Descartes� eagerness to establish the veracity of the Cogito is understandable. It forms the founding-stone of the Cartesian system of knowledge, providing his sought-for Archimedean point. Rejecting or undermining it would have enormous ramifications for any further conclusions he draws. On the other hand, if it were deemed solid, it could also provide a starting-point for other first-person epistemological systems, independent of the conclusions Descartes draws afterwards.
But many commentators attribute greater importance and influence to the Cogito in other respects. At the very least, it holds out the promise of an elegant route leading at least as far as from utter greyness to sollipsism, even though that path has proved to be fraught with complications. Others point to an �intellectual shift�, as the last three hundred years have been dominated by epistemological questions based on a first-person perspective.
The Cogito evolves through the Discourse, Meditations and Principles, taking various formulations: notably �I am thinking, therefore I exist�, and that �the proposition, �I am, I exist�� is necessarily true whenever it is put forward by me or conceived in my mind�. Both specify its truth within a specific time-frame, i.e. for �so long as I think that I am something�. Consequently, a continuous present tense (�I am Xing�) is the most appropriate way to translate the Cogito, and this is what is assumed to be meant by the title. That the Cogito provides fleeting rather than timeless certainty has complicated attempts at logical formalisation.
Descartes treats the Cogito as a revelatory beacon of certainty, immune to the wiles of the evil demon. Initially, it may not be apparent why this should be so. According to him, the Cogito�s peculiarity lies in being self-evidenced and immediately intuitable. In order to gauge the effectiveness of the Cogito against scepticism and determine its uniqueness, we can try altering its emphasis from an act of cognition to a mundane corporeal act, like walking. After all, �I walk, therefore I exist� retains the original form of the Cogito. Does it similarly guarantee the walker�s existence?
Descartes believes the truth of the Cogito to be blindingly obvious (�Everyone can mentally intuit that he exists�), because it is actually self-verifying. Unfortunately, two interpretations of the Cogito can be made, distinguished as being narrow or broad in the scope of their definition of �thinking�.
Under the narrow interpretation, the Cogito�s certainty stems from the fact that all reasons for doubting the Cogito entail that it is true. For after all, doubting is just a special case of thinking, so by doubting that you are thinking, you are necessarily thinking, and so existing. Though this may seem straightforward, it does unwittingly assume that mind is completely and immediately aware of its own activity. Having this doctrine of the �perfect transparency of mind� forestalls the evil demon from implanting a thought labelled �Doubting thinking� in our cognitive apparatus. Otherwise, we would be trapped in the headache of doubting whether we were doubting, even though as far as we were aware, we seemed to be, and so on. Perhaps the doctrine can be defended along the lines that, in contrast to extensible matter, mind is indivisible, so one portion cannot harbour a thought secretly. However, Descartes also considers that dreams could be sense-perceptions originating in the mind involuntarily � this seems incongruous with perfect transparency.
However, Descartes includes a broader variety of cognitive processes under the umbrella of �thinking�, such as affirming, denying, loving, hating, willing and having sense-perceptions. If we were granted immediate awareness of all these different types of thought, an element of intellectual reflection would be introduced. Thus, as before, it would be impossible to doubt that we are hoping/willing/loving, since they all involve reflection, as does doubting.
In this way, because the sensation of walking would be considered a form of thought, one could postulate �I have the sensation of walking, therefore I exist�, with the same weight as the Cogito. However, the actual movement of our body usually implied by this or any other sensation is still stranded with our corporeal, external-world bodies. In the chronology of the Meditations, we cannot yet lay claim to these bodies or be sure that they are as our sense-perceptions depict them, so we can certainly doubt walking without ourselves or the walker necessarily existing.
Having established why the Cogito appears self-verifying while other propositions of identical form are not, it remains to decide whether Descartes is� entitled to describe himself in the first person as a �thinking thing�.
There is certainly a problem here. Although it may be that there is thought taking place, should we so quickly ascribe it to a substance which thinks. After all, the body is clearly delineated, but what delineates or encloses the thoughts involved in the Cogito as being Descartes�? Again, we could return to the unjustified notion of �indivisibility of mind�, whose sanctity thoughts impinge upon, as though from outside. Do we have any greater control or claim to mental events than we do to the sense perceptions we ascribe to external objects, or more importantly, our physical bodies? And yet it is our minds, or more accurately these thoughts, which Descartes claims immediate awareness of.
Descartes� discussion of the wax, and his treatment of himself as a �thinking thing� demonstrates a view of objects as having a �substrata� to which their properties belong. It is this underlying substance which is inferred when the properties of the wax change as it melts, yet our conception of it remains. By extension, we are thinking things � we think thoughts. The alternative �bundle� model describes objects purely as a collection (or bundle) of their properties. Our minds then, are the thoughts which make them up.
In order to be able to say that I think and I exist, Descartes has to establish that without a thinker, there can be no thought. Yet there seems little way that he can move from �thought is taking place� to say that �I am thinking�. Perhaps it could be argued that certainty requires agency � �I am certain that I am thinking� cannot be so easily reduced to �there is certainty that there is thought�. But this is not his argument � he repeatedly claims immediate awareness of his thoughts, which may be his mistake. Not only is this highly suspect, but it makes it difficult to see how thoughts about thoughts can ever arise, one possible hallmark of an agent. Of course, the question of where thoughts ulimately come from may be unanswerable.
A great deal of controversy surrounds the way in which the Cogito is posed. Grammatically, it looks like a premise followed by a conclusion (with another premise concealed). However, Descartes insists that this is not quite the case. Using the terminology of the earlier Rules, he draws a distinction between starting propositions which can be immediately intuited and truth deduced through processes of inference. In explanation, Descartes could be seen as intuiting �perfect transparency of mind� as a concealed premise, intuiting that he is thinking, immediately inferring that he exists (incorporating Williams� suggestion that the missing major premise is first conceived as being non-existential), and finally inducing the existential major premise �whatever thinks, exists� from there. Although far more can be said on this issue, Descartes� confusing descriptions of how the Cogito is both intuitable and rationalisable afterwards should not be seen as a serious problem.
Other commentators have attacted the Cogito as being trivial, saying little more than �I exist, therefore I exist�. In a way this is true if one accepts the need for some sort of very general non-existential major premise, but this simply shifts the burden of doubt back one level. Although it is obvious in one sense that by asserting our existence we must exist, Descartes tries to frame this in a satisfyingly incontrovertible fashion. Unfortunately, the pre-suppositions and �linguistic intuitions� which perhaps need to be made to make any progress from the method of doubt hamstring the attempt. It does seem that the arguments are strong for thoughts existing in some form, but Descartes is unconvincing with regard to concrete certainty in our own existence. However, the Cogito does seem to apply to a wider sense of �thinking� than might have been expected, including the sensation of walking, even if not the actual corporeal act.