[S]ince I am a thinking thing, and have in me an idea of God, whatever finally the cause may be to which my nature is attributed, it must necessarily be admitted that the cause must equally be a thinking thing, and possess within it the idea of all the perfections that I attribute to the divine nature.
The trademark argument can be analyzed (or rationally reconstructed) as follows:
1. I have an idea of God.
2. Everything which exists has a cause.
3. Therefore, there is a cause of my idea of God.
3. There is a cause of my idea of God.
4. The cause of an effect must contain at least as much reality as the effect.
5. Therefore, the cause of my idea of God must contain at least as much reality as my idea of God.
5. The cause of my idea of God must contain at least as much reality as my idea of God.
6. The idea of God contains perfection.
7. Therefore, the cause of my idea of God must contain perfection.
7. The cause of my idea of God must contain perfection.
8. No being which is not God contains perfection.
9. God is the cause of my idea.
9. The cause of my idea of God is God.
10. If something is the cause of something else, that something exists.
11. Therefore, God exists.
The CAP compares the cause of ideas to the cause of objects, but, whereas objects often have straightforward causes, ideas do not.
The idea of God contains only the idea of perfection, not perfection itself.
Gaunilo - I may have the concept of a perfect island. The perfection of this island would imply that it would exist, however this is not the case. A concept of something does not make it exist by adding the attribute of perfection.
David Hume – The idea of God could be arrived at by considering qualities within oneself (wisdom, strength, goodness) and magnifying them.
Descartes states that for the idea of the trademark argument to work, we must have a clear and distinct idea of God, i.e. a personal, infinite, monotheistic God. Descartes states that everyone is born with some kind of concept of God, no matter how broad it is. If we reach another idea of god, other than the traditional monotheistic one, Descartes would argue that the idea of God we have reached is not the idea of the clear and distinct God that we are looking for - however, he says that by looking closer we can show people that the idea of the god that they have been thinking of is actually, underneath, really the idea of God. However, if it is necessary to show people where they have reasoned wrongly, then the idea of God is not innate, as they have not reached it of their own accord.
The idea a man has of perfection is itself imperfect. If one were to ask a man to describe perfection, it is impossible that his description could be accurate. If man's idea of perfection came from a perfect God, it would follow that his idea of perfection itself be perfect. Since the idea of perfection is imperfect, it is more reasonable to assume that it might have come from other imperfect sources.