-corporatism. But there are also possible differences in the scope of
application independent of the degree of conceptual abstraction. Such
differences would be based on differences in the inherent regularity between,
for instance, physical reality on the one hand, where (near-)universal
regularities can be found, and organisms and social systems on the other hand.
In fact, this has been argued by biologists and social scientists alike.
Conceivably, the general concept of negative feedback, the threshold-dependent
balancing of activating and inhibiting forces, has a more restricted scope of
application in the social than in the organic world. Any given mechanism
statement can, then, be characterized by a) the level of reality it refers to,
b) its degree of conceptual abstraction, and c) the scope of its claimed
applicability at a given level of abstraction. Of these distinctions, the first
plays the most significant role in the discussion about mechanisms.
Complex social units are seen as part-whole hierarchies, with human actors
and their actions as elements. Hedström and Swedberg (1996, 299) state
peremptorily that "there exist no macro-level mechanisms". According
to Büthe (2002, 483), causal mechanisms "are usually derived from very
general theories of the constraints, motivations, and cognitive processes
employed in decision making and thus shaping human agency". Little argues
that social regularities are emergent phenomena not directly governed by any
laws; the only governing regularities in social reality are regularities of
individual agency (Little 1993, 188). These quotes express the basic tenet of
methodological individualism; it calls for causal regression in the explanation
of social macro-phenomena on the assumption that system properties are not
caused directly by other system properties, but by the activities of the system
The principle of methodological individualism is often illustrated by the
macro-micro-macro model of sociological explanation. Developed by Coleman (1986,
1990) and adopted among others by Esser (1993, 2002) and Hedström and Swedberg
(1996), this model states that the connection between two macro phenomena (e.g.
protestant ethic and capitalist economy, improved social conditions and
revolution) must be explained by going down to the level of motivated human
beings and their activities. The model can also be applied to processes of
change in a given social structure or institution. Micro1 stands for individual
reactions to situational givens determined by Macro1, Micro2 for the behavior
thus induced. The "fixed kernel" (Coleman 1990, 11) of the model at
the micro level is a theory of action, whether perceived in terms of rational
choice or in terms of interpretive social science (Little 1991: 11); a mechanism
based account is quite compatible with different social theories of action. Some
authors (as for instance Elster 1989) go even a step further and explain social
action by cognitive and other psychological mechanisms (e.g.
Adapted from Coleman (1986, 1990).
For purely pragmatic reasons, it is of course often not
possible to go down to the level of individual behavior in empirical research
that tries to account for a macro-event or change process. If the macro-effect
to be explained is for instance the result of bargaining among formal
organizations (unions, business organizations, governments) one would not go
down to the level of the individual organization members to explain the
strategic choices of the corporate actors - not only for pragmatic reasons, but
also because causal regression to the micro level of individual action is not
necessary as long as it is possible to attribute actor quality to larger social
units. Stinchcombe makes a similar point when he doubts the explanatory surplus
value of seeking an explanation of collective patterns of magical practice at
the individual level. He concludes:
Where there is rich information on
variations at the collective or structural level, while individual-level
reasoning (a) has no substantial independent empirical support and (b) adds no
new predictions at the structural level that can be independently verified,
theorizing at the level of [individual level] mechanisms is a waste of
time. (Stinchcombe 1991: 379-380).
But even where going down to the level of individual
behavior is feasible, it would be a fateful misunderstanding to believe that
macro-phenomena follow directly from motivated individual behavior.
Let us return for a moment to the I - M - O model of
mechanisms. If we project this model onto the full macro-micro-macro model of
sociological explanation, "M" refers to the whole sequence of steps
linking Macro 1 and Macro 2. However, the I - M - O model can also be applied
separately to all of the three relations making up the macro-micro-macro model.
Thus, the outcome "O" in the I -M - O model can be an action situation
as well as a type of behavior (such as divorcing; see Esser 2002), or a macro
phenomenon. Looked at more closely, the macro-micro-macro model of sociological
explanation therefore consists of three different types of mechanisms:
macro-micro, micro-micro, and micro-macro. Macro-micro mechanisms are involved
in the generation of action situations; micro-micro mechanisms generate
individual behavior; and micro-macro mechanisms generate macro-phenomena. These
three kinds of mechanisms are the basis of the typology most often adopted by
authors who try to make typological distinctions at all, something that is the
exception rather than the rule.
