William of Ockham, the most prestigious philosopher of the fourteenth century, was a late Scholastic thinker who is regarded as the founder of Nominalism - the school of thought that denies that universals have any reality apart from the individual things signified by the universal or general term. Ockham's Summa Logicae was intended as a basic text in philosophy, but its originality and scope encompass his whole system of philosophy. Yet the paucity of English translations and the structural complexity have made the Summa, until now, almost completely inaccessible.