�The body is a great
reason, a plurality with one sense, a war and a peace, a herd and a shepherd.
An instrumnet of your body is also your little reason, my brother, which you
call �spirit� �� � Nietzsche, �On the Despisers of the body�
Descartes uses three main arguments to establish his conviction that the body and the mind can be distinguished, and are in fact distinct. He quickly defines himself indubitably and essentially as a mind, a �thinking thing�, i.e. a substance whose essence is thought. In contrast to body, minds have no extension � they take up no space, and are indivisible. It is not until the very end of the Mediatations that he re-establishes the existence of an external world, much as it first seems to us, including a body in which we operate in the corporeal world.
Importantly, he states early on that he can conceive existing without his body, yet could not conceive of his existence without his mind. In fact, this distinction between the two, known as the Argument from Doubt, leads on to the Cogito. But its purpose is to establish immediately the idea of himself as primarily and essentially a res cogitans, and to set the scene for the two later and more cogent demonstrations of the distinction. In fact, as Arnauld shows with his example of the properties of a right-angled triangle, it seems perfectly possible that, despite Descartes� ability to imagine himself without a body, the body is still an essential part of him.
This can be attacked from various angles. Obviously, it is subject to the proofs which have come before it, and Descartes� explanation of God�s lack of deception reconciled with our proneness to error. It also rests on Descartes� restriction of his essence to being a �thinking thing�.
When Descartes is pressed by a similar version of Arnauld�s attack on the argument from doubt, he introduces vaguely the notion of the mind being a �complete thing�, because it is a substance which can exist on its own, i.e. thought is sufficient, and the mind requires no other attributes. Not only would he be aware of other such attributes, claims Descartes, but more importantly, since these other attributes are not essential to the substance�s independence of existence, they cannot be a part of its essence (tautologically).
As shown below, this non-corporeal purity cannot be maintained in the face of subjective phenomena which have a physical explanation. The critical objection is simply that Descartes cannot be sure that he could continue to think and assert the Cogito without his body, because he might need certain of its corporeal attributes in order to think. As Hobbes put it, �It may be that the thing that thinks ist he subject to which mind, reason or intellect belong, and this subject may be something corporeal�.
Descartes defines the properties of mind and body in mutually exclusive terms, on the basis of extensibility and divisibility. In order to draw this contrast, he has to of course first assume divisibility of matter, or body. Matter itself is divisible in most senses of the word (at least down to the atomic or quark level, where it appears to become quantised into building blocks), and our bodies can be similarly cut up into tiny pieces. But on the other hand, they are still clearly delineated by a membrane or barrier (usually skin), and so in another sense are a single unit, and we can usually say what is or is not a part of our bodies. However, we will grant him that compared to mind which seems to occupy no place or area in physical space, matter is extensible and divisible.
Unfortunately, his certainty that mind is indivisible, since we cannot conceive of �half a mind� or that it has parts, seems an especially strained conclusion to the modern reader. Though a crucial notion, it proves one of the most problematic when trying to incorporate new ideas into Descartes� system. The idea of discrete mind has been inexorably replaced by a complex modular one, and he even goes some way towards it by considering that dreams could be somehow internally-generated, or at least not reliant or resulting from the external world. The indivisibility of mind is linked to the notion of �perfect transparency� necessary for the Cogito. And after all, even if Descartes� consciousness is unitary (as our language prompts us to believe, with its easy-access pronoun, �I�), there is nothing to say that the substance of which it is made is unitary too.
Having considered the arguments Descartes uses to establish dualism, it remains to see whether such a distinction can make sense.
There are cynics who see the Meditations in the light of the intentions outlined in the Letter to the Sorbonne. There are even those who point to what happened to Galileo when his discoveries created difficulties for the Church to resolve, and claim that Descartes chose the easy life by ensuring that his treatise fitted largely with religious doctrine. But assuming, as seems very likely, that Descartes really held his religious beliefs, one wonders whether a religious motivation underlies Descartes� entire enterprise and dictates its course. Of course, if his arguments are solid, then his motivations would be almost irrelevant.
