What did Descartes do once he was sure of his assertion I am thinking, therefore I exist?
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Descartes asked himself what kind of thing he was and concluded that he was a thinking thing, that is, a mind-soul, and not the author of his own being, who must be God. God created both Descartes as an immaterial thinking thing, or soul, and the physical universe that included Descartes’ body. There was a second proof for God’s existence in Descartes’ ontological argument: God was all powerful and all good, existence was better than nonexistence, therefore God existed.
Because God was good, he could not be a deceiver, and the earlier doubts about the existence of the external world, and the validity of logic and reason, were put to rest. The doubts about sense data could always be corrected by further sense experience. And the distinction between being awake and being asleep could be solved after one was awake and compared the two states. God had made mankind such that our perceptions of the reality of a world that existed could be trusted.