John of Saint Thomas also known as John Poinsot (1589–1644), Portuguese theologian and philosopher. Born in Lisbon, he studied at Coimbra and Louvain, entered the Dominican order (1610), and taught at Alcalá de Henares, Piacenza, and Madrid. His most important works are the Cursus philosophicus (‘Course of Philosophy,’ 1632–36), a work on logic and natural philosophy; and the Cursus theologicus (‘Course of Theology,’ 1637–44), a commentary on Aquinas’s Summa theologiae. John considered himself a Thomist, but he modified Aquinas’s views in important ways. The ‘Ars Logica,’ the first part of the Cursus philosophicus, is the source of much subsequent Catholic teaching in logic. It is divided into two parts: the first deals with formal logic and presents a comprehensive theory of terms, propositions, and reasoning; the second discusses topics in material logic, such as predicables, categories, and demonstration. An important contribution in the first is a comprehensive theory of signs that has attracted considerable attention in the twentieth century among such philosophers as Maritain, Yves Simon, John Wild, and others. An important contribution in the second part is the division of knowledge according to physical, mathematical, and metaphysical degrees, which was later adopted by Maritain. John dealt with metaphysical problems in the second part of the Cursus philosophicus and in the Cursus theologicus. His views are modifications of Aquinas’s. For example, Aquinas held that the principle of individuation is matter designated by quantity; John interpreted this as matter radically determined by dimensions, where the dimensions are indeterminate. In contrast to other major figures of the Spanish Scholasticism of the times, John did not write much in political and legal theory. He considered ethics and political philosophy to be speculative rather than practical sciences, and adopted a form of probabilism. Moreover, when in doubt about a course of action, one may simply adopt any pertinent view proposed by a prudent moralist. See also AQUINAS, PEIRCE , SEMIOSI. J.J.E.G. John of Salisbury (c.1120–80), English prelate and humanist scholar. Between 1135 and 1141 he studied dialectic with Peter Abelard and theology with Gilbert of Poitiers in Paris. It is possible that during this time he also studied grammar, rhetoric, and part of the quadrivium with William of Conches at the Cathedral School of Chartres. After 1147 he was for a time a member of the Roman Curia, secretary to Theobald, archbishop of Canterbury, and friend of Thomas Becket. For his role in Becket’s canonization, Louis VII of France rewarded him with the bishopric of Chartres in 1176.
Although John was a dedicated student of philosophy, it would be misleading to call him a philosopher. In his letters, biographies of Anselm and Becket, and Memoirs of the Papal Court (1148– 52), he provides, in perhaps the best medieval imitation of classical Latin style, an account of some of the most important ideas, events, and personalities of his time. Neither these works nor his Polycraticus and Metalogicon, for which he is most celebrated, are systematic philosophical treatises. The Polycraticus is, however, considered one of the first medieval treatises to take up political theory in any extended way. In it John maintains that if a ruler does not legislate in accordance with natural moral law, legitimate resistance to him can include his assassination. In the Metalogicon, on the other hand, John discusses, in a humanist spirit, the benefits for a civilized world of philosophical training based on Aristotle’s logic. He also presents current views on the nature of universals, and, not surprisingly, endorses an Aristotelian view of them as neither extramental entities nor mere words, but mental concepts that nevertheless have a basis in reality insofar as they are the result of the mind’s abstracting from extramental entities what those entities have in common. G.S.