  Before examining how Descartes might defend himself, it is important to note that the question at issue is typically framed in non-Cartesian terms and thus often misses its target. Both Kant and Russell for example are interested in the logical issue of whether existence is a predicate. Descartes, in contrast, was not a logician and disparaged the standard subject-predicate logic inherited from Aristotle. Although, as discussed above, he sometimes presents formal versions of the ontological arguments as heuristic devices, Descartes thought that God’s existence is ultimately known through intuition. This intuitive process is psychological in character. It is not a matter of assigning predicates to subjects but of determining whether the idea of a supremely perfect being can be clearly and distinctly perceived while excluding necessary existence from it through a purely intellectual operation. To be sure, Descartes was interested in the ontological question of whether existence is a “property” of substances. For him, however, the analogues of properties are clear and distinct ideas and ways of regarding them, not predicates.