A discussion of Lloyd’s Tarner Lectures at Trinity College. The importance of Lloyd’s previous scholarship is characterized and these sweeping, erudite lectures are placed in the context of that scholarship. In the broadest terms, the lectures are a call to culturally and historically comparative study of human reasoning. At their heart is a comparative history of scientific theorizing from the ancients through to modern science. Lloyd rejects the positivist picture, and the view of modern and ancient science as discontinuous; he urges scholars to undertake comparative work on the ancient sciences in different traditions. This critical notice evaluates Lloyd’s view and raises several questions for further reflection.