derive from the actions of purposive men and women; so what kinds of regularities are available on the basis of which to provide social explanations? A fruitful research framework in the social sciences is the idea that men and women are rational, so it is possible to explain their behavior as the outcome of a deliberation about means of achieving their individual ends. This fact in turn gives rise to a set of regularities about individual behavior that may be used as a ground for social explanation. We may explain some complex social phenomenon as the aggregate result of the actions of a large number of individual agents with a hypothesized set of goals within a structured environment of choice. Social scientists have often been inclined to offer functional explanations of social phenomena. A functional explanation of a social feature is one that explains the presence and persistence of the feature in terms of the beneficial consequences the feature has for the ongoing working of the social system as a whole. It might be held, e.g., that sports clubs in working-class Britain exist because they give working-class people a way of expending energy that would otherwise go into struggles against an exploitative system, thus undermining social stability. Sports clubs are explained, then, in terms of their contribution to social stability. This type of explanation is based on an analogy between biology and sociology. Biologists explain species traits in terms of their contribution to reproductive fitness, and sociologists sometimes explain social traits in terms of their contribution to ‘social’ fitness. However, the analogy is misleading, because there is a general mechanism establishing functionality in the biological realm that is not present in the social realm. This is the mechanism of natural selection, through which a species arrives at a set of traits that are locally optimal. There is no analogous process at work in the social realm, however; so it is groundless to suppose that social traits exist because of their beneficial consequences for the good of society as a whole (or important subsystems within society). So functional explanations of social phenomena must be buttressed by specific accounts of the causal processes that underlie the postulated functional relationships. See also CAUSATION, DECISION THEORY, EXPLANATION , PHILOSOPHY OF SCIENCE , VER – STEHE. D.E.L.