Causation, further themes

4. Causal functionalism

The thought that it may be possible to marry the insights of the counterfactual approach and those of empirical approaches that emphasize the centrality of processes motivates a recent theory (Menzies 1996), which Lewis (2004) has aptly called causal functionalism. The theory applies the Carnap–Ramsey technique for defining theoretical terms to causation (see Ramsey, F. P. §5). It starts with a folk theory of the causal relation consisting of platitudes about the properties that the causal relation has. These platitudes specify the functional role that the causal relation is thought to occupy. It ends by stipulating that the causal relation is the relation, if there is one, that does in fact occupy this specified role.

The folk theory, it is claimed, has three crucial platitudes. First, the causal relation is a relation between wholly distinct or logically independent events. Second, it is a relation that is intrinsic to the event-pairs that instantiate it. Third, it is typically, but by no means invariably, associated with counterfactual dependence. In the vast majority of cases in which an event c causes another event e, the latter event counterfactually depends on the former. However, while this is not true in cases of pre-emption, these are atypical cases where the presence of extrinsic back-up causes frustrates the appropriate counterfactual dependencies.

In sum, then, the conceptual part of the functionalist theory says that the causal relation is the intrinsic relation that is typically associated with counterfactual dependence between distinct events. This is enough for us to single out Suzy’s stone-throwing, and not Billy’s, as the cause of the bottle’s shattering. For an intrinsic physical relation of the kind that typically holds when there is a counterfactual dependence between distinct events connects Suzy’s throw, but not Billy’s throw, with the bottle’s shattering. Of course, it is open to us to conduct an a posteriori investigation of the nature of this intrinsic relation. It may turn out to be the relation that holds between events when there is a transfer of energy-momentum between them. Or more plausibly, if we relativize the theoretical definition of causation to a kind of system, we may find that the intrinsic relation varies from one kind of system to another, sometimes being a physical process, sometimes a non-physical process.

Such a functionalist approach has the virtue of separating out the conceptual and empirical parts of the process of identifying the causal relation. It is also a realist theory in so far as it takes causation to be a structural feature of reality that underlies counterfactual dependence. While a counterfactual dependence between two distinct events generally indicates the existence of a causal relation between events, the causal relation itself is distinct from that counterfactual dependence.