This book is a manuscript that was virtually complete when James W. Cornman died. Most of the chapters were in final form, and all but the last had been revised by the author. The last chapter was in handwritten form, and the concluding remarks were not finished. Swain took charge of the proofreading and John L. Thomas compiled the indices with the assistance of Lehrer. It is our opinion that this manuscript, like the other books Cornman published, is one of exceptional scholarly and philo sophical importance. As do all of his philosophical publications, this work reflects Cornman's great love for philosophy and his commitment to the search for truth. Every serious student and author of epistemology will benefit from and admire the thorough scholarship and rigorous argumentation they will find herein. It has been our privilege to partici pate in the preparation of the manuscript for the philosophical public. KEITH LEHRER MARSHALL SWAIN IX INTRODUCTION INTRODUCTION TO EPISTEMOLOGICAL SKEPTICISM Many philosophers try to refute skepticism, but few try to give a precise characterization of the thesis they attack. My first aim, consequently, is to characterize skepticism, or, more precisely, several species of skepticism. Then I shall choose those species I wish to consider and justify my choice. To begin, let me distinguish what I shall call "epistemological skepticism" from the thesis I shall call "ontological nihilism" and from what is believed by someone whom I shall call an "ontological skeptic".