Causation

Practically, causation matters. Juries must decide, for example, whether a pregnant mother's refusal to give birth by cesarean section was the cause of the death of one of her twins. Policy makers must decide whether violence on TV causes violence in life. Neither question can be coherently debated without some theory of causation. Fortunately (or not, depending on where one sits), a virtual plethora of theories of causation have been championed in the third of a century between 1970 and 2004.

Before the sketch of a few of the major theories, however, consider what one might want out of a theory of causation. First, although one can agree that causation is a relation, what are the relata? Are causes and effects objects, like moving billiard balls? Are they particular events, like the Titanic hitting an iceberg in 1912? Or are they kinds of events, like smoking cigarettes and getting lung cancer? As it turns out, trying to understand causation as a relation between particular objects or events is quite a different task than trying to understand it as relation between kinds of occurrences or events.

Second, one wants a theory to clarify, explain, or illuminate those properties of causation that one can agree are central. For example, whatever causation is, it has a direction. Warm weather causes people to wear lighter clothing, but wearing lighter clothing does not cause warm weather. A theory that fails to capture the asymmetry of causation will be unsatisfying.

Third, one knows that in many cases one thing can occur regularly before another, and thus appear to be related as cause and effect, but is in fact the effect of a common cause, a phenomenon called spurious causation. For example, flashes of lightning appear just before and seem to cause the thunder-claps that follow them, but in reality both are effects of a common cause: the superheating of air molecules from the massive static electric discharge between the earth and the atmosphere. A good theory of causation ought to successfully separate cases of real from spurious causation.

The history of thinking on causation from 1970 to 2004 can be organized in many ways, but the one that separates matters best, both temporally and conceptually, is captured eloquently by Clark Glymour:

Philosophical theories come chiefly in two flavors, Socratic and Euclidean. Socratic philosophical theories, whose paradigm is The Meno, advance an analysis (sometimes called an "explication"), a set of purportedly necessary and sufficient conditions for some concept, giving its meaning; in justification they consider examples, putative counterexamples, alternative analyses and relations to other concepts. Euclidean philosophical theories, whose paradigm is The Elements, advance assumptions, considerations taken to warrant them, and investigate the consequences of the assumptions. Socratic theories have the form of definitions. Analyses of "virtue," "cause," "knowledge," "confirmation," "explanation," are ancient and recent examples. Euclidian theories have the form of formal or informal axiomatic systems and are often essentially mathematical: Euclid's geometry, Frege's logic, Kolmogorov's probabilities,.… That of course does not mean that Euclidean theories do not also contain definitions, but their definitions are not philosophical analyses of concepts. Nor does it mean that the work of Euclidean theories is confined to theorem proving: axioms may be reformulated to separate and illuminate their contents or to provide justifications (n.p.).

For causation, Socratic-style analyses dominated from approximately 1970 to the mid-1980s. By then, it had become apparent that all such theories either invoked noncausal primitives that were more metaphysically mysterious than causation itself, or were circular, or were simply unable to account for the asymmetry of causation or to separate spurious from real causation. Slowly, Euclidean style theories replaced Socratic ones, and by the early 1990s a rich axiomatic theory of causation had emerged that combined insights from statisticians, computer scientists, philosophers, economists, psychologists, social scientists, biologists, and even epidemiologists.