 Soto is regarded as responsible for the revival of Spanish-Thomistic logic, as distinct from both Renaissance-oriented logic, which used only ancient sources, and the extremely technical “sophistic” logic of Nominalism. His main sources were Aristotle, Thomas Aquinas and Petrus Hispanus’ Summulae logicales, from all of which, however, he deviated in many areas. In his Summulae, especially starting with the second edition of 1547, which became one of the most influential textbooks of this genre, he gives an introduction to traditional logic, including a theory of terms, propositions and conclusions (Soto 1529 [1980]). Whereas Petrus Hispanus had been criticized for serious inconsistencies, Soto gives his own interpretation, in an effort to build up a coherent doctrine. In the presentation of the different kinds of terms, he did not follow the Aristotelian categories, but instead presented the medieval distinctions between mental, written, and spoken terms, between categorematic and syncategorematic terms (that is, terms that have a meaning because they refer to things, concepts or other terms and those which only make sense within propositions as connections, but cannot be a subject or predicate, such as ‘if’, ‘all’, etc.), between absolute and connotative terms, and so on. He continued by presenting different kinds of proposition, including a version of supposition theory—the doctrine of the entities that the terms in a proposition, subject and predicate stand for (1529 [1980: 31–36]). Here Soto also discussed Nominalist and realist objections; but, in the end, he mostly defended the positions of Petrus Hispanus, largely omitting, however, complicated types of supposition such as distributive, confused, merely confused, etc., which had long puzzled medieval authors. The third book explains the different kinds of relation between propositions, including an extended version of the square of oppositions (1529 [1980: 72]), as well as truth conditions for modal propositions, conjunctions and disjunctions. In his discussion of the different kinds of valid and invalid conclusion, Soto not only referred to syllogisms (book 5) and the so-called insolubilia, or reflections on paradoxes (book 6), but also elements of the theory of consequentiae, a medieval type of logical conclusion that may go back to the Stoic logic of propositions (Read 1993; D’Ors 1983).