The Ontological Argument of Rene Descartes

Existence of Things

Having proved the existence of God from his own existence, Descartes used the same truth as his starting point of his proof for the existence of the physical world, his body and other things. He still employed clarity and distinctiveness as his criteria of faith.

Descartes asked the question, "How is it clear and distinct that the physical world, my own body and other things exists?" In answer to the question, he says that it is clear and distinct to us when we change our positions and move about; activities that imply that we have bodies which are extended substances. We also receive sense impressions of sight, sound and touch frequently even against our wills and we know for certain that these impressions come from bodies external to us.

This clear and distinct conviction that these impressions are made on one from corporeal objects must come from God. This is so because the corporeal objects exist in reality and they must be put there not by us but God himself. If it were not so, then God would be a deceiver who makes us believe what is not real. But these corporeal objects exist and impress us, therefore, God is not a deceiver. Thus, for Descartes, to know God, we must know the self, and to know the external world, we must know both self and God.

We can then summarily say that so far, Descartes has through his methodic doubt proved that the self, things and God exists. He has concluded that there are thinking things and that things that are extended have dimensions.