Descartes' "trademark" Proof of God's Existence (27-Nov-2003)

Reading : Western Philosophy V.3 "God and the Idea of Perfection"

Having reasoned his way into the position of being able to believe in nothing other than his own existence, Descartes requires something else in order to be able to bootstrap his metaphysical picture. That something is God: given that God exists and that He is incapable of deception, Descartes is able to be certain of things outside himself. But how can we be sure that God exists? Descartes has two proofs: a version of the ontological argument, and the "trademark" proof.

In this second formulation, Descartes first uses the "causal reality principle": for an effect to occur, it must have a cause, and that cause must be at least, if not more, perfect than the effect it produces. In the physical world, we might use the term "entropy", or perhaps "conservation of momentum" to describe the same phenomena: for example, the effect of my throwing a stone is that the stone is imparted with a certain amount of energy, which will be no greater (and probably less) that the energy I expended in moving my arm. In building a bridge, all I am doing is rearranging bits of stuff that were there before.

Descartes extrapolates from this to affirm that our knowledge and beliefs are no different: "for if we suppose that an idea contains something which was not in its cause, it must have got this from nothing; yet the mode of being by which a thing exists...is certainly not nothing, and so it cannot come from nothing".

Since one of the ideas I have in my mind is of a perfect God, where can that have come from? The idea of perfection must have come from something which is more real than the idea itself, and the only thing that could be is God, therefore God exists. "It only remains for me to examine how I received this idea from God. For I did not acquire it from the senses; it has never come to me unexpectedly, as usually happens with the ideas of things that are perceivavle by the senses, when these things present themselves to the external sense organs - or seem to do so....the only remaining alternative is that it is innate in me, just as the idea of myself is innate in me". Descartes likens the idea of god to the "mark of a craftsman stamped on his work".

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