  In the Fifth Meditation and elsewhere Descartes says that God’s existence follows from the fact that existence is contained in the “true and immutable essence, nature, or form” of a supremely perfect being, just as it follows from the essence of a triangle that its angles equal two right angles. This way of putting the a priori argument has puzzled commentators and has led to a lively debate about the ontological status of Cartesian essences and the objects which are purported to “have” them. Some commentators have thought that Descartes is committed to a species of Platonic realism.  According to this view, some objects that fall short of actual existence nevertheless subsist as abstract, logical entities outside the mind and beyond the physical world (Kenny, 1968; Wilson, 1978).  Another commentator places Cartesian essences in God (Schmaltz 1991), while two recent revisionist interpretations (Chappell, 1997; Nolan, 1997) read Descartes as a conceptualist who takes essences to be ideas in human minds.