Topic 3 - "Sum res cogitans."

"Sum Res Cogitans" or "I am a thing that thinks" is the conclusion Descartes reaches in Part Four of the "Discourse on the Method" using a similar line of reasoning to that adopted in the Meditations, namely by way of a process of doubt. He also examines the theme once he has proved his existence in the Second Meditation; what, he asks, is the nature of that which he has deduced to exist from the Cogito argument? As he is still without evidence for the existence of his body, he must restrict himself to the functions of the mind. To this end, he says "What am I? A thing that thinks. What is that? A thing that doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and has sensory perceptions."1
Furthermore, in the Discourse, Descartes also concludes that this soul2 that he consists of is entirely separate from the body, and is perfectly capable of existing without a body. His argument is summarised by one of his objectors, Arnauld, in the Fourth Set of Objections as follows: I can doubt whether I have a body, but I cannot doubt that I exist. Therefore, I who am doubting and thinking am not a body. If I were to have a body and have doubts about it, I would be doubting myself.
Arnauld then goes on to discredit this argument completely. He cites the example of a right-angled triangle; I may doubt that the triangle has the square on its hypotenuse equal to the sum of the squares on the other two sides (Pythagoras' Theorem), but my doubting that the triangle has this property does not prove that it doesn't actually have it. In fact, I would be wrong to say this, as geometers can prove that this property does exist for right-angled triangles. By abstraction, to say that I can imagine myself as without having a body does not preclude the possibility of my having a body; indeed, as with the above example, the possession of a body may be entirely necessary to my existence, just as the right-angled triangle must be susceptible to Pythagoras' Theorem.
However, just as when Descartes was introducing the concept of doubting all data he received from the senses did not hold that this meant that the senses deceived him all the time, so in proposing that his essential nature is that of a thinking thing does not automatically exclude the possibility of the existence of a body. In the synopsis to the Meditations, Descartes made clear that his intention was not to suggest how things might actually be, but to examine how it seemed to his intellect alone, given the premise that he could not trust his senses; once this premise was modified or dispensed with, it would be perfectly plausible to say that a body was a part of his nature. His conception that he does not have a body must be tested to see whether this corresponds with how things really are. Unfortunately for Descartes, his use of the phrase "I am, then, in the strict sense only a thing that thinks;" in the Second Meditation seems to unduly exclude the existence of a body. Indeed Gassendi, author of the Fifth Set of Objections made much of this, and Descartes is not entirely convincing in his attempts to avoid committing himself to this implication.
This, then is the "Argument from Doubt" that attempts to prove the non-materiality of the soul; Descartes returns to this area in the Sixth Meditation with what has become known as the "Argument from Clear and Distinct Perception." This runs that, as I am aware of my nature as a thinking thing as being non-extended, and I also have a concept of a body as being a non-thinking, extended substance, then the two are different; the mind is distinct from the body, and can exist without it. The two are distinct, as they are capable of being separated by God, if not by man. The same would apply to any two substances that can be perceived distinctly. Is it correct to say that just because I perceive two substances separately, then they really are distinct? This proof appears to be as susceptible as the former argument; indeed, Arnauld uses the very same example as a case against it. I could perceive a right-angled triangle as being right-angled, but without recognising that Pythagoras' theorem must be true of it. On Descartes' reasoning, I would be justified in saying that the two properties - that of being right-angled and that of having the square on the hypotenuse equal to the sum of the squares on the other two sides - are separate because I perceive them distinctly. However, this is clearly not the case; any right-angled triangle must also have the property as discovered by Pythagoras. Not even God can create a right-angled triangle that does not have this property.
Descartes replied by saying that the parallel was an unfair one; neither the triangle nor the property, he said, could be understood as a "complete thing" in the way in which body and mind could be. By this he means a substance; something that can exist on its own. His concept of his mind is complete in that his awareness of his own thought is a sufficient attribute for him to exist without any other attribute. This awareness is the only attribute necessary for his mind to be a complete substance. He may have other attributes of which he is not aware, but as they are not necessary for completeness, they can be said not to be a part of the essence of the mind. Thus the Pythagorean property of a right-angled triangle is a part of its essence; the triangle is not complete without having that property. As Arnauld himself had noted, the two could not exist apart. So this seems a valid reply to the objection raised.