Prominent among those using this threefold typology are
Hedström and Swedberg (1996), who speak of situational (macro-micro),
individual action (micro-micro), and transformational (micro-macro) mechanisms
(Hedström/Swedberg 1996, 296-298; see also Müller 2001, 55). An independently
developed threefold typology is offered by Tilly (2001) and by McAdam, Tarrow
and Tilly (2001), who distinguish between environmental, cognitive, and
relational mechanisms. Environmental mechanisms (such as resource depletion)
produce changes in "the conditions affecting life"; cognitive
mechanisms refer to psychological mechanisms driving specific kinds of behavior;
and relational mechanisms "alter" the "connections among people,
groups, and interpersonal networks" (Tilly 2001: 26). Looked at
superficially, this typology seems very similar to the Hedström and Swedberg
typology. Cognitive mechanisms driving specific kinds of behavior clearly fall
into the category of micro-micro mechanisms. It is less evident that
environmental mechanisms correspond to the category of macro-micro mechanisms:
They do (by definition) affect action situations, but possibly by non-social
factors such as resource depletion. Relational mechanisms, finally, may seem to
fall into the category of Hedström and Swedberg's transformational mechanisms.
But if one looks more closely at their substantive content, an important
difference to the dominant conceptions of micro-macro mechanisms becomes
visible. As the term indicates, relational mechanisms emphasize relations, i.e.
structures, and not only individual action. This holds for such basic mechanisms
as competition (considered as interaction process), and it also holds for the
mechanism of brokerage that plays an important role in the social processes
leading to contentious episodes analyzed by McAdam, Tarrow and Tilly. Brokerage
is not defined as a specific type of action (brokering), but as the process
linking "two or more unconnected social sites by a unit that mediates their
relation with one another and/or with yet other sites" (McAdam, Tarrow,
Tilly 2001, 26).
Relational mechanisms are of crucial importance for the
causal reconstruction of social macro-phenomena. This directs attention to a
critical weakness of the macro-micro-macro model. As graphically depicted,
Coleman's model has a built-in bias in favor of individual action (or agency).
Before re-emerging in the description of the outcome, structural and
institutional factors appear in the model only as determinants of the action
situation of individuals. The micro-macro mechanism seems to generate
macro-effects directly from individual action. Such a notion fits quite well
where macro-phenomena appear as emergent effects of the interdependent, but
uncoordinated actions of many individuals, as for instance in diffusion or
mobilization processes. Not surprisingly, it is exactly such processes that not
only Coleman himself, but also Boudon (1979) and most of the authors in the
Hedström and Swedberg (1998) collection concentrate on. The same holds for
Karlsson (1958), who speaks generally of "interaction mechanisms", of
which he distinguishes two subtypes: diffusion mechanisms and choice mechanisms.
The latter are determined by the preferences and properties of actors, and
generate typically distributional structures such as endogamy or spatial
segregation. Even Elster (1989), where he goes beyond the explication of
psychological mechanisms, concentrates on aggregate effects  of motivated
However, the identification of "micro" with
individual action implicitly eliminates structural features from the core of the
mechanism directly responsible for a macro-phenomenon. True, Coleman (1990, 11)
notes discursively that individual action produces different social phenomena
"when located in different social contexts", and lists "various
ways in which actions combine to produce macro-level outcomes" (Coleman
1990, 11, 20), but no effort is made to include structural features explicitly
in the micro-macro part of the model.  In fact, however, macro-structures, i.e.
relational constellations that may, but need not be institutionally based, are
integral parts of the processes generating social macro-phenomena; they are in
fact the decisive parts.
