The Unity of the Soul and Contrary Appetites in Medieval Philosophy

Abstract

The history of the so-called Achilles arguments in the Middle Ages is largely unwritten. In his otherwise informative work, Mijuskovic only deals with the Middle Ages in one page and he is then mostly concerned with Thomas Aquinas.1 Although quite a lot has been published lately on medieval conceptions of the soul, not much attention has been given to these arguments. In this article, I will try to amend this to some extent, although a proper treatment requires a whole monograph. Following the terminology developed in the introduction to this book, I will deal with the broad and the narrow Achilles arguments, and I will trace these in the works of Augustine, Avicenna, Thomas Aquinas, John Peter Olivi, William Ockham and John Buridan. It will become apparent from my discussion of these authors that no Christian medieval thinker, except perhaps Olivi, accepts the broad Achilles argument. Their reason for not accepting it seems to be that they think it proves too much and ultimately puts limits on God’s omnipotence. Most of them will accept the narrow argument, however. A medieval thinker that accepts both arguments explicitly is Avicenna, and his outline of the two arguments becomes the main source for later medieval thinkers’ knowledge of them. After Aquinas and Olivi the notion of the simplicity and unity of the soul becomes a commonplace repeated by most medieval thinkers in one way or another, but with Ockham a new twist to the argument can be observed. He uses the notion of the soul’s simplicity as a premise in a paradox. Together with the notion of inner emotional conflicts and the principle that no contraries can exist in the same subject at the same time, the soul’s simplicity forms a dilemma that many subsequent thinkers had to comment on. Buridan, as will be seen, formulates a very influential