This is a dissertation on how certain cognitive limitations inform a theory of knowledge. Explanations in terms of the pure indexical "I" indicate a class of cognitive limitations. "I" cannot be completely eliminated from any successful explanation of how the world is intelligible to me and only I can refer to myself with the indexical "I." This raises the possibility that there are thoughts that I can think that cannot be thought by anyone else. Given what an epistemological theory must say about the definition, structure, and instances of knowledge and epistemic merit in general, such limits to cognitive access must arise both in its explanations of ordinary cases and its specialized theoretical concepts. The main contention of this dissertation is that it must be possible for an epistemological theory to plausibly account for these limitations.