Of Benson Mates’ many notable contributions to logic and the history of philosophy, one deserves special mention and emphasis – his pioneering and inspiring work on Stoicism. In 1948, when Mates completed his Berkeley PhD dissertation on Stoic logic, Stoicism was widely taken to be a dull successor to the exemplary work in philosophy generated by Plato and Aristotle. The Stoics were known to have devoted great attention to logic, but their logical theory was generally misperceived as an unoriginal and faulty version of Aristotelian logic. Following the lead of the eminent Polish logician Jan Lukasiewicz, Mates showed that Stoic logic differed fundamentally from Aristotelian logic. The latter is a logic of terms and categorical syllogisms, but in Stoicism logic is a theory of inferential relationships between variables that stand for propositions, as in: If the first, the second; The first; Therefore, the second (e.g. If it is day, it is light; It is day; Therefore it is light). As Mates presented it, Stoic logic proved to anticipate much of the modern predicate calculus. No less importantly, Mates showed that the Stoics developed a semantic theory that could be informatively compared with theories of Frege and Carnap.
He disseminated the work of his dissertation in his first book Stoic Logic, In its paperback edition (University of California Press, 1961), this book may justly be regarded as the moment when the Stoics began to recover their ancient reputation as significant and creative philosophers. Since then, many scholars have taken the study of Stoic logic further, and sophisticated work on all aspects of Stoicism proceeds apace. Credit for this admirable development belongs to Benson Mates. He will always be honored as one of the principal authors of the modern revival of Stoic philosophy.