Q&A for Western Philosophy

 How does Descartes prove the existence of ‘self’, ‘God’ & ‘external world’?

Descartes did not believe that the information we receive through our senses is necessarily accurate. He started to doubt everything, including the foundational or basic premises, achieved through sense perceptions. He concluded that only the mathematical certainty is the true certainty. Therefore, he adopted the tool of reason. He believed only through the use of pure reason, we can achieve true knowledge. Therefore, he introduced „method of doubt‟. He comes to the conclusion of saying „I think, therefore I exist‟. In this he concludes, for him to be deceived in this conclusion also requires thinking. To be thinking is a ground for a truth that is absolutely certain and immune from doubt because thinking logically entails existence. With the sure knowledge that he exists and without relying on the sensory perceptions, he proceeds to investigate his existence.

He came up with „theory of Ideas‟. Ideas can be said to have objective reality. He believed in the law of causality that something has to be the cause for something to exist. He also stated, causes must have the as much reality as the effect. Cause should have the minimum of the equal effect. There is an image of God that exists within mankind. There has to be a perfect being existing objectively from whom his innate idea of a perfect being derives wherein he could have created the ideas of all substances, but not the one of God. The second argument is that of, since he is an imperfect being, he cannot be the maker of himself nor his parents. This leaves only a perfect being, God who would have had to exist to create.

Since God being all good, and not a deceiver, we can rely on our God-given senses when properly used. Through his senses, he is clearly able to perceive the material world, and since God can do anything that is logically possible, God could have created the material world. This gives the foundation for proving the existence of the external world. He gives 2 reasons that his ideas of material things are not produced by an unknown faculty of his mind, as it produces dreams. The active faculty required for causing ideas has no intellection, and the ideas occur independently of will. Therefore, whatever that causes the ideas in his mind cannot be in him but outside of him. It is now for certain that he knows two things – a fuller knowledge of God & a better understanding of self. Here he introduces his proof that his entire essence is contained in a being as thinking thing. He argues, the idea of material things cannot be caused by God or any external substance other than the material things since God is not the cause of the ideas of material world, lest he be a deceiver, but since God is not a deceiver, the idea of the material things must come from the material world itself. This proves there is an external world apart from him.