Abstract

In this chapter, I investigate the metaphysical assumptions that medieval thinkers considered necessary in order to integrate the vegetative powers and processes into their conception of human beings as composed of a material body and an immaterial soul. My aim is to show that vegetative powers and processes are central to the late medieval debate on faculty psychology and on the unity or plurality of substantial forms. The chapter has two parts. First, I present three different accounts of the ontological status of the vegetative powers in relation to the body and the soul, as found in Thomas Aquinas, William of Ockham, and John Buridan. All three maintain that the vegetative powers belong to the soul but disagree as to whether they are identical with it or somehow distinct from it, especially when the soul in question is immaterial. Second, I investigate how medieval thinkers accounted for the metaphysics behind the operations of the vegetative powers in human beings, who are endowed with immaterial souls, in particular when it comes to procreation and digestion. A pressing problem for the vegetative powers of human beings is how they can produce a new substance when this composite is supposed to include an immaterial soul which is not naturally generated. Regarding procreation, one can distinguish two different approaches: dispositional generation of material conditions and substantial generation of the body. A similar problem for human beings arises in nutrition and growth once this process is taken to be some kind of substantial change, namely, the corruption of food and the production of new parts of the living being. Two accounts can be distinguished: “transmateriation” of the matter of food into the nourished body and generation of parts of the body.