(Ph.D., Stanford University). He works mainly in epistemology, philosophical logic, and the intersection thereof. His interests in epistemology include epistemic closure, fallibilism, skepticism, and contextualism, as well as epistemic paradoxes. In philosophical logic, his interests include applications of epistemic logic in epistemology, formal representations of knowledge change, and general modal logic. Recently he has been thinking about the relations between probabilistic and qualitative models for epistemic attitudes and modalities.