Course Notes

(3) Cogito Ergo Sum


 (A) Descartes’ First Principle

There are three main passages where Descartes enunciates his ‘first principle’:

(a) . . . I noticed that while I was trying . . . to think everything false, it was necessary that I, who was thinking this, was something. And observing that this truth ‘I am thinking, therefore I exist’ was so firm and sure that all the most extravagant suppositions of the sceptics were incapable of shaking it, I decided that I could accept it without scruple as the first principle of the philosophy I was seeking. [Discourse IV, para. 1; CSM, I, p. 127.]

(b) But [on the most radical sceptical hypothesis] there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind. [Meditations II, para. 3; CSM, II, p. 17.]

(c) . . . we cannot for all that [we might doubt] suppose that we, who are having such thoughts, are nothing. For it is a contradiction to suppose that what thinks does not, at the very time when it is thinking, exist. Accordingly, this piece of knowledge - I am thinking, therefore I exist – is the first and most certain of all to occur to anyone who philosophizes in an orderly way. [Principles I, section 7; CSM, I, pp. 194-5.]


 (B) Interpretations and Issues

(1) Intuition or deduction?

The famous proposition ‘Cogito ergo sum’ does not occur in the Meditations passage, suggesting that it is not, at least, a straightforward inference. Descartes himself denies that it is a syllogism (with a suppressed premiss):

  • When someone says ‘I am thinking, therefore I am, or I exist’, he does not deduce existence from thought by means of a syllogism, but recognizes it as something self-evident by a simple intuition of the mind. This is clear from the fact that if he were deducing it by means of a syllogism, he would have to have had previous knowledge of the major premiss ‘Everything which thinks is, or exists’; yet in fact he learns it from experiencing in his own case that it is impossible that he should think without existing. It is in the nature of our mind to construct general propositions on the basis of our knowledge of particular ones. [2nd Replies, 3rd point; CSM, II, p. 100.]
  • Yet there is clearly some argument involved, ‘I exist’ being some kind of conclusion, arrived at as a result of Descartes’ sceptical considerations. By ‘intuition’ here, Descartes doesn’t just mean a ‘recognition of something as true’, but a ‘recognition of something as certain’; so that we can say that what is being intuited is the certainty of one’s own existence, on the basis of the sceptical argumentation.


    (2) Implicit knowledge

    The passage from the 2nd Replies also raises a problem about the role of general principles. Elsewhere, Descartes states:

  • Before this inference, ‘I am thinking, therefore I exist’, the major ‘whatever thinks exists’ can be known; for it is in reality prior to my inference, and my inference depends on it. This is why the author says in the Principles [CSM, I, pp. 195f.] that the major premiss comes first, namely because implicitly it is always presupposed and prior. But it does not follow that I am always expressly and explicitly aware of its priority, or that I know it before my inference. This is because I am attending only to what I experience inside myself – for example, ‘I am thinking, therefore I exist’. I do not pay attention in the same way to the general notion ‘whatever thinks exists’. As I have explained before, we do not separate out these general propositions from the particular instances; rather, it is in the particular instances that we think of them. This, then, is the sense in which the words cited here should be taken. [Conversation with Burman; CSM, III, p. 333.]
  • Descartes is not denying that, in some sense, we ‘know’ the general principle; what he wants to argue is that it is not our knowledge of this that makes us certain of our own existence. However, there does seem to be a tension between this view and the implications of Descartes’ initial sceptical considerations, where it seems to be suggested that such general propositions can indeed be doubted. Such a view also seems in conflict with the transparency doctrine noted below.


    (3) What kind of thinking?

    ‘Thinking’, according to Descartes, covers any kind of mental activity, so would any kind of thought do as a premiss for the Cogito? There are passages that seem to suggest this, a view that emerges naturally out of his so-called ‘doctrine of the perfect transparency of the mind’, ‘thoughts’ being whatever we are aware of as happening within us (see Principles, I, 9). But this seems to make the emergence of the Cogito conclusion out of the sceptical considerations problematic, it being the specific process of doubting that makes us certain of our own existence. There may thus again be a certain tension between proving the truth of the Cogito conclusion, and demonstrating its certainty.


    (4) Inference or performance?

    Hintikka has argued that there are two lines of thought involved in the Cogito. The first amounts to an inference that I exist from the premisses that if I am right in thinking something, I must exist, and that if I am wrong in thinking something, I must still nevertheless exist (to be wrong). But, he writes:

  • This neat argument is a petitio principii, however, as you may perhaps see by comparing it with the following similar argument: Homer was either a Greek or a barbarian. If he was a Greek, he must have existed; for how could one be a Greek without existing? But if he was a barbarian, he likewise must have existed. Hence he must have existed in any case. [Hintikka, 1962, in Doney, pp. 114-5.]
  • However, it is open to us to simply deny the initial premiss of this argument (if there was no Homer, the premiss is neither true nor false); and to the general charge of petitio principii, Descartes might respond that he is making explicit our knowledge of our own existence, so that we can be certain of it.

    On Hintikka’s second interpretation, the Cogito is construed as a performance, the very act of thinking that I exist (or wondering whether I exist) demonstrating its truth. It is the ‘existential self-verifiability’ of ‘I exist’ that provides the required indubitability when I follow the Cogito line of thought (cf. ibid., pp. 121-2). However, it is hard to reconcile this interpretation with Descartes’ texts. In particular, it is not the thought that I exist that is pivotal in his