But despite the superficial appeal of dualism, Descartes� formulation of it is so strained in some areas that the reader might be forgiven for wondering. Leaving God aside, the equivalence of soul and mind is the obvious first step to proving the immortality of the soul. To do this, he has to assign our essence as being �thought�, couched in such terms as to include the functions of the traditional soul. He also has to downplay the value and bond to our bodies in order to leave free the possibility of the soul�s existence continuing after the trivial �change in shape and configuration� that is death; Plato�s strained metaphors and arguments are testament to the difficulty of directly proving that we have an immortal soul. This absoluteness leads him to further untenable conclusions, such as that the soul is continually thinking, assumedly even during breaks in wakefulness (but during unconsciousness too?). In conclusion, though Descartes would find some aspects of his dualistic distinction easier to explain, it couldn't be claimed that it is solely Descartes� religious agenda which undermines his dualism.
Perhaps the single largest problem for Descartes� dualism lies in the sharpness of the divide between mind and body. He leaves almost no room for the interaction between the two that takes place, for instance when events in the corporeal world cause the subjective sensation in my mind of pain. On the other hand, later writings which talk of scarcely-understood mechanical or �gravitational� forces acting on a mind located in the pineal gland hardly simplify the issue of how our will acts back on the body in the form of motor control. Descartes admitted his bafflement regarding this insoluble �ghost in the machine� in his conversation with Burman. Indeed, the psycho-physical even clouds the purity of his definition of �thinking�, when it becomes apparent that �imagination� and �having sense perceptions� involve the body by Descartes� own admission.
Descartes� ends up implying almost trialism, with his list of �primitive� categories having to include a �union� of body and mind to accommodate the �sensations and passions� � this is what he admits in a letter to Elizabeth in 1643. Such a trialism would be necessary to distinguish between animals and inanimate objects, although Descartes carefully avoids that this third category is distinct in ontological, as opposed to epistemological terms. Perhaps it would be easier and make as much sense to say that it is these subjective phenomena are primary, with thought being abstracted from them and matter being acted upon as a result of them.
Strawson sees the fundamental difficulty of the Cartesian standpoint as being one of identity: how �I� can be sure what �I� am and where the �I� stops. He claims that it is only by seeing the mind as being a feature of body, just as a surface needs a table to be a surface of, or (to use one of Descartes analogies) a mountain and a valley are inseparable. Strawson attacks the intelligibility of the idea of mind without body by attacking the idea of a conscious Self being able to identify itself as a unique and enduring entity. He uses Margaret Wilson�s query of how such a consciousness would be able to differentiate itself from any one of a plethora of consciousnesses, all simultaneously thinking the same thought. He also uses Kant�s attack on Locke�s theory of the Self�s assurance of unity through time because of memory: though we are conscious of ourselves as having a �stream� continuously flowing uni-directionally through time, why might we not be a succession of evolving, static mental states? Strawson�s anti-Cartesian stance says that we can only regard ourselves as a �person� when we have a body to give us identity as an individual, with applicable criteria for establishing and delineating our presence.
Yet I cannot see how the body is any less subject to both arguments � why might not a body be inhabited by many identical consciousnesses all dictating the same actions simultaneously, unaware of their cohabitance? Descartes doesn't address the problem of multiple consciousnesses, although if they are indistinguishable and never deviate, they are all �I�. And as for the body�s continued existence through time, Descartes did consider this, taking recourse in God to preserve us through continual re-creation. For those who find this unsatisfying, television is the most powerful example of how easily we can be fooled by the illusion of continuity when faced with a rapid succession of discrete instants, depriving us of confidence about our body�s continued existence in time. So it seems that Strawson is providing no greater assurance of personal identity by describing ourselves as body-minds than a dualist Cartesian can.
