Some key arguments from Meditations III-V I. THIRD MEDITATION: The existence of God A. Cosmological proof of the Existence of God

A. Cosmological proof of the Existence of God In the 3rd Meditation, Descartes attempts to prove that God (i) exists, (ii) is the cause of the essence of the meditator (i.e. the author of his nature as a thinking thing), and (iii) the cause of the meditator’s existence (both as creator and conserver, i.e. the cause that keeps him in existence from one moment to the next). The proof that God exists premises that each of us understand the following clear and distinct idea of God: Definition. “By ‘God’ I mean the very being the idea of whom is within me, that is, the possessor of all the perfections which I cannot grasp, but can somehow reach in my thought, who is subject to no defects whatsoever.” Without entering into the details of the proof, Descartes’s objective is to demonstrate that this idea can have no other cause than God. Some of the main features of the proof are the following: —The proof is cosmological because it is an inference from a given effect (here the idea of God) to the existence of God as the cause of that effect, and proceeds by showing that every other possible cause is inadequate. It contrasts with the ontological proof of the Fifth Meditation in which Descartes argues from the essence of God, as a being possessed of all perfections, to the existence of God (on the ground that existence too must be accounted a perfection, i.e. inexistent beings are, by virtue of their lack of existence, less perfect than existing ones). —The aim of Descartes’s proofs are to demonstrate the irrationality of both atheism and agnosticism by showing that reason operating alone (independently of all the commitments of faith) requires us to affirm the existence of God with the very same certainty of which it revealed itself capable when affirming our own existence as thinking beings in the Second Meditation. —Accordingly, the proof presupposes nothing but (i) the meditator’s own existence as a thinking substance and (ii) the existence (as modifications of the meditator’s mind) of the ideas the meditator thinks. On the basis of these two certainties, together with the certainty of such eternal truths as that everything that exists must have a cause of its existence, Descartes reasoned that the existence in us of the idea of God is impossible through any other cause than God (to do so, he first excluded the possibility that any being less than God could be its cause, and then proved that the meditator is such a being, i.e. that the meditator cannot, unbeknownst to himor herself, be God). —If one accepts that Descartes’s reasoning in the proof is both valid (= the conclusion is known to be implied by the premises) and sound (= the premises are all known to be true), it enables one to know that God exists with the same skepticism-defeating certainty with which one knows that the idea of God exists as a present modification of one’s thinking being.