Meditation III: Overall Summary
This meditation begins with a summary of Descartes’s conclusions so far. However, he finds that he cannot achieve a firm basis for certainty without first proving whether or not God exists, and if so, whether or not God is a deceiver.
To do this Descartes concentrates on where thoughts come from, classifying them according to whether:
they originate from outside himself (adventitious ideas),
are created by himself (factitious ideas),
or that he is born with them (innate ideas).
The purpose of this is, ultimately, to prove that the idea of God is present in his mind as an innate idea.
Finally, having proved this, Descartes uses what has come to be called the trademark argument, attempting to show that the presence of the idea of God in his mind is equivalent to the trademark (or signature) left on an object created by a craftsman.