Paul Vincent Spade

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.

Let me begin then by introducing you to a distinction between what I will call a broadly “Platonic”-style and a broadly “Aristotelian”-style metaphysics. The guiding thread will be the notion of the essential and non-essential (accidental) features of a thing. Perhaps you will find what I am here calling an “Aristotelian” view unfamiliar and even foreign, because there is a kind of metaphysical “common denominator” in some philosophical circles today, left-over perhaps from the days of “analytic” philosophical insularity, but in any case quite unlike what I am here calling an “Aristotelian” metaphysics. Instead it is much closer to what I regard as a Platonic approach.

This paper defends the thesis that the mediaeval genre of logical treatises De obligatiombus contained a theoretical account of counterfacutal reasoning, perhaps the first such account in the history of philosophy. This interpretation helps to explain some of the theoretical disputes in the obligationes literature in the first half of the fourteenth century. Section 1 is introductory. Section 2 presents Walter Burley's theory, while section 3 argues for the counterfactual interpretation of obligationes and section 4 discusses difficulties with Burley's theory. Section 5 presents the textual basis for Richard Kilvington's theory, and section 6 outlines that theory. Section 7 discusses Roger Swyneshed's theory. Section 8 contains a summary and conclusion

In the summer of 1980, I was privileged to be on the teaching staff of the Summer Institute on Medieval Philosophy held at Cornell University under the direction of Norman Kretzmann and the auspices of the Council for Philosophical Studies and the National Endowment for the Humanities. While I was giving a series of lectures on supposition theory, I went to my office one morning, and there under the door some anonymous wag from the Institute had slid the pen and ink drawing you see in the graphic. It represents "Supposition" as a dragon, making a rude face at the viewer. The tail of the dragon is divided — not entirely accurately, as it turns out — into the various branches and subbranches of supposition. If the details are not altogether correct, the spirit is certainly understandable. I have absolutely no idea who the inspired artist was, but I have the original framed on the wall in my office.