Galen of Pergamum (AD 129-c.216) was the most influential doctor of later antiquity, whose work was to influence medical theory and practice for more than fifteen hundred years. He was a prolific writer on anatomy, physiology, diagnosis and prognosis, pulse-doctrine, pharmacology, therapeutics, and the theory of medicine; but he also wrote extensively on philosophical topics, making original contributions to logic and the philosophy of science, and outlining a scientific epistemology which married a deep respect for empirical adequacy with a commitment to rigorous rational exposition and...