This article considers the relationship between John Buridan’s natural philosophy and medicine. By examining some aspects of Buridan’s description of the human body related to sensation, nutrition, and generation—especially as they were framed in the so-called “controversy between philosophers and physicians”—this article shows that, though mostly faithful to Aristotelian doctrine, Buridan’s theoretical biology relies to a large extent on medical ideas.

Is a human being something that is one per se, or are humans composed of two independent substances? Treating the soul as the form of an organic body seems to offer one way of addressing the difficulty. But the debates about the nature of the soul which began to emerge in the 1270s made this question problematic. This article considers Buridan’s solution to the problem of how to unify what is corporeal and divisible on the one hand with what is incorporeal and indivisible on the other. Beginning with sensation, which concerns the unity of the sensitive soul and sense data, we turn to the act of thinking, where the intellective soul is united with the image or phantasm qua mover, leading to the realization that the unity of a human being is no longer self-evident. To solve the problem, Buridan takes up and transforms ways of thinking about the human soul inherited from older debates around Averroist psychology, such as the theory of two subjects and the conjunction of the sensible with the intelligible during cognitive activity.

In his commentary on Aristotle’s Physics, John Buridan (c. 1300–1361) presents his well-known rejection of final causality. The main problem he sees with it is that it requires the cause to exist before the effect. Despite this, he retains the terminology of ends. This has led to some difficulty interpreting Buridan’s view. In this article, I argue that one should not misunderstand Buridan’s terminology and think that he still retains some use or explanatory function for final causality in nature. To make this point, I look first at Buridan’s text, but then also at three thinkers who discuss Buridan’s view in detail: Albert of Saxony (d. 1390), Paul of Venice (d. 1429), and Luis Coronel (d. 1531). They all have a very clear idea of what Buridan’s view was and understand that it entails a rejection of final causality, but they also all preserve his distinctive terminology. Paul of Venice especially discusses and criticizes Buridan’s view in detail. Besides confirming my interpretation of the rejection of final causality, this study also shows that the view was extremely influential well into the sixteenth century and attributed to Buridan throughout two centuries.

What is an occurrent mental state? According to a common scholastic answer such a state is at least in part a quality of the mind. When I newly think about a machiatto, say, my mind acquires a new quality. However, according to a view discussed by John Buridan (who rejects it) and John of Mirecourt (who is condemned in 1347 for considering it “plausible”), an occurrent mental state is not even in part a quality. After sketching some of the history of this position, I will present two common arguments against it—the argument from change and the argument from agency. I will then turn to Mirecourt’s own position on the matter. Mirecourt, I show, in fact offers us two different theories about occurrent mental states. The first, which I call the conservation theory, accepts that mental states are in part qualities. However, a mental state is a quality together with an action on the side of the mind, namely, its conservation of a quality within itself. The second position, which I will call the pure-action theory, holds that an occurrent mental state is not even in part a quality; instead, it is an action the mind performs which is neither the production nor the conservation of a quality within itself. Mirecourt characterizes such pure actions as “modes” of the mind, and it is this position which is condemned in 1347. In the final section, I turn to an objection that both Buridan and Mirecourt raise against the pure-action theory: if accidental states of the mind are mere modes of the mind, then why not suppose that all accidents are mere modes of the subjects which they qualify?

Historian of science Edward Grant believed that, by counting and classifying the uses of theological terms in commentaries on some of Aristotle’s natural books, he could show that medieval natural philosophy had no theological agenda. But his broad-brush approach may not reveal differences in the way individual authors used theological terms. A census of such terms in the De anima commentaries of John Buridan and Nicole Oresme undertaken in this paper suggests that Buridan was more mindful of theological scrutiny of the Arts faculty than Oresme, perhaps because Buridan’s career began when the effects of the Condemnation of 1277 were more strongly felt than they were a generation later when Oresme began to teach.