John Collins

Externalism about mental content is the thesis that the contents of an individual's mental states are fixed, not just by the intrinsic characteristics of the individual, but also by the external circumstances of the individual. Externalism has been argued by some to be incompatible with a subject having direct and authoritative introspective knowledge of the contents of his occurrent thoughts, since the introspectable evidence underdetermines the content of the thought. While this has been disputed, there is nearly a consensus that externalism entails that in some circumstances a subject win not be in a position to tell by introspection whether two of her thoughts have the same or different contents. However, in order to infer reliably in accordance with valid inference rules, one must be able to compare the contents of thoughts or premises that one is entertaining. Furthermore, our folk psychological principles of explanation and prediction frequently presuppose that people can compare the contents of their beliefs, desires and intentions when engaged in practical reasoning. If introspective knowledge of comparative content is undermined, it would seem that our norms of rational and folk psychology have been undermined. ;In this dissertation, I consider whether externalism indeed raises the difficulties it is alleged to, and conclude that it does entail that in some circumstances subjects will be unable to recognize invalid inferences as such, and that some folk psychological principles are incompatible with externalism. However, I think that the problems that arise cannot all be laid at externalism's door, and are not serious enough to warrant the rejection of externalism anyhow. I will also briefly explore the consequences of my defense of externalism with respect to the debate over the compatibility of externalism and introspective self-knowledge