Descartes’ most famous statement is Cogito ergo sum,” I think, therefore I exist.” With this argument, he proposes that the very act of thinking offers a proof of individual human existence. Because thoughts must have a source, there must be an “I” that exists to do the thinking.
In arguments that follow from this premise, he points out that although he can be sure of nothing else about the existence he can’t prove beyond a doubt that he has hands or hair or a body, he is certain that he has thoughts and the ability to use reason. He asserts that these facts come to him as “clear and distinct perceptions”. He argues that anything that can be observed through clear and distinct perceptions is part of the essence of what is observed. Thought and reason, because they are clearly perceived, must be the essence of humanity.
Consequently, he says that a human would still be a human without hands or a face. He also says that other things that are not human may have hair, hands, or faces but a human would not be a human without reason, and only humans possess the ability to reason. He firmly believed that true knowledge can be directly gleaned not from books but only through the methodical application of reason. Because he believed that every human possesses the ‘natural light’ of reason, he believed that if presented all his arguments as logical trains of thought, then anyone could understand them and nobody could help but be swayed.
The first thing to observe is that Kant explicitly says that reason is the arbiter of truth in all judgments. He says that it is necessary for the law of reason to seek unity, since without it we would have no reason, and without that, no coherent use of the understanding, and lacking that, no sufficient mark of empirical truth.”
His earliest statement of the Principle of Sufficient Reason (PSR) appears in his first published work, the 1663 geometrical exposition of Descartes’ principles of philosophy. The book states ‘Nothing exists of which it cannot be asked, what is the cause or reason/ why it exists.
Since existing is something positive, we cannot say that it has nothing as its cause, therefore we must assign some positive cause, or reason, why a thing exists, either an external me that is me outside the thing itself, or an internal one, me comprehended in the nature and definition of the existing thing itself.
Spinoza’s insistence that even the non- existence of things can be explainable is crucial. It allows him, for example, to argue that were God not to exist, his non- existence must be explainable. Since God is a substance, he argues his existence or non- existence cannot be caused or explained externally. Hence, were God not to exist, he would have to be the cause of his non- existence, just as a square, circle is the cause of its non- existence. But since God is not a contradictory entity, He cannot internally rule His own existence, and hence He must exist.
If there were two indiscernible individuals, then God would have acted for no reason to treat them differently. But there is a reason for everything. So, there are no indiscernible yet numerically distinct things.
He who says there is no need of reason has a reason behind it.
· Copleston, Fredrick. “A History of Philosophy.” Modern philosophy, Vol 4, Descartes to Leibnez, New York : Doubelday and Company, Inc., 1960.
· “Descartes” www.stanfordedu.stanford university. 14 Feb 2015.
· Gilson, Etienne and Langan, Thomas. “A History of Philosophy.” Descartes toKant, New York: The colonial press Inc., 1963.
· “Kant” www.stanfordedu.stanford university. 10 Sep, 2008.
· Spinoza, Benedict. “The Collected works of Spinoza.” Vol. I, Translated and edited by Edwin Curley, Princeton: Princeton University Press, 1985.