... that God existed - if one has an idea of God, it must follow that he exists. Descartes uses two arguments to prove this existence: the cosmological, and the ontological argument. The first states that an idea can only be explained in effect of its cause, or 'whence can the effect draw its reality if not from its cause?'1 Here, Descartes must show how he has the 'idea' of God in virtue of it being the effect of some cause. The reality of the idea of God must have a cause with 'as much reality as its effect'. Relying on the necessary principle that the lesser cannot give rise or creation to the greater, Descartes hopes to prove that to conceive of something far greater than himself, that idea must have been placed there by that greater thing. The idea cannot exist 'unless [it] had been put into me by some ...

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