Scepticism about Knowledge of Content

Abstract

Externalism about content threatens to undermine privileged access and to generate scepticism concerning knowledge of one's own mental states. Suppose that the contents of one's mental states are, in part, determined by physical and social states of affairs external to one's mind and body. This is, roughly, the externalist, 'anti-individualist' view of content which has its roots in Hilary Putnam's twin earth thought experiment and which has been most extensively developed by Tyler Burge.' Some have worried that this externalist view has the consequence that in order to know the contents of one's own mental states, one must know the pertinent external, content-determining physical and social states of affairs.2 If externalism about content does have this consequence, then one cannot know the contents of one's states in any direct or privileged way, since knowledge of content would have to be based upon knowledge of the external, content-determining circumstances, which knowledge is as accessible to others as it is to oneself. Worse, if one lacked knowledge of the key external circumstances, then one would altogether lack knowledge of the contents of one's own states, even knowledge based on inference. John Heil argues that externalism about content neither generates scepticism nor undermines privileged access.3 In this paper, I will attempt to clarify the reasons behind scepticism about knowledge of content and to explain why Heil's defence of externalism fails to answer the sceptic. According to externalism about content, the following is possible: person S and his twin S* are physically, behaviourally, functionally, phenomenologically, and introspectively indistinguishable through time even though some of S's mental states differ in content from the corresponding 'twin' states of S*, this difference arising from differences between the two thinkers' external physical (or social) environments. For example, when earthling S utters the sentence 'Water is wet', it expresses his thought that water is wet. But when S*, a twin earthling, utters the sentence on twin earth, replete with XYZ instead of H20, it expresses a different thought from S's, namely the thought that twater is wet. Twin earth is often conceived as a (part of) a possible world different from the actual world. But consider a single possible world containing both earth and twin earth, existing in spatio-temporal relation to each other. In the two-world scenario, S and his counterfactual counterpart S* are phenomenologically and introspectively indistinguishable: things seem exactly the same to them, point for point. In the oneworld scenario, suppose that S is, unbeknownst to him, transported from his