Descartes� noble, if immodest, quest is founded upon his �method of doubt�. By first ridding at least the meditative portion of his mind from all uncertain pre-conceived notions and beliefs, he hoped to build an epistemological system upon self-evidenced,� unassailably certain truths.
The development of this project of doubting through suspense of judgement is traceable to earlier works like the Regulae and Discourse on Method, where he formulates rule-based, prescriptive sets of steps. His method is intended to be useable by anyone of reasonable intellect, and to ensure absolute certainty in its conclusions, if absolute certainty is attainable. Just as the modern scientific method provides empirical verifiability, Descartes relies on the �natural light� as his criterion of truth. With this as a standard, it should naturally follow that any adherent to the method of doubt should draw the same conclusions. This could perhaps act as a means of judging the success of the method of doubt.
There are perhaps three main ways in which attacks can be levelled at the method of doubt in the Meditations: on the concept of a �method of doubt� as being unoriginal and superfluous; on Descartes� failure to implement it according to his own rules, whether through possibly subconscious self-delusion or human error; and on flaws in the metaphysical underpinnings of the method of doubt.
Hobbes dismisses Descartes� discussion of the dubitability of sense-perception and wakefulness as �ancient material�, and questions whether Descartes� attempt is something original worthy of fanfare. Surely, every system-builder must first establish the fundamental premises which underpin their conclusions, even if they lack Descartes� explicit� guidelines.
What exactly Descartes means by �doubt� is obviously an important question. The �practical� everyday doubt to which we are accustomed usually refers to our denial of a belief (�I doubt that�), or reservation of judgement between two conflicting propositions, often resolvable by an empirical or other accepted criterion. Moroever, closure is �contingent on the current state of knoweldge�.
On the other hand, Descartes� metaphysical doubt is a deliberate with-holding of assent, by power of the will for as long as the intellect apprehends it without complete clarity and distinctness. After all, to positively deny an uncertain proposition would be as risky as to affirm it. As Michael Williams perceives in a contrast with classical Greek scepticism, Cartesian doubt is stratified, i.e. built up in deepening layers, such as the three arguments in the First Meditation to doubt the senses (because they sometimes lead us to erroneous conclusions, the argument from dreaming and the idea of the malicious demon). Since the available knowledge is not perceived to change, only to grow layer by layer, doubts replaced by beliefs are not ephemeral, but final. Having said this, there is a curiously time-indexed way in which beliefs are held, doubted and then re-affirmed once more.
Thus, Cartesian �metaphysical� doubt could be said to be rather different to �practical doubt�, besides the degree of caution and the nature of the propositions being doubted.
Many Descartes readers are disappointed when the high ideals espoused in the First Meditation seem compromised in later, key sections, notably the proofs of God. It seems suspect that Descartes� explicit aims were to prove that the framework erected by science is on solid ground, as well as justifying often-voiced religious beliefs in God and the immortality of the soul. However, just because these pre-conceptions coincide with his conclusions does not detract from the value of his work, as long as Descartes� arguments stand independent of Descartes the man.
Descartes employs more implicit metaphysical �truths� than he recognises, besides baldly stating various scholastic maxims integral to the coherence of his proofs. It is difficult to know whether he is aware of how often he takes for granted doctrines untested by the method of doubt, such as the �perfect transparency of mind�, by which he assumes that he is necessarily aware of his thoughts, and that they are somehow free from the impossibly subtle tendrils of the malicious demon.
