Rene Descartes in his letter to Regius and his passage to Elizabeth is raising vital questions about what it means to be a human being. As he does so, he refers to a number of the major philosophical questions of the day, such as the mind-body problem, the existence and meaning of the soul, and the meaning of human thought. From these brief statements made by Descartes in these two letters, it is possible to synthesize a view of what makes a human being and of the nature of the human being in terms of the combination of mind, body, and soul, in the view of Descartes. This same issue is addressed by Douglas C. Long, whose comments on the matter can serve to extend the debate further, clarify some of the points and raise other issues and arguments.
Descartes began with the now well-known proposition, "I think, therefore I am," and from this he built a philosophical structure striving for a degree of mathematical certainty. In these two excerpts, though, he shows that the fact that he thinks does not explain the source of that thought, the meaning of being human, and the nature of the soul that human thought also presupposes. He begins in his letter to Regius by stating that the human being is made up of body and soul, and he sees these as existing in a true substantial union. The human being is thus not a body with a soul attached, but rather an entity consisting of a necessary body and soul. To lose one, then, is to be no longer human. For Descartes, death thus leads to a different state, a non-human state, a state of otherness. This question occupies Descartes greatly in this letter, and he analyzes what it means to be human, and what the mixture of mind and body may mean. Descartes has shaped part of his argument to serve his need of refuting those who believe that the soul is mortal while also satisfying theologians, and thus he makes clear that part of his argument would be different if he were essentially stating what ...