Introduction
Our bodies cannot account for our being the same thing over time because even though human beings grow from babies to adults over the course of their lifetime, the identity of the body over time is secured by its continuing union with a self-same soul. Descartes states, “Provided that a body is united with the same rational soul, we always take it as the body of the same man. Whatever matter it may be and whatever quantity or shape it may have.”
Substance Dualism
Descartes proposes to solve the problem of identity with his substance dualism by arguing that essentially, each being is a distinct thinking substance. The substance does not change over time simply because our bodies have changed. “I” implies the thinking substance that goes through mental changes and modifications but does not lead to the thinker having the thoughts and perceptions change.
Conway’s vs Descartes Accounts
Conway’s account of an “essential substance” or “soul” argues that creatures can change radically. Each being is an idea put forward by God into a creature, which results in each being being an essential soul. The soul achieves individuation from a pre-creation idea. Conway further portrays the soul of a man as not a single indivisible thing. Conway states “… This, every human being indeed, every creature whatsoever, contains many spirits and bodies.” For this reason, a man who lives a moral life on earth may become an angel and a brutish man on earth will turn into a beast.
Conclusion
On the other hand, Descartes’s account of human beings as, fundamentally thinking substances argues that our bodies change over time. However, this does not mean that we as distinct thinking substances essentially change over time.