However, especially in his specious proofs of God, he makes liberal use of statements such as, �what is done cannot be undone�, �it is manifest by the natural light that there must be at least as much reality in the efficient and total cause as in the effect of that cause� and describing preservation as equivalent to a continual process of re-creation, both of which arguably lack sufficient clarity and distinctness to hold up in proofs of God. In fact, entire swathes of the Third Meditation hinge on suspect definitions such as �objective� as opposed to �formal� reality, besides the shakiest premise of all, that of a supreme, perfect (in a very anthropomorphised, Christian way quite different to the amoral connotations of �infinite�) God who numbers unity amongst his properties, and so also must exist. Despite having piously described and ascribed so much to God, Descartes shiftily hides behind the defence that his nature is ultimately inexplicable to us, whenever faced with questions such as �Why would God create us?� and �Would he definitely admit himself to be discoverable?� Moreover, his own religiosity is evident in his failure to question gaps between the simple ideal world constructed eventually and our real world � for instance, if our free will has been given us complete by God, why are we deprived of the will to suicide? After all, why is dying a bad thing, given how divorced from the body Descartes describes the mind as being?
There are other fundamental concepts which need to be taken on board before the Cogito can be applied, such as what an object is, �truth� and �certainty�. These are concepts embedded within the method of doubt, and so not evidently subject to its scrutiny. Descartes himself seems unaware of them until writing later in the Principles, where he is forced to admit their pre-supposition.
Descartes regards dreams initially as an insoluble source of confusion to us regarding the external world. Five Meditations later, he highlights memory and continuity, quite independently of any extra premises or the existence of God, as being our safeguard against mistaken wakefulness. There is no explanation why the method of doubt failed to supply this same answer through the natural light when the question first arose; instead, dreams are used to lend plausibility and weight to the argument that we cannot trust our sense perceptions.
Any argument from dreaming will be difficult to settle confidently because dreams assault the usually sure sanctitude of our mental life, and only imperfectly admit the scrutiny of our consciousness. Given that all modes of thought can perhaps be experienced within dreams, including obviously sense perception and even rational thought (monitored in sleep laboratories during what are known as �lucid dreams�), there seems to be no dream test which could conceivably discern our dream state while dreaming - or awake for that matter.
Therefore, the only recourse seems to be the familiar one, i.e. that God would not let us be deceived by dreams our entire lives (even though he does it a little bit occasionally). This is even more unsatisfying than the parallel authentification of our senses he adduces, especially as it leaves unanswered why dreams should be considered less �real�, in any sense of the word, than being awake. In fact, although Descartes is more original than Hobbes gives him credit for by elevating the dream state from a delusion to being an experience of sensory perceptions without physical causes, he still falls short of fairly comparing its �reality� to the wakeful state (which has breaks and differing levels of consciousness and coherence too).
Descartes sets two circularities spinning in opposite direction in his argument: on the one hand, a supreme and perfect, inherently good God acts as guarantor of our knowledge while on the other hand, the supremely powerful and cunning maliciously subversive demon seeks to lead us astray wherever possible. Dismissal of the hypothetical demon through God�s existence rests on a proof of God which could itself be subject to the demon�s influence. Thus we find ourself in as potentially inextricable a position as with the argument of dreaming � there seems to be a starting level of doubt and uncertainty beyone which there is no Archimedean point from which to proceed. In this way, Descartes may have slipped a spanner into the works of his own mechanism by introducing the evil demon, who is not not really that different from the God he goes to such great lengths to prove.
The method of doubt itself has flaws independent of the topic being investigated with it. Hume numbers amongst those who simply believe that Descartes� demands of those (including himself) who wish to employ the method of doubt are impossible. In fact, it is not clear whether our will, which he describes as digital, would be capable of with-holding assent, as opposed to merely opposing or denying.
Although Descartes� methodology is as precise as he could make it with regard to the elimination of uncertainty, he becomes almost platonically mystical in his descriptions (also using the visual metaphor) of how to judge when a proposition is certain and true. The Cogito is described as �self-evident�; indeed, Descartes shied away from attempts to formalise it in a syllogy, stressing the importance of the meditator being able to hold it conceptually in order to be able to use it to affirm his existence. Does this mean that only plainly self-evident truths can be intuited? Some sort of
Despite attempts to make the method of doubt almost mechanical, an ineliminable element of forward-reasoning remains, requiring something personal and inexplicable from the meditator in order to progress. Indeed, the jump from blackness to the Cogito could not have been guided by the natural light (for Descartes did not identify it until afterwards). Further intervention is necessary in judging the level of �clarity and distinctness� sufficient in propositions which are to be held certain.
