Abstract

This paper explores the interaction between medicine and metaphysics in modern natural philosophy and especially in Descartes ' philosophy. I argue that Descartes ' hypothetical account of birthmarks in connection with his embryology provides an argumentative proof of the metaphysical necessity of a substantial union between mind and body, which however does not threaten his doctrine of the real distinction between these two substances. It would appear that his argument relies on a temporal conception of alethic modalities and provides a new answer to Henricus Regius who in 1641 claimed that, for Descartes, the human being is an ens per accidens.