Summa Logicae

Summa Logicae is a monumental work on logic by the medieval philosopher and logician William of Ockham (c. 1287–1347), a leading nominalist. It is generally believed to have been written between 1323 and 1326, was first printed in Latin in Paris in 1488, and was subsequently reprinted in Venice, Oxford, and elsewhere. The work is divided into three parts: the first discusses the properties of terms, the second discusses propositions, and the third discusses arguments (syllogisms, demonstrations, consequences, and insoluble propositions, etc.). The Commercial Press Chinese edition, translated by Wang Lu, selects only about half of the full work, concentrating on its two most central parts: the theory of terms and the theory of propositions. The first part, "Theory of Terms," comprising more than seventy sections, moves from terms in general, the signification of terms, categorematic and syncategorematic terms, to genus, species, differentia, property, accident, definition, and description, then to a category-by-category discussion of the ten categories, and finally arrives at Ockham's most signature theory of supposition (material, simple, and personal supposition and their rules of division). The second part, "Propositions," systematically discusses the truth conditions of non-modal and modal propositions, various complex propositions (reduplicative, exclusive, exceptive, and those containing "begins" and "ceases"), as well as conversion and hypothetical propositions. The book is a key text for understanding late medieval semantics and logic, and the technical foundation for studying Ockham's nominalist principle that "entities are not to be multiplied beyond necessity." The Chinese edition includes a translator's preface that explains the structure of the original, the translation of terminology, and the nature of the abridgement, helping readers grasp the whole while reading the selected portions.