This dissertation makes progress on the mind-body problem by examining certain key features of epistemic defeasibility, introspection, peer disagreement, and philosophical methodology. In the standard thought experiments, dualism strikes many of us as true. And absent defeaters, we should believe what strikes us as true. In the first three chapters, I discuss a variety of proposed defeaters—undercutters, rebutters, and peer disagreement—for the seeming truth of dualism, arguing that not one is successful. In the fourth chapter, I develop and defend a novel argument from the indefeasibility of certain introspective beliefs for the conclusion that persons are not complex objects like brains or bodies. This argument reveals the non-mechanistic nature of introspection. / text