In this paper I present a new approach to the so called ars obligatoria of the thirteenth and early fourteenth century. In standard medieval disputations an opponent attacks a thesis defended by the respondent. Some thirteenth-century authors distinguish two duties that the respondent has. First, he must grant whatever seems to be true. Second, he must grant whatever follows from what he has already granted. When the first duty is overridden by the specific duty to defend a false thesis (which (...) is the main requirement of ars obligatoria), the second duty becomes the logical duty of keeping the set of one's answers consistent. A natural result of this model is the development of a concept of possibility based on the syntactic concept of formally correct inference, and not on any semantic considerations. (shrink)

The struggle to delineate the relationship between theology and logic flourished in the thirteenth century and culminated in two condemnations in early 1277, one in Paris and the other in Oxford. To see how much and what kind of effect ecclesiastical actions such as condemnations and prohibitions to teach had on the development of logic in the Middle Ages, we investigate the events leading up to the 1277 actions, the condemned propositions, and the parts of these condemnations connected to modal (...) and temporal logic specifically. We show that because of the specific motivations late thirteenth-century and fourteenth-century logicians had when working in modal and temporal logic, the effect of the 1277 condemnations on the development of those branches was much smaller than might have been supposed. (shrink)