Descartes proposed that there are three types of ideas: Innate, Fictitious, and Adventitious. Innate ideas are and have always been within us, fictitious or invented ideas come from our imagination, and Adventitious ideas come from experiences of the world. He argues that the idea of God is Innate and placed in us by God, and he rejected the possibility that the idea of God is Invented or Adventitious.

Argument 1

Something cannot come from nothing.
The cause of an idea must have at least as much formal reality as the idea has objective reality.
I have in me an idea of God. This idea has infinite objective reality.
I cannot be the cause of this idea, since I am not an infinite and perfect being. I don't have enough formal reality. Only an infinite and perfect being could cause such an idea.
So God — a being with infinite formal reality — must exist (and be the source of my idea of God).
An absolutely perfect being is a good, benevolent being.
So God is benevolent...
So God would not deceive me, and would not permit me to err without giving me a way to correct my errors.
Argument 2

I exist.
My existence must have a cause.
The only possible ultimate causes are
a) myself
b) my always having existed
c) my parents
d) something less perfect than God
e) God
4. Not a. If I had created myself, I would have made myself perfect.
5. Not b. This does not solve the problem. If I am a dependent being, I need to be continually sustained by another.
6. Not c. This