Questions such as; are my senses trust-worthy? What is my essential nature? All pertain to the major question of what constitutes as substance? This issue is the first fundamental conflict between the three philosophers. As Descartes was the first to touch on this problem, I will deal with him primarily. Descartes method of doubt, found in Meditations, was to doubt everything. He did not trust his senses, as they were prone to mistakes. He presented the idea that, as dreams can be so clear and vivid he doubted we could know whether we are dreaming or not. He also stated that we could not know whether our whole concept of reality was real as it could be fabricated by an evil demon. Then, it seems, everything must remain in doubt, not so for Descartes. He found that there is one thing that you can never be deceived on and that is; ‘you cannot doubt that you are doubting.’ You cannot be deceived that you are conscious or not as the very act of thinking you are conscious, is a conscious act. ‘Cogito Ergo Sum.’ I think therefore I am. Thus the mind becomes a core substance for Descartes.
Yet in dealing with what our essential nature is; mind is not the only substance that Descartes believes there is. The body is also a necessary part of substance. The essence of the body is to have extension but it is not in our nature to have a body as we can conceive of not having a body. Due to an intuition of the mind is the reason we know that physical stuff exits. Descartes unfortunately encounters a problem with dualism, that Leibniz singled out, which is the problem of casual interaction. If the mind and body are completely different kinds of substance how can they interact?
While Descartes believes that there are only two substances that can be trusted, mind and body, Spinoza believes that we are all part of the same substance and mind and body are one. Being against dualism, due to it not being a progressive line of thought, Spinoza considers thought and extension as two attributes of the one substance. Attributes are the essential characteristics of Substance. Substance, to Spinoza, ‘is that which is in itself and is conceived through itself.’ Along side Spinoza’s concept of substance, which is highly abstract, is the principle of sufficient reason. This principle states that there is sufficient cause for everything, no exceptions granted. If anything exists, it is this substance. Thus entails that our world could not exist if everything depended on something or someone else to exist. Spinoza believed that there was one entity that was responsible for its own existence, God.
In stark contrast to Spinoza’s concept of one substance, is the notion that substance is infinite. Leibniz puts a different spin on substance, believing that the fundamental constitutes of reality must be absolutely minimal, even more so than atoms. Leibniz calls this substance, Monads. Monads have no shape, size or parts. We must begin to understand what a monad is by beginning from the idea of a complete concept. A substance/monad is that reality which the complete concept...