Thomas Aquinas, Henry of Ghent, and John Duns Scotus on the Causation of Proper and Inseparable Accidents

Medieval philosophers such as Henry of Ghent and John Duns Scotus defended the possibility of what I call self-agency, the view that substances bring about in themselves their own necessary and inseparable features. In this paper, I propose that self-agency should be understood as an attempt to clarify the relationship between what is necessary but still accidental, and what is essential. I explore this view in the context of two objections against the possibility of self-agency: a general one, according to which the relationship between what is essential and what is necessary (but accidental) should not be envisaged in causal terms; and a more specific one, namely, that there is no need to consider this relationship to be a case of efficient causation. Against the first objection, I show that in the thirteenth century medieval philosophers envisaged this relationship in causal terms because of the way they conceived the ontological status of accidents. Against the second objection, I show that while Henry admits the possibility of self-agency as a consequence of his view of the nature of causal powers, Scotus thinks that without self-agency one cannot account for why proper and inseparable accidents are necessarily related to their subject of inherence.