The essence of material things and the ontological argument

Meditation 2 demonstrated that I am essentially a thinking thing. In meditation 5 Descartes asks what the essential property of material things is. He claims it is extension (being in space) This is the one property that is most clearly grasped when we consider our ideas of material things.

The ontological argument I have an idea of a perfect being But a perfect being that did not exist would not be perfect Therefore, a perfect being exist. The argument claims that existence follows necessarily from the concept of a perfect being

Compare: A perfect being would have to all knowing (ignorance is an imperfection) And: A perfect being would have to exist (nonexistence is an imperfection)

Objection 1: The perfect island I have an idea of a perfect island If this island did not exist it would not be perfect. Therefore a perfect island exists. But this argument is silly. And it looks like it uses the same principle of reasoning as the ontological argument.

Objection 2: existence is not a predicate. For the argument to work, it must be possible for existence to be part of the concept of something, like “red” is part of the concept of my red chair. But is existence ever really part of a concept?

Compare: My chair is red My chair is broken My chair is not really red, but blue. These predicates seem to add something to the concept But does “My chair exists” add anything to the concept?