Realism, Underdetermination, and a Causal Theory of Evidence

I shall be concerned in this paper to defend scientific realism against the thesis that the structure of the scientific theories we accept is radically underdetermined by any possible experimental evidence. In the course of this discussion I will have occasion to advance an account of scientific evidence which, I believe, extends in interesting ways the considerations which have led some philosophers to advance theories of knowledge. By scientific realism I mean the doctrine that the sort of evidence which ordinarily counts in favor of the acceptance of a scientific law or theory is, ordinarily, evidence for the (at least approximate) truth of the law or theory as an account of the causal relations obtaining between the entities quantified over in the law or theory in question. On this view, experimental evidence for a theory which describes causal relations between (that is, unobservable) entities is evidence not only for the correctness of the observational consequences of the theory, but is also evidence that the particular causal relations in question explain the predicted regularities in the behavior of observable phenomena. Of course this does not mean that, in the general case, experimental evidence for a theory is evidence that the causal relations it describes between observable or theoretical entities exhaust those causal relations obtaining between them (although this might be the case in the case of theories which were suitably complete). But it does entail that experimental evidence for a theory is evidence that those causal relations it describes, and not others incompatible with them, operate to produce the regularities in observable phenomena which the theory predicts. This last feature of scientific realism has been thought by many philosophers in the tradition of logical empiricism to embody a fatal weakness. They argue that, given any theory which contains