A note on global descriptivism and Putnam's model-theoretic argument

Abstract

According to Putnam’s model-theoretic argument, an epistemically ideal theory cannot fail to be true. Lewis contends that all the argument really shows is that an epistemically ideal theory must be true provided a certain theory of reference—which he terms Global Descriptivism—is the whole truth about reference, which he emphatically denies. In this note it is argued that Lewis grants Putnam too much. However implausible Global Descriptivism may be as a comprehensive account of reference, on what appears to be the only reasonable construal of it Global Descriptivism does not imply that an epistemically ideal theory must be true. Define Realism as the thesis that even an epistemically ideal theory of the world is not guaranteed to be true. Putnam’s model-theoretic argument ([5], [6]) argues against this thesis: an epistemically ideal theory cannot fail to be true, so the argument’s conclusion reads. Lewis, in his [3], contends that all the argument really shows is that an epistemically ideal theory must be true provided a certain very weak theory of reference—which he terms Global Descriptivism—is the whole truth about reference. And this Lewis emphatically denies. In this note I distinguish two readings of Global Descriptivism and argue that one of these must be unacceptable to all parties in the debate whereas the other may well be acceptable, not only to Putnam but (at least as one of the principles governing reference) also to Realists. Subsequently it is shown that Putnam’s argument only goes through on the first, unacceptable reading of Global Descriptivism; on the second reading Putnam’s conclusion is unwarranted even if Global Descriptivism were the whole story about reference. Putnam’s model-theoretic argument is so well-known that it hardly requires recounting. I therefore only very briefly rehearse its main moves. Let T be an epistemically ideal theory. It is formulated in a first-order language L(T ) that is assumed to consist of an observational and a theoretical part. That T is epistemically ideal means (i) that it satisfies all operational constraints (meaning, roughly, that it is in accordance with all observations) and (ii) that it exhibits every conceivable theoretical virtue. T is further assumed to assert the world to be infinite, and to be right in this respect. To start take a partial