The notorious circularity in the Meditations is also manifest in the problem of selecting �true� truth criteria. Descartes uses the �clarity and distinction� as shown by the �natural light� as the criteria for judging the certainty/truth of a proposition, but he effectively used those same criteria in choosing them as the criteria. Although he devotes a great deal of space to discussing why we commit intellectual errors sometimes, while simultaneously refusing to accept that God could allow us to be deceived, he fails to aid the reader since his own criteria are neither clear nor distinct themselves.
The fact that Descartes concluded by establishing the truths he held most dear at the beginning of the Meditations could be a result of the fact that that was the direction in which the natural light happened to shine most clearly and distinctly for him; perhaps others, following his procedure assiduously and being guided only by what seemed wholly clear and distinct to them, might conceivably be led in different directions. Indeed, this is what one might expect to happen if there is no absolute universal certainty attainable in this manner. Some might simply find that no natural light clears the maelstrom of metaphysical uncertainty. As is obvious from the lack of universally-accepted progress, this myriad of opinions is in fact what we find in men who attempt the method of doubt.
The idea of absolute (unimprovable level of) truth or certainty should itself be considered uncertain. That there is a sole accessible truth underlies Descartes� entire enterprise. But a problem still remains in the differentiation between certainty and truth. On the one hand, it could be said that if one is certain of something, one is by definition certain that it is true. On the other hand, one can be wholly certain of something which happens to be untrue. These two irreconcilable relations between certainty and truth leave Descartes unwittingly in a quagmire with regard to his immediate aim of being certain of his conclusions, since they may or may not take him any nearer the truth than opinion.
Other technical objections can be raised to the way in which Descartes treats doubt. The way in which he razes to the ground the edifice of his knowledge by doubting a few choice principles evidences his view of knowledge as being built upon foundations. Critics have suggested that it could as well be a web of inter-connected understanding, where the epistemic weights is evenly distributed. Alternatively, doubt might not be culminable, i.e., although no single proposition is indubitable, there is a maximum proportion of our pre-conceptions we can doubt, beyond which the doubt becomes meaningless.
Despite the efforts Descartes makes to detail his procedure for assenting only to that of which one can be absolutely certain, there still remain many areas in which a serious reader would claim he has strayed. By the Sixth Meditation, he has been swept up by his own fervour, to the extent that even basic empirical falsehoods regarding pain and the nervous system are admitted with minimul scrutiny. That there is such contention surrounding almost every point he makes is perhaps the most telling sign that Descartes has failed to produce a wholly persuasive argument through the method of doubt.
The question of whether the Cogito is indubitable, and if so, whether it provides an �Archimidean point� from which Descartes can build a bridge to God or the external world is too complex to approach here. However, it certainly seems as though Descartes has found one of the few propositions which, given �perfect transparency of mind�, could have an element of indubitability. However, perhaps Descartes� greatest mistake is in failing to realise that if the evil demon is powerful enough to gnaw at the axioms of mathematics, then any edifice built in its shadow is suspect.
The Cogito does bring up a rather modern issue though, which
is the problem of language. The subtleties of expressing, in language, the
logic and limitations of expression in language is enough to send anyone into
swirls of self-doubt. However, these niceties become critical when considering
whether existence is a predicate, or the cogito is a syllogism, for instance.
The project of doubt in principle would seem to be worth
pursuing, and indeed is often applied under different guises, but Descartes�
use of it in the Meditations seems to fall on so many grounds that he has
failed to produce the single truth that he sought. However, his work is still
invigorating for its confidence in our ability to access truth and its
tantalising progress in one direction out of �the deep whirlpool of
uncertainty�.