Roderick Firth's writings on epistemology amount to an exceptionally careful and cogent defense of an account of perceptual knowledge in the tradition Firth called 'radical empiricism.' This important book collects all of Firth's major works on epistemology; it also contains his only publication in ethics, the extremely influential essay on 'Ethical Absolutism and the Ideal Observer.' In addition, the book includes a number of important previously unpublished essays. Together, these writings constitute the most finished and compelling version of traditional empiricist epistemology. This book will be of value to students and scholars of epistemology, phenomenalism, and ethics.