This is the third volume of Jonathan Barnes' papers on ancient philosophy. It contains twenty-two pieces which turn about epistemological matters. The papers have all been brushed down, and some of them have been revised. One or two of them appear for the first time in English. The first three pieces form a prologue (and link this volume to its predecessor): they deal with certain ancient views about the relation between logic on the one hand and knowledge and science on the other. After that, the book divides into two unequal parts. The first part is concerned with proof, five of its ten chapters discussing Aristotle and three. The second is chiefly occupied with scepticism-more particularly, with the Pyrrhonian version of ancient scepticism. A final piece says something about the Book of Ecclesiastes. The essays in this volume, some of which are less familiar than others, are written with brio: anyone with an interest in ancient philosophy will find them amusing.