Abstract

All Aristotelians subscribed to the thesis that the soul as the principle of life has many powers. But how are the powers related to the soul’s essence? It has often been argued that medieval philosophers gave two answers to this ques- tion: some took them to be necessary accidents that are distinct from the soul’s essence, whereas others simply identified them with the essence. This paper intends to show that there were alternatives to these two standard models. Peter of John Olivi argued that the powers are not accidents but substantial forms that constitute the soul’s essence. He thereby defended a strong mereological thesis, for he assumed that the powers are literally parts that make together a whole. Henry of Ghent also rejected the idea that powers are accidents. Instead, he defended the claim that a power of the soul is a whole constituted by the soul’s essence and a relation determining the essence to an act and an object. In making this claim, Henry proposed a determination thesis. The paper dis- cusses both theses in detail, looks at the arguments Olivi and Henry adduced against the two standard models, and evaluates their theories in the historical context.