Substance Dualism and Its Arguments

Among other things, Renee Descartes was an influential philosopher during the enlightenment era. This era, which is characterized by what, at the time, was controversial thinking is exactly what Descartes was known for. His "out of the box" thinking not only raised eyebrows, but it also brought a lot to the table. One of his most discussed ideas was that of substance dualism. In this theory, Descartes describes the mind an body as two separate substances. But to completely understand exactly what Descartes means by this, one of his other, more renowned theories must be explained first.

One of Descartes' first ideas was the material is in constant motion, and that all motion is my contact. With this he explains that colors, sounds, smells, etc. are results of impressions produced by the action that the specific material has on our organs. So, to explain how we hear, Descartes says that sound is a result of noise physically hitting and making an impression upon our ears.

But, all of these sensory responses are purely physical. So, another explanation was needed in order to describe that which in not physical such as thoughts, emotion, pleasure, and pain. And the result of this was Descartes' substance dualism theory. Because things such as pleasure, pain, thoughts, and emotion do not occur physically, but rather in the mind, his conclusion was that they are two separate things. His main reasoning for this is clearly stated when he says "I saw that while I could pretend that I had no body and that there was no world and no place for me to be in, I could not for all that pretend that I did not exist. I saw on the contrary that from the mere face that I thought of doubting the truth of other things, it followed quite evidently and certainly that I existed..." (Stevenson 86). In this, he explains that it was possible for him to doubt the existence of his body, without doubting his own existence as a thinking being. Therefore his existence as a thinking being must be separate from his bodily existence; his mind must be distinct from his body.

Descartes elaborates on what exactly his body and mind are. His body, he argues, extends into space, is divisible and obeys the laws of physical science. His mind, on the other hand, is incorporeal. It does not extend into space and does not obey the laws of physical science. But though these two realms, as he calls them, are not the same, they can interact. Material things can produce mental effects. So, even though the mind and body are two separate things, they are intertwined.

Descartes gives two main arguments for the conclusion that mind and body are separate. These arguments are based upon language and rationality, comparing animals and humans. Animals, Descartes argues, can be compared to machines. This goes back to Descartes previous theory of the constant movement of material. Because humans can form ideas from preserved experiences with material things, we have something that animals do not. According to him, animals do not have the sophistication or reason to do this. This also means that animals "... could never use words, or put together other signs, as we do in order to declare our thoughts to others... it is not conceivable that such a machine should produce different arrangements of words so as to give an appropriately meaningful answer..." (88). Although the animal may be able to "utter words", it cannot string those words together and give them any real meaning. They are mimics due to the fact that animals lack of reason.

His second argument is that an animal's actions are strictly that. He says "...even though the such machines might do some things as well as we do them, or perhaps even better, they would inevitably fail in others..." (88). He goes on to explain that the reasoning behind this is because the animal's actions are not through understanding, but because it is their nature to do so. Descartes says that animals act upon their bodily functions and their basic survival needs are what drive them. And, again, the lack of sophistication and reason are at the root of it.

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