Modalities in Medieval Logic

This dissertation is an exercise in conceptual archeology. Using the tools of contemporary logic we analyse texts in medieval logic and reconstruct their logical theories by creating a formal framework which models them. Our focus is medieval texts which deal with various modalities: the writings on alethic modalities by William of Sherwood, Pseudo-Aquinas, and St. Thomas Aquinas in the 13th century, St. Anselm of Canterbury’s writings on facere and debere in the late 11th century; Lambert of Lagny’s 13th-century treatise of supposition and its connection to modern temporal logic; Roger Swyneshed’s dynamic modality of self-falsification, written in the early 14th century; and the different modes of being which are expressed in statements about the Trinity, from an anonymous, late-period text. We supplement our discussion of these medieval texts with a historical chapter discussing the relationship between the church and the development of modal and temporal logic in the 13th and 14th centuries, and two appendices containing translations into English of various source texts. We demonstrate that by using logical tools which have been introduced in the last quarter-century we can make better sense of the theories of medieval logic, particularly medieval modal logic, than we could 50 or 75 years earlier, when the logician’s primary tool was the mathematical logic of Frege and Russell. The venture is also fruitful in the other direction: We point to places where medieval responses to certain philosophical or theological problems seems more apropos than favored modern responses * * * mentions Duhem