The Problem of Armchair Knowledge

1. McKinsey’s reductio argument: Externalism and self-knowledge In ‘Anti-individualism and privileged access’ (1991), Michael McKinsey asks us to consider the following three propositions, where ‘E’ says that some particular externalist condition for thinking that water is wet is met: (1) Oscar knows a priori that he is thinking that water is wet. (2) The proposition that Oscar is thinking that water is wet conceptually implies E. (3) The proposition E cannot be known a priori, but only by empirical investigation. He then argues that (1), (2) and (3) constitute an inconsistent triad as follows (1991, p. 15): Suppose (1) that Oscar knows a priori that he is thinking that water is wet. Then by (2), Oscar can simply deduce E, using premisses that are knowable a priori, including the premiss that he is thinking that water is wet. Since Oscar can deduce E from premisses that are knowable a priori, Oscar can know E itself a priori. But this contradicts (3), the assumption that E cannot be known a priori. Hence (1), (2), and (3) are inconsistent. McKinsey’s conclusion is that ‘anti-individualism is inconsistent with privileged access’ (ibid.). In a more recent paper (2002), McKinsey sets out very clearly the principles about privileged access and externalism on which his argument depends. First, (1) is a consequence of a doctrine of privileged access or first-person authority about the contents of our thoughts: Privileged access to content (PAC) It is necessarily true that if a person x is thinking that p, then x can in principle know a priori that he himself, or she herself, is thinking that p. Second, if we take E to be an externalist condition in the sense that it ‘asserts or implies the existence of contingent objects of some sort external relative to Oscar’ then (2) is a consequence of a doctrine of semantic externalism applied to the predicate ‘is thinking that water is wet’: Semantic externalism (SE) Many de dicto-structured predicates of the form ‘is thinking that p’ express properties that are wide, in the sense that possession of such a property by an agent logically or conceptually implies the existence of contingent objects external to that agent.