Medieval logicians advanced far beyond the logic of Aristotle, and this book shows how far that advance took them in two central areas. Broadie focuses upon the work of some of the great figures of the fourteenth century, including Walter Burley, William Ockham, John Buridan, Albert of Saxony, and Paul of Venice, and deals with their theories of truth conditions and validity conditions. He reveals how much of what seems characteristically twentieth-century logic was familiar long ago. Broadie has extensively revised his text for this second edition, while preserving the character of the first. There are now fuller accounts of supposition, of intentional contexts, and of medieval syllogistic, and the conclusion has been substantially expanded.