Beatriz Laporta

This dissertation investigates how Descartes created space in his philosophy for the uncertain and confused knowledge, through the consideration of the substantial union between soul and body. In the metaphor of the "tree of knowledge", as presented in the Preface to his Principles of Philosophy, the roots are metaphysics, the trunk is physics, and the branches are mechanics, medicine and morality. We aim to demonstrate that the metaphysical "roots" and the physical "trunk" are the fundament of the practical issue of morality, of the plan of the knowledge of experience and feeling, that is, of uncertain and confused knowledge. The study of his letters to Elisabeth from 1643 casts new light on how this practical question is conceived, insofar as Descartes addresses how it is possible for the soul to move the body. We intend to discuss why Descartes suggests that Elisabeth should think of the soul as having extension in order to understand how it has force to move the body, dealing with a question that has no rational answer. It is our thesis that the theorization of the distinction between substances enables Descartes' proposition of a new physics, distinct from the Aristotelian-Thomistic physics of substantial forms, and, especially, that the substantial union is what allows this physics, applied to human being, to be a physiology of the proper body, that is, non-hypothetical.