While it is strongly argued, Descartes’ assertion of the distinction between mind and body fails to convince many of his critics. He has particular problems when it comes to the conception of a mind without extension and with proving that it is logically impossible for the mind to have extension. Even if he overcomes these hurdles, he is struck by the infinitely more complex riddle of how these “distinct substances” interact.
In this essay I shall outline Descartes’ arguments for the distinction between body and mind, and then discuss the merits and demerits of Cartesian Dualism. In the process of this I shall come to a conclusion as to whether the obstacles to Dualism are insurmountable, or whether they can be overcome. Building on the assertion of the cogito, Descartes attempts to discover the nature of this “I” that he now knows exists. His meditations lead him down the path of what has now become known as Cartesian Dualism – the assertion of the distinctness of mind and body.
Descartes states that he has a clear and distinct perception of his mind as a purely thinking substance; one of which the essence is thought and thought alone. Critically, he states that he can conceive of the mind as existing without the support of any other substance, specifically without the body. Next, he turns to the examination of the body, which he conceives of as pure extension, having no capacity for thought whatsoever. Thus, he says, mind and body have completely separate and opposite essences, and are distinct.
Descartes goes on to provide more detail about how we know of the existence of external objects, and how the mind and body interact. He first distinguishes between imagination and understanding, saying that imagination involves a mental picture of the object concerned, whereas understanding is merely concerned with grasping the essence of the substance. I can understand a 1000-sided object, but cannot imagine one precisely. According to Descartes, the essence of our mind is in understanding, and it could exist without imagination.
However, imagination is the faculty by which our mind conceives of external objects, in conjunction with the senses. Thus, imagination is part of the interaction between body and mind. The senses are the other faculty that links mind and body, and also provide Descartes with part of his reasoning for the existence of external objects. The senses are the means by which things that happen to our body are transmitted by nerves to the brain, which transfers information about pain, hunger, etc. to the mind.
As we are in control of our minds, but sensory experiences are involuntary, Descartes reasons that they must be caused by something outside of ourselves. As God is not a deceiver and would not randomly implant sensations that were illusory in us, they must come from external objects. God also guarantees that the majority of the time, so long as we investigate as fully as possible, sensory perceptions are to be trusted. We can summarise Descartes’ arguments as being that, “I can doubt that I have a body.
I cannot doubt that I exist, or that I am a thinking thing. Therefore, I who am doubting am not a body. ” It is from this that Descartes draws the conclusion that the mind and body are distinct. This argument, however, is based on entirely false logic. But if we refer to Anauld’s objection by way of a parallel argument, it is possible to prove Descartes’ argument as hollow. It is quite possible to doubt that a right-angled triangle has Pythagorean properties (that the length of the hypotenuse equals the sum of the other two sides).
But just because I doubt that a triangle holds these properties, it does not mean that the triangle actually lacks them. On the contrary, geometers can prove that, regardless of my doubts, Pythagorean properties are, in fact, part of the essence of a right-angled triangle, and thus it is not possible to have a right-angled triangle without these properties. Thus, by parity of reasoning, it seems perfectly possible that despite my imagining myself without a body, my body is, in fact, an essential part of me.
Thus, although Descartes repeatedly states that mind and body are distinct substances, he does not give much justification or proof as to why it is logically impossible that they be joined. An objection raised by Gassendi was that although we clearly and distinctly perceive that the essence of the mind is thought, there is nothing in that perception that prevents the mind having extension. Descartes’ reply was an affirmation of his conception of substances. According to him, a substance is something complete in itself, not lacking in anything.
If the mind can be conceived as a thinking substance, then it is complete as a thinking substance: an indivisible unit. Though there may be a union of body and mind, this can be split into the two sections, but the mind cannot then be divided further. This reply raises several objections. The first is that if the body is a complete substance, how is it that it could be divided further into various body parts, organs and so on? Descartes might answer that a body without any part would not be complete; to which the response would be that it would still be a complete liver or eye.
Nevertheless, it must be conceded that no body part could exist on its own (although the body is perfectly capable of surviving without a limb, a lung or a kidney for instance). This brings us to the next objection, that we cannot conceive of a mind solely as a thinking thing, existing without any form of extension. The mind itself rebels at the idea – a substance without extension, without any occupation of space, is not something we can conceive of as a substance, but more as a property or faculty.
