This book examines skeptical problems originally raised by Descartes and Hume and currently discussed in philosophy of mind, philosophy of language, metaphysics, and epistemology. It answers the basic skeptical questions concerning the existence of what is now unperceived, the reality of what is perceived, and the existence of an external world. Johnstone shows how the recently proposed solutions to these skeptical problems-- pragmatic, coherentist, linguistic, and new-Kantian -- do not and cannot work, and how only a return to foundational investigation on the terrain of the radical skeptic is adequate to the task. His analyses make for a valuable summary of every significant argument brought against skepticism. In the course of his investigation, Johnstone probes a number of topical issues: knowledge, rationality, the nature of meaning, nonverbal thinking, the bodily nature of the thinking self, parasitism, the role of the tactile-kinesthetic body in feeling and belief, and the necessary role of free will in epistemology.