This is evident even for aggregate (emergent, interaction)
effects following from the actions of the individuals in a given population. In
the diffusion of an innovation, a rumor, or a disease, the receptivity of each
individual determines only whether, if contacted, she will adopt an innovation,
believe and pass on a rumor, or fall ill. But the shape of the whole process,
how quickly it extends, how highly it peaks or whether it breaks off at an early
point is entirely dependent upon the contact structure in the population and the
profile of receptivity over all individuals - both undoubtedly macro-structural,
and both undoubtedly components of the generative mechanism. This has been
clearly recognized by Granovetter who, in his analysis of threshold models of
collective behavior, emphasizes the need to "specify the impact of social
structure on collective outcomes" (Granovetter 1978, 1430). The mechanism
generating the macro-effect "market equilibrium" also depends on
structural features, such as the existence of a plurality of competing producers
and the absence of political price fixing; the rational decisions of individuals
to offer or buy are the "material stuff" of the process, but its shape
is determined by these structural elements. Even the famous "tragedy of the
commons" does not simply result from the rational behavior of individuals
who discount future (or collective) costs against present (or private) profit;
this action orientation leads to a "tragedy" only if land for grazing
is institutionally defined as common property. Arguing along this line, Ostrom
generally emphasizes the importance of institutional rules for the occurrence
and solution of common pool resource problems; more recently she even includes
structural properties of the social groups in her analysis (Ostrom 1990, 1999).
In all of these cases, specific structural (or institutional) features are
decisive for the generation of aggregate macro-effects.
This is even more evident when we deal with outcomes
resulting from specific types of actor constellations. A classical example is
Elias' Königsmechanismus which operates in the sociogenesis of the modern state
(Elias 1969). The basis of this mechanism is a hierarchical relationship between
a central authority and a plurality of lower level power centers envious of
their autonomy. As the power of the central authority increases, the lower level
units shift from competition among each other to cooperation, thus weakening the
central authority; this eases pressure on the lower level units, which revert to
competition among each other. This particular actor constellation thus generates
a repeated oscillation between centralization and decentralization. Or to take a
present-day example: policy blockades (as outcomes) that occur in federal states
are the consequence of a structure of constitutionally defined veto points that
offer a regional or political minority the opportunity to deny the passage of
legislation. Structural factors are also decisive when experts can find a
problem solution on the basis of technical arguments in a negotiation structure
where the resolution of distributional conflicts is organizationally separated
from the technical discourse. Of course structures exert their effect through
the actions of individuals, but assuming a general action orientation of
individuals (for instance rational choice), it is the nature of the structural
arrangements within which they act that determines the effect. If the
explanandum is a macro phenomenon, or the connection between two macro phenomena
such as a contribution based welfare system and a growing unemployment rate, the
main cognitive challenge is therefore to identify the structural and
institutional features that process (or organize, in the terminology of Craver)
the actions of different actors so as to produce the macro effect.
5Social Mechanisms as Theoretical Building Blocks
The preceding discussion has hopefully dispelled some of
the confusion besetting the use of the mechanism concept in the social sciences.
At this point we can return to the question that originally motivated this
exercise, i.e. to clarify the - presumably crucial - role that propositions
about mechanisms play in the causal reconstruction (and thus explanation) of
To put the question this way means to start with
circumscribed empirical fields, not to search for a general social theory à la
Niklas Luhmann, in which case we would try to find the most general mechanisms
that operate in the social world. Such an effort might in the end lead to some
encompassing analytical framework like the one developed by Leopold von Wiese,
the major representative of German formal sociology, who classified all social
processes into two basic categories, processes of Zueinander (coming together)
and processes of Auseinander (drawing apart) (von Wiese 1933). But "generic
mechanisms can explain no particular facts", as Bunge (1997: 451) warns us.
