Throughout history, philosophers have grappled with questions of how we should live and why, of politics, of science, of language. This dictionary anatomizes the philosophical tradition and shows the thoughts, paradoxes, errors and breakthroughs that underline human speculation. The dictionary shows philosophers at their best and their worst, at their most perverse and their most elegant. Organized by philospher, and indexed by thought, concept and phrase, it enables readers to discover who said what, and what was said by whom. Over 300 philosophers are represented, from Aristotle to Zeno, ranging from Einstein and Aquinas to Sartre and De Beauvoir, and the quotations range from short cryptic phrases to longer statements. This was the literary project on which A.J. Ayer was engaged at the time of his death in 1989. A large number of his professional colleagues had been enlisted by Professor Ayer to offer the quotations they felt needed to be included. Following his plan for the work, the project has been completed by Jane O'Grady.