Mediaeval logicians often wrote about changes between contradictory states, for example a switch’s changing from being on to not being on. One of the questions discussed in these writings was whether at the moment the change occurs the changing thing is in the earlier or the later state. The present paper investigates the general setting for that question, and discusses the answer given by Walter Burley, an important early-fourteenth century author whose theory was a standard one. Burley’s theory at first (...) seems arbitrary, and moreover committed to serious theoretical problems. The last part of the paper therefore considers what unspoken factors may have motivated Burley. Certain causal principles are suggested that would remove the apparent arbitrariness and avoid the theoretical problems with his theory, but only at the expense of revising it in a substantive way. (shrink)

Ockham’s approach to the problem of the instant of change as it is found in the Summa logicae i, chapter 5, and ii, chapter 19, is usually described as “purely logical,” narrowing the treatment of “begins” and “ceases” to simplistic cases. The aim of this paper is to complement our knowledge of Ockham’s position on the problem of the instant of change by analysing the treatment of the problem he gives in his questions on the Physics 98-101. In these passages, (...) Ockham adopts a “physical approach” in order to deal with problems related to the continuity of alteration and the production of the form of the mix from elementary qualities. To solve these problems, he is compelled to give up one of the most important claims at the basis of the logical approach that he adopted in the Summa logicae, namely that the distinction between permanent and successive entities is not relevant in the assignment of truth-conditions to propositions containing the aspectual verbs “beginning” and “ceasing.”. (shrink)