The Summa Logicae ("Sum of Logic") is a textbook on logic by William of Ockham. It was written around 1323. Systematically, it resembles other works of medieval logic, organised under the basic headings of the Aristotelian Predicables, Categories, terms, propositions, and syllogisms. These headings, though often given in a different order, represent the basic arrangement of scholastic works on logic. This work is important in that it contains the main account of Ockham's nominalism, a position related to the problem of universals. Source: Wikipedia (en)