Moreover, Strawson ignores the issue that Hume raises, of whether we can meaningfully talk of a central �Self�, as Locke and Descartes assume. Russell notes that a parallel between Berkeley�s removal of substance from physics with this repudiation of substance in philosophy of mind. When Hume tries to centre on �myself�, he always stumbles on some particular perception or other, never managing to catch the myself at any time without a perception, and never being able to observe anything but the perception. The echoes of this argument are still audible in the contrasting substrate and bundle models with which Desscartes� views on how properties adhere to objects can be understood.
The �powerful illusion� (as Kant termed it) of dualism is that, even in the context of modern neuroscience and strong philosophical arguments against it, it feels intuitively valid somehow. In short, my mind �feels� different from my body.
The fact that Descartes� most infamous declarations figure prominently in every modern physiology textbook is a testament to the importance of the issues he addresses. However, the same textbooks unanimously declare his dualistic explanations to be outdated, in line with the prevailing view that the complexity of the nervous system (and possibly the rest of the body) provides sufficient explanation in physiological terms to account for the mystery of consciousness, which is the direction in which the debate has shifted. It seems appropriate to spend a little time reviewing whether current thought on the subject can be reconciled with Cartesian notions.
In partial defence of a dualistic metaphysics, Nagel�s quest for objectivity parallels the method of doubt. When discussing mind�s relation to body, Nagel feels able to dismiss what he terms a solely �physical conception of objectivity� in a few short pages. He describes three phenomena irreducible in monistic, purely physical terms: the qualitative jump to subjective phenomena and features of conscious mental processes; the fact that even though we can �climb outside of our own minds� to a centreless, featureless �bleached-out� conception of the physical world, this does not explain where these perspectives and specific viewpoints �left behind as irrelevant to physics� come from; and the mental activity involved in analytically objectivising our viewpoint in the first place.
Perhaps the most powerful evidence that the mental can somehow be expressed in corporeal terms stems from the field of neuroscience. This evidence has an empirical basis, which of course strictly depends on the rationalist constructions of the first five Meditations for its validity. That aside, there can be little doubt that our minds are influenced by the physiology of our bodies in a far more direct way than Descartes could have envisioned. With minimal hyperbole, science can claim to have given crude sight to the blind by producing coded neural impulses in the visual system of the brain, which equate to subjective phenomena like edges and colours.
Body�s erosion over mind is complete for most theorists. However, misconceptions and considerable debate remain over just how the brain�s structure could produce consciousness. To illustrate, I will outline two models.
The Higher-order theory (hot) focuses on the ability to have thoughts about thoughts (or doubts about doubts), i.e. mental events which don't take direct perceptions as their object, but each other. It is difficult to conceive how the state of an array of neuronal activity can take its own state as the internal representation being formed, unless we take the obvious step of compartmentalising the various functions of the brain, e.g. perception, working memory, language etc. However, this shatters yet another Cartesian premise, the indivisibility of mind. Damasio�s comprehensive attempt at an explanation of �emotion, reason and the human brain� further reduces the credibility of an indivisible mind, with its explanation of the seeming unity of our awareness in terms of the synchronicity of mental activity in separate areas of the brain.
Dennett�s �multiple drafts theory� posits a complex machinery of independent and limited �agents� in the mind; the mental pandemonium that results from their interaction is enough to generate goal-directed behaviour and conscious cognition. This illustrates Dennett�s keenness to avoid the misconceived scenario of a homunculus inside a �Cartesian theatre� which arises when we think about a �Self� at the highest-order controls of our thoughts.
It remains to say that Descartes� arguments for mind/body distinction are amongst the most contested in the Meditations. Moreover, his own writing betrays the incompatibility inherent in dualism, and the difficulty of incorporating the subjective phenomena which take both mind and body as their domain. Now, with fairly plausible explanations of a materialist basis for mind, the alternatives to dualism appear even more compelling, despite its intuitive attraction.