This does not, however, explain how the mind could exist independently of the body, or at least some part of it such as the brain. Although twentieth-century medical and scientific knowledge appears to offer us an advantage over Descartes in these areas, such suggestions that thought might be a physical process were put forward by some of Descartes' critics; Gassendi said that it was not possible for a mental operation to take place outside or independently of the brain, and Hobbes believed that thought was indivisible from the matter that was doing the thinking. So it seems that Descartes is on shaky ground here. Furthermore, if thought is independent of physical condition, why should people suffering from coma appear to have impediments to the operation of their mental processes. The fact that their body is damaged should not, according to Descartes impinge on their thought processes. Yet the evidence appears to point to the contrary, that extreme physical ailment damages the thought processes as well; this would suggest that a functioning physical body was needed to enable thought and other mental processes. In short, Descartes has not shown that that which does the thinking is not corporeal.
Descartes' third argument reinforcing his belief that he is separate from his body and could exist without it is the "Divisibility Argument." Concerning his ability to distinguish between mind and body, he believes his body to be extended, i.e. something that is capable of being divided, whereas he cannot conceive of his mind being divisible in this way. To illustrate this point, he offers the example of having one's foot or arm cut off, and not losing any mental faculties. This does appear highly doubtful; although it may be true for a limb, it is almost certainly false were one to apply the argument to a part of the brain. Damage to the brain as the result of a stroke certainly diminishes mental ability, Descartes allows that there are some mental processes such as imagination and sensory perception that do indeed rely on the brain. On the other hand, he insists that were the body to be destroyed completely, the mind would not be harmed; what he refers to as "pure thought," such as an abstract perception of the intellect, can occur totally independently of the brain and body.
Despite the fact that medical evidence in cases of dementia, coma, and amnesia would seem to suggest that this survival of the mind beyond bodily death is highly improbable, Descartes believes his position to be impervious from assaults of this nature because it has already been established that the soul is quite distinct from the body. He also claims that the mind continues to think even when we are asleep, during early childhood, or even before birth when in the womb. This follows as a result of existence; as long as something exists, that which constitutes its nature must also continue to exist. Thus, as long as my mind exists, it must continually think.
As for the non-divisibility of mind, Descartes does seem to have a point. We cannot, he says, conceive of half a mind, but we can conceive of half a body. This seems sensible enough. He runs into difficulty in trying to counter the conviction that was around even in the 17th century that the mind is capable of being divided into several faculties, such as will, sensation, understanding, etc. Descartes maintains that it is one and the same mind that wills and understands, and as such, all of these actions of consciousness are referred to as the same "I." Nevertheless, this raises problems when talking about "being in two minds" over something, which one part of us tells to do (e.g. finish an essay), and another that says to do the opposite (leave it until later, to use polite terms). Although language undoubtedly leads us to believe in one centre of consciousness, these and similar examples would suggest that the mind is not as indivisible as Decartes might claim. Ultimately, even if consciousness is indivisible, there remains the possibility that it requires a physical structure (i.e. the brain and central nervous system) to function, and it is certain that these physical structures are divisible.
From examination of these arguments, it is clear that the Cartesian argument fails to convince that the mind and body are separate and different substances. Even if one were to subscribe to this reasoning, there are further problems concerning the interaction of the two. There are a myriad of examples where mental sensations produce physical responses and vice-versa; the defining of body and mind in mutually exclusive terms begs the question against Descartes of how the two are to interact together. When Burman asked Descartes about this, the only response Descartes was able to supply was that this was a difficult issue, but our experience was sufficient that it could not be argued against, which seems a complete non-answer. Add to this the difficulty of where this interaction is supposed to take place. Despite coming up with the pineal gland in the centre of the brain as a location, given that this is the only place where data from the different senses could converge, this still does not solve the problem of how the incorporeal soul can act on the corporeal body, so as to produce movements in this gland that cause a bodily reaction to stimulus.
In conclusion, Descartes has failed to argue definitively that the body and soul are distinct substances in the way he perceived them. Although he is correct in saying that our essential nature is that of a thinking thing, to say that this can exist independently of matter seems highly far-fetched.
Notes:
1) Second Meditation (CSM II 19)
2) Descartes used the word "soul" synonymously with the word "mind;" there was no implicit spiritual meaning in the term.