Semantic Basis of Externalism Revisited

This article aims to show that, contrary to what Fred Dretske in Naturalizing the Mind and some others are claiming, compatibility between externalism and Privileged Access to Attitude Content (PAC) is one of the basic problems. It describes some approaches to the solution of this problem which follow from admitting the validity of Michael McKinsey's reductio ad absurdum argument. McKinsey has outlined the challenge for externalists which concerns illusion of sameness of meaning in his 1991 paper "Anti-Individualism and Privileged Access". In Putnam's Twin Earth case, speakers of both earths enjoy the following illusion: "water" means something different on Earth and on Twin-Earth, but this difference might not be accessible to them. The punch line of McKinsey's case runs as follows: if the contents of our thoughts are determined in part by our relations to the environment, then one might think that external observations are needed in order to know what we think. But self-knowledge does not come about through empirical investigations. So either contrary to appearance we do not really know the contents of our own thoughts, or, if we do, externalism is false. If both externalism and the thesis of privileged access were true, then we could have a priori knowledge of certain contingent matters of empirical fact. But the idea that we could have such a priori knowledge is absurd; therefore, one or both externalism and the thesis that we have privileged access to our own mental states are false. The paradox comes with the claim that if thesis of privileged access and externalism are knowable a priori, then we can know contingent external propositions (e.g. that "Water exists") a priori as well. We get this from a plausible principle: the set of things we know is closed under entailment, so we know that a given claim is true upon recognizing, and accepting thereby, that it follows from what we know. To avoid commitment to such an absurd consequence externalists like Michael Tye who endorse PAC commit themselves to rejecting the a priori status of externalism. An argumentation in this vein is supposed to run into the problem raised by Paul Boghossian in "What the Externalist Can Know A Priori". I argue that it is controversial whether the inhabitants of Dry Earth possess the concept of water. I outline a version of strong or concept-possession externalism which evades this kind of issues.

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