To spell out the general interactive dynamic leading to cooperation abstractly
defined helps little to explain how cooperation between organized business and
organized labor is generated in a neo-corporatist structure of economic policy
making. It is not possible to build a substantive theory out of context-free,
general mechanisms. Mechanisms explaining concrete macro-phenomena must be much
The starting point of the search for mechanisms operating
in a specific field is always an observed or suspected regularity, a
correlation, or a puzzling event, structure, or process. Mechanisms are links in
theory; they are causal propositions that explain specific outcomes by
identifying the generative process which, given certain initial conditions,
produces them. If social mechanisms are to explain observed phenomena or
relationships, this means that the latter are logically prior: The
"what" logically precedes the "how"-question. Field-specific
theories can include propositions about social mechanisms, but by themselves,
these propositions do not make a coherent theory. This is in fact recognized in
definitions of theory as that offered by Kiser and Hechter (1998), who mention
mechanisms as parts of theories. Statements about mechanisms can therefore well
complement an analysis based on statistical correlations. In fact, this is how
they are often discursively used, though mostly more ad hoc than in a systematic
manner. There are also cases of sophisticated correlation analysis that come
quite close to an analysis in terms of mechanisms without ever using that word
(e.g. Hoover 1990). The contrast between correlational (multivariate) and
mechanistic approaches is by no means as stark as some of the latter's advocates
maintain. To pit analysis in terms of mechanisms against the search for
correlations is mistaken.
Processes identified in the causal reconstruction of a
particular case or a class of macro-phenomena are transformed into mechanism
statements if their causal structure is recognized to apply also to other
(classes of) cases. The mobilization process observed in a fund-raising campaign
for a specific project can for instance be generalized to cover other outcomes
such as collective protest, or a patriotic movement inducing young men massively
to enlist in a war. A particular case of technological innovation like the
QWERTY keyboard may similarly be recognized as a case in which an innovation
that has initially gained a small competitive advantage crowds out technological
alternatives in the long run. This is already a mechanism of a certain
generality, but it may be generalized further to the mechanism of
"increasing returns", which does not only apply to technological
innovations but has also been used in the analysis of institutional stability
and change (Pierson 2000, Thelen 1999). "Increasing returns", of
course, is a sub-category of positive feedback, an even more general mechanism
that also operates in the bankruptcy of a firm caused by the erosion of trust,
or in the escalation of violence in clashes between police and demonstrators
(Nedelmann/Mayntz 1987). If we aim to identify social mechanisms specific enough
to have explanatory value for particular observed outcomes or relationships, but
at the same time general enough to apply in different empirical fields, it is
necessary to spell out the range of initial conditions that, through a process
with a given causal structure, can generate a range of different outcomes. In
this way, a tool-box of more general mechanism models could be built up. And
while no particular event can be derived from such a general concept as
"positive feedback", the concept can stimulate the researcher to look
out for a specific type of causal dynamic in his empirical case or cases.
The majority of macro-phenomena that especially political
scientists deal with cannot be explained by applying one particular mechanism
model. Instead, the causal reconstruction of macro-phenomena such as non-violent
regime change, rising unemployment, or democratization involves a chain of
different mechanisms that jointly generate the outcome. Not all of the component
mechanism of such a process will be social in the strict sense; in the processes
analyzed by McAdam, Tarrow and Tilly, basically psychological (cognitive)
mechanisms as, for instance, "identity shift" are important parts of
the causal chain. The higher-order processes may themselves be patterned and
hence qualify as second-order mechanisms, but whether they do or not is an
empirical question. McAdam, Tarrow and Tilly (2001) for instance describe the
process of democratization as a second-order process that is composed of a
series of mechanisms which may be joined together in different ways, but still
lead to a comparable "terminal condition". Substantive theories,
whether they deal with contentious episodes, institutional stability and change,
or varieties of capitalism, typically involve a plurality of mechanisms of a
relatively high degree of specificity.
The problem is that our theoretical tool-boxes for
different types of mechanisms are very unevenly filled. We have a good-sized, if not very orderly tool-box of mechanism models for different forms
of collective behavior - collective in the sense that the uncoordinated, but
interdependent actions of many individuals generate aggregate effects. Examples
are models of linear and non-linear diffusion, the mechanism underlying spatial
segregation in urban housing, the market mechanism, and the mechanism of
mobilization where not only thresholds, but also a "production
function" (i.e. how many must participate to produce the effect) plays a
role . We have as yet no similarly filled tool-box of mechanisms where specific
types of corporate actor constellations and relational structures play the
crucial role. Several such mechanisms have been identified by McAdam, Tarrow and
Tilly (2001); the brokerage mechanism already mentioned is only one example.
