Dualism is the philosophical belief that mind and matter are fundamentally distinct substances. William G. Lycan states that "according to Cartesian dualism, minds are purely spiritual and radically non-spatial, having neither size nor location" (Lycan, 47) and indeed, Descartes reached his conclusion by arguing that the mind and body are completely different in nature, making it possible for one to exist without the other. Whilst Descartes attempted to argue in favour of substance dualism, it can be said that his argument was ultimately weak, with substance monism being a far stronger viewpoint in the distinction between the mental and the physical. In this essay, I will attempt to argue that Descartes does not provide a convincing argument for the claim that mind and matter are distinct substances and instead, I will argue in favour of materialism through the particular exploration of functionalism.
In order to understand dualism, we must first come to terms with Leibniz's Law due to the fact that most dualist arguments rely on this principle. The law states that if A=B, then any property of A is also a property of B (Guttenplan, 431). The first argument for dualism which I will discuss is the doubt argument, which compares the difference between an idea of one's own existence and an idea of one's body's existence. The argument can be put forward as thus:
Because of the nature of my being, my existence cannot be doubted.
Because of the nature of my body, its existence can be doubted.
Therefore, my mind which is the thinking thing that I am is not identical with my body. (Kim, 36)
So in other words, whilst I can be convinced that I exist, it is not possible for me to know that my body exists with the exact same certainty. However, a response to this could be a comparison with another argument of similar structure but with a false conclusion, for example; Mary-Jane believes that Spiderman is a hero but Mary-Jane does not believe that Peter Parker is a hero. Therefore, Spiderman and Peter Parker must be fundamentally distinct. From this argument, we can see that the doubt argument is invalid.
A second argument for dualism is the divisibility argument which may be reconstructed as follows:
The self or soul lacks any parts into which it is divisible.
The body, being spatially extended, is divisible and so composed of parts.
Hence, the self and the body are distinct substances and the self is, unlike the body unextended. (Lowe, 8)
The basic idea behind this argument is that the body is divisible because it is extended and thus can be separated into any number of parts. But Descartes argues that the mind is not divisible because each part of the mind, despite having different processes, has the same force behind it. Therefore, the mind cannot be seen as an extended entity because unlike extended entities, it cannot be divided into parts. So the same conclusion is reached; mind and body are ultimately distinct. However, the divisibility argument, despite being simple, has the same problem as the argument from doubt. We can't be totally sure that both premises are true. But Descartes was sure you couldn't divide the mind, especially someone's thoughts and beliefs. However, it possible to argue that the mind can in fact be divided, if we consider the mind equal to the brain. Descartes may be right in stating that thoughts, beliefs, memories etc. cannot be divided but the substance that they are a state of, the physical brain, can be separated such as in the case of brain surgery. People with personality disorders or split brains may have a "divided mind". The first premise in this argument can only be true if we see the mind as a substance distinct from the brain. Thus, the divisibility argument is ultimately a weak argument in support of dualism.
The final argument I will discuss is the argument from disembodied existence. Following the previous arguments, Descartes goes even further yet, stating that the mind is not only separate from the body, but that it can exist without it. The argument can be put as follows:
If two things can exist apart from one another i.e. mind and body, they must be distinct.
If I can imagine these things existing separately, God must be able to bring it about.
If God can bring it about that these things exist separately, they must be distinct.
Therefore, it is possible for the mind to exist without the body.
In Meditation VI, Descartes expresses that he knows that all the things that he conceives clearly and distinctly can be produced by God precisely as he conceives them (Descartes, 28). Basically, the point that is being made is that if two things can exist separately, then they may be considered distinct. Descartes appeals to God to strengthen his argument, stating that if God can allow two things to exist separately, they must be distinct. But the problem lies in the fact that just because it is possible to perceive the mind and body as distinct, are they really distinct? Kim uses the example of the bronze bust of Beethoven. The bust could exist without being the bust of Beethoven, for example it could easily be the bust of say Brahms. However, if the bust is melted down, could it exist without being a material thing? The answer is no, as being material is a part of its essential nature and it cannot exist without being considered a material thing (Kim, 40). Thus, whilst it's conceivable that I exist without a body, is it really possible? That is the problematic question that ultimately weakens Descartes' argument.
As I have shown Descartes' argument for dualism to be weak, I will now highlight the ways in which materialism and in particular, functionalism refutes the claim that mind and matter are distinct substances, and fundamentally proves to be the stronger argument. One of the main questions that come from dualism is how the causal interaction of two distinct substances is possible. Materialism states that the universe contains only physical matter rather than distinctions, as in Descartes' case. Whilst there are many strands of the materialist theory, functionalism appears to be the strongest. Functionalism is a theory which concerns itself with the idea that mental states are comprised exclusively by their functional roles. It explains how having a non-human brain can still result in mental states and also manages to explain how mental states can come from matter in the first place, without being completely perplexing. One of the strongest arguments in favour of functionalism is the argument involving the idea that mental states (such as pain) can be multiply realised because they involve functions. Fodor and Putnam argued that the importance of the state of pain does not lie on the c-fibres firing but what they are doing and what their contribution is to the operation. The point is that the role of the c-fibres could have been performed by anything suitable, as long as it was indeed performed (Lycan, 52). Clark puts the functionalist claim in an interesting way: "the mind is to the body/brain as the program is to the physical machine." (Clark, 169) This idea can be seen as a direct response to the dualist view that mind and matter are distinct as the software is the product of material processes rather than being material in itself and any change in the software will cause changes in the computer's physical components. Furthermore, it is impossible for the software to function without the hardware and vice versa, indicating that there is no real distinction between the mental and physical.
Ultimately, as I have argued in this essay, I believe Descartes' dualist theory to be wholly unconvincing. This is primarily due to the weakness of the three arguments highlighted but also, the lack of strengths that appear in the theory. Descartes is convinced that mind and body are distinct but substance dualism doesn't seem to give an explanation as to why exactly mind and body are distinct and what the purpose of this distinction in. On the contrary, functionalism, a strand of materialism is a far more convincing theory in the discussion of mind and matter. By stating that there is no distinction between the two and that in fact, a mental state is concerned more with its function and its role in the wider system, an analogy can be made between the mind and a computer programme. This analogy is possible to conceive and essentially makes sense. So overall, substance dualism proves to be a far weaker argument in comparison to functionalism.