Causal mechanisms: The processes or
pathways through which an outcome is brought into being. We explain an outcome by offering a
hypothesis about the cause(s) that typically bring it about. So a central ambition of virtually all
social research is to discover causes.
Consider an example: A rise in prices causes a reduction in
consumption. The causal mechanism
linking cause to effect involves the choices of the rational consumers who
observe the price rise; adjust their consumption to maximize overall utility;
and reduce their individual consumption of this good. In the aggregate, this rational behavior at the individual
level produces the effect of lower aggregate consumption.
There are two broad
types of theories of causation: the Humean theory (“causation as regularities”)
and the causal realist theory (“causation as causal mechanism”). The Humean theory holds that causation
is entirely constituted by facts about empirical regularities among observable
variables; there is no underlying causal nature, causal power, or causal
necessity. The causal realist
takes notions of causal mechanisms and causal powers as fundamental, and holds
that the task of scientific research is to arrive at empirically justified
theories and hypotheses about those causal mechanisms. Consider these various assertions about
the statement, “X caused Y”:
·
X
is a necessary and/or sufficient condition of Y.
·
If
X had not occurred, Y would not have occurred.
·
The
conditional probability of Y given X is different from the absolute probability
of Y (P(Y|X) <> P(Y)).
·
X
appears with a non-zero coefficient in a regression equation predicting the
value of Y.
·
There
is a causal mechanism leading from the occurrence of X to the occurrence of Y.
The central insight of causal realism is that the final criterion is in fact the most fundamental. According to causal realism, the fact of the existence of underlying causal mechanisms linking X to Y accounts for each of the other criteria; the other criteria are symptoms of the fact that there is a causal pathway linking X to Y.
Causal
reasoning thus presupposes the presence of a causal mechanism; the researcher
ought to attempt to identify the unseen causal mechanism joining the variables
of interest. And this list of
causal criteria suggests a variety of ways of using available evidence to test
or confirm a causal hypothesis: apply Mill’s methods of similarity and
difference as a test for necessary and sufficient conditions, examine
conditional probabilities, examine correlations and regressions among the
variables of interest, and use appropriate parts of social theory to
hypothesize about underlying causal mechanisms. Causal realism insists, finally, that empirical evidence
must be advanced to assess the credibility of the causal mechanism that is
postulated between cause and effect.
What
is a causal mechanism? A causal
mechanism is a sequence of events or conditions, governed by lawlike
regularities, leading from the explanans to the explanandum. Wesley Salmon puts the point this way:
“Causal processes, causal interactions, and causal laws provide the mechanisms
by which the world works; to understand why certain things happen,
we need to see how
they are produced by these mechanisms” (Salmon 1984 : 132). Nancy Cartwright likewise places real
causal mechanisms at the center of her account of scientific knowledge. As she and John Dupré put the point,
“things and events have causal capacities: in virtue of the properties they
possess, they have the power to bring about other events or states” (Dupré and Cartwright
1988). And most fundamentally, Cartwright
argues that identifying causal relations requires substantive theories of the
causal powers or capacities that govern the entities in question. Causal relations cannot be directly
inferred from facts about association among variables.
The
general nature of the mechanisms that underlie social causation has been the
subject of debate. Several broad
approaches may be identified: agent-based models, structural models, and social
influence models. Agent-based
models follow the strategy of aggregating the results of individual-level
choices into macro-level outcomes; structural models attempt to demonstrate the
causal effects of given social structures or institutions (e.g. the tax
collection system) on social outcomes (levels of compliance); and social
influence models attempt to identify the factors that work behind the backs of
agents to influence their choices.
Thomas Schelling’s apt title “Micromotives and Macrobehavior” (Schelling 1978) captures the logic of
the former approach, and his work profoundly illustrates the sometimes highly
unpredictable results of the interactions of locally rational-intentional
behavior. Jon Elster has also shed
light on the ways in which the tools of rational choice theory support the
construction of largescale sociological explanations (Elster 1989). Emirbayer and Mische provide an
extensive review of the current state of debate on the concept of agency (Emirbayer and Mische
1998). Structuralist and social influence
approaches attempt to identify socially salient influences such as institution,
state, race, gender, educational status, and to provide detailed accounts of
how these factors influence or constrain individual trajectories—thereby
affecting social outcomes.
Cartwright, Nancy. 1989.
Nature’s Capacities and their Measurement. Oxford: Oxford University Press.
Dupré, John, and Nancy
Cartwright. 1988. Probability and Causality: Why Hume and Indeterminism Don’t
Mix. Nous
22:521-536.
Elster, Jon. 1989. The
Cement of Society: A Study of Social Order. Cambridge: Cambridge University Press.
Emirbayer, Mustafa, and
Ann Mische. 1998. What Is Agency? American Journal of Sociology 103 (4):962-1023.
Little, Daniel. 1998. Microfoundations,
Method and Causation: On the Philosophy of the Social Sciences. New Brunswick, New
Jersey: Transaction Publishers.
Mackie, J. L. 1974. The
Cement of the Universe; A Study of Causation. Oxford,: Clarendon Press.
Miller, Richard W. 1987.
Fact and Method: Explanation, Confirmation and Reality in the Natural and
the Social Sciences.
Princeton, N.J.: Princeton University Press.
Salmon, Wesley C. 1984. Scientific
Explanation and the Causal Structure of the World . Princeton: Princeton
University Press.
Schelling, Thomas C.
1978. Micromotives and Macrobehavior . New York : Norton.
Encyclopedia of
Social Science Research Methods, edited by Michael Lewis-Beck (University of
Iowa), Alan Bryman (Loughborough University), and Tim Futing Liao. Sage Publications.