This monograph articulates and defends a theory-based epistemology of modality (TEM). According to TEM, someone justifiably believe an interesting modal claim if and only if (a) she justifiably believes a theory according to which that claim is true, (b) she believes that claim on the basis of that theory, and (c) she has no defeaters for her belief in that claim. The book has two parts. In the first, the author motivates TEM, sets out the view...