We can conceive of thought itself as without extension, merely something that happens, some process of the brain. Probably the most useful interpretation of mind from the point of view of defending Descartes is simply to see it as synonymous with thought. The mind is simply the faculty of the process of thought, and imagination is a specialised (though non-essential) form of thought relying on sensory information for its construction. Nevertheless, Descartes still has to show that it is logically possible for the mind to exist on its own, without being a part of an extended body.
Though we are able to conceive of thought as a faculty that is not extended, we cannot conceive this faculty existing on its own; it is always seen as the faculty of a body to think. Thought itself may not be extended, but it is incomplete as it stands along – it must always be a process happening within a body, and is thus not a distinct, complete substance as Descartes seems to think. So when Descartes argues that, “the soul by which I am what I am… is entirely distinct from the body… and would not fail to be whatever it is even if the body did not exist” he is rather mistaken.
We may concede that the body is distinct from the mind (though the degree of separation between the physical organ of the brain and its cognitive process may be debatable), but this does not mean that the body is separate from the mind, nor that the mind can exist without the body. Certainly the brain cannot exist without the body, and if we take modern empirical scientific evidence, then the process of thought, or whatever other thinking capacity Descartes cares to conceive of cannot take place without the brain, and thus cannot take place without the body.
Thus, mind and body may be distinct, but they cannot exist without one another, and are not therefore separate. Descartes’ statement that “it is certain that I am really distinct from my body and can exist without it”, seems, certainly to modern ears, a counter-intuitive notion. How exactly does Descartes know that he could exist without a body? Presumably he believes that without a body he would still be able to think, and as long as the cogito can be asserted, regardless of the existence of a body, he exists. But how does he know that he could continue to think without a body?
It seems, as Cottingham notes, that Descartes views thinking as an entirely transparent process, whereas we, with the benefit of advanced medical knowledge, understand it to be a physical process. We must recognise that Descartes is not referring to the soul as distinct from the body; that is an entirely different, though initially more acceptable, argument. But as we understand thinking to be a physical process, we are forced to conclude that it requires the body, and one cannot think, nor exist without a body. In short, one’s body is a central part of one’s essence.
Perhaps more so, even, than thinking is. (Consider a mentally-handicapped person, incapable of independent thought, who clearly has a body. It would be difficult to assert that they do not exist). So although we may concede that usually one can clearly and distinctly perceive that one is a thinking thing, whereas to clearly and distinctly perceive one’s body may be harder, this does not entail the two being separate entities. Hobbes’ argument concurs with modern science when he asserts that “that which does the thinking may well be something corporeal”, indeed Descartes has not proved otherwise.
In any case, if we accept Descartes’ distinction between mind and body, this leaves him with the not insignificant problem of explaining their interaction. His initial attempt is somewhat vague, specifying a point in the brain to which all of the body’s nervous signals are directed, and which somehow transmits information to the mind. Yet it seems impossible that there could be some interaction between a point in the brain and something completely non-extended, consisting only in thought.
The body’s information will be transmitted in terms of extended things, as this is its essence, whereas the mind will only be able to communicate via thought, as it is complete as a thinking thing with no other capacity. One would have thought that for an interaction to take place there would need to be some form of contact, something in common: the information would have to be transferable. As it is, neither can receive the information from the other, as it is in a form that is contrary to its essence – the mind cannot receive experiences presented as extended things, nor can the body comprehend thoughts.
But to come to some sort of conclusion, and to summarise the objections to Cartesian Dualism, we are forced to find that the objections certainly do emerge as insurmountable obstacles. The most contraversial, and problematic, element of Descartes’ argument is his insistence on the non-corporeality of the mind, which I have proved to be totally counter-intuitive and totally contrary to any understanding of modern physiology and neurophysiology.
As Kenny argues, “Descartes’ claim that an act of thinking or doubting needs no place and depends on no material thing… is simply preposterous”. And the second major objection regards the interaction between body and mind. Descartes even admits that we are aware from experience that the mind acts on the body and vice versa. But since he defines mind and body as not merely distinct entities, but as mutually incompatible entitites, it is difficult to find how a causal flow between mind and body is possible.
This is especially difficult as Descartes also argues that “causal transactions require some relationship of similarity between effect and cause” but, following Descartes’ argument this should be simply impossible “given the logical gulf between them”. Thus, we may conclude that Cartesian Dualism does indeed face ‘insurmountable obstacles to it’ and thus Descartes’ account must be rendered a failure, in part due to his lack of medical understanding (as we understand the mind and body) but also due to his incompatible arguments.