Yes, and here we are, once again Descartes invoked our notion of the perfect entity. When our reason perceives something clear and authentic as is the case with the mathematical properties of external reality it must be. Because a perfect God will not deceive us. Descartes claims that God guarantees that whatever we perceive by reason corresponds to reality. Frida Kahlo Salvador Dali Van Gogh starry night poster. All right, so he discovered he is a thinking being, God exists and there is a reality outside. Ah, but the external reality is very different from the reality of thought. Now Descartes asserts that there are two different forms of reality or the qualities.