But how could one know that the true and immutable nature of a being is to exist purely on the basis of an idea? In fact, this argument works better for a triangle, since its essence is implied in the definition. It does not hold, however, for God, whose definition is contestable. Descartes would resort to saying that any other concept of God would be self-contradictory. This is not necessarily true. One's definition of God's attributes does not make it the case.

Descartes recognizes the major objection to this position: that his thinking the idea of God does not make God exist. What a person thinks does not create the thing. He says, "For my thought does not impose any necessity on things; and just as I may imagine a winged horse even though no horse has wings, so I may be able to attach existence to God even though...
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