Concrete macro-processes involve a large variety of structural and institutional
features which it is very difficult to systematize. They range from Simmel's
tertius gaudens, different network configurations and different kinds of power
structure (concentrated or fragmented, centralized or decentralized, single or
multi-level etc.), to the rules for the processing of votes in election systems.
In this sea of most diverse particulars, game theory is an island of general
concepts and models of constellation effects. In game theory it is the pay-off
structure that determines whether (rational) actors cooperate. A game like
Prisoner's Dilemma or Battle of the Sexes is a relatively simple mechanism,
involving mainly the pay-off structure and the rational orientation of players
as initial conditions that determine the strategy choices of actors, whose
combination in turn produces the outcome of the interaction. But as often
pointed out, many actor constellations cannot meaningfully be modelled as games.
While neo-corporatist bargaining might be explained in terms of strategic
interdependence (i.e. game models), the generation of the basic precondition of
such bargaining, i.e. the existence of a particular structure of interest
organizations, is the result of a much more complex process, involving
technological and legal innovations, a specific form of social differentiation,
and authoritative political intervention.
With the exception of game theory, the literature is still
devoid of attempts to treat diverse kinds of actor constellations in different
fields of macro-social research as systematically as has been done for the
emergent effects of collective behavior. If different structural configurations
and actor constellations generate indeed typical kinds of social dynamic, it
would be worth while to search for mechanism models that go beyond collective
behavior and the production of aggregate effects on the one hand and game theory
on the other hand. The problem is that in most empirical studies in which
structural configurations and actor constellations play a crucial role, very
little effort is devoted to distil mechanism models from the analysis. The work
of McAdam, Tarrow and Tilly (2001) on contentious episodes is a notable
exception. Other fields that might be subjected to a secondary analysis with a
similar intention in mind include research on regime transformation with its
focus on change processes, research on the varieties of capitalism with its
focus on processes of systemic interdependence, studies in historical
institutionalism with their focus on institutional continuity and change, and
generally, analyses of policy processes in single- and multi-level political
systems. It would be of great theoretical interest to see to what extent the
social mechanisms identified in such different fields are isomorphic and can be
generalized, or remain specific to the type of explanandum. This article thus
concludes as befits a state-of-the-art analysis: with a call for further work.
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Following Coleman (1964), mechanisms are occasionally called
"sometimes-true theories" to distinguish them from laws; see for
instance Stinchcombe 1998: 267. This label, however, applies equally to
correlational propositions with an explicit ceteris paribus clause. Mahoney
(2001: 578) may make the same point when he argues that the notion of mechanisms
as mid-level theories does not clearly differentiate the concept from that of a
probabilistically formulated hypothesis, i.e. a kind of hypothesis that belongs
squarely to correlational analysis.
For a more extended discussion see Somers (1998: 725-726)
and Calhoun (1998: 851, footnote 5).
The confusion is both semantic as well as related to
research technology. The word intervene can be used with different meanings,
including to say that a process or mechanism "linking" cause and
effect "intervenes" between them. And social processes such as
democratization, economic growth, or mobilization can be operationalized in the
form of a quantitative variable. The dividing line between analyses in terms of
correlations and in terms of mechanism, while logically clear, can practically
be quite thin.
Following Boudon (1984), who in discussing such effects
repeatedly speaks of agrégation d'actions individuelles, I use this term not
for statistical properties (e.g. mobility rate, income distribution), but for
the results of collective action processes producing unintended macro effects
such as a panic, a segregated settlement structure, or an unanticipated
political revolution (see Kuran 1989).
In Esser's explanatory sociology, structural and
institutional factors not included in Macro 1 are seen to play the role of
intervening meso-level variables in the transformational mechanism (Esser 1993),
but this does does not really fit a model that strictly separates macro =
structural from micro = behavioral.
For a survey of different kinds of discontinuous processes
see Mayntz 1997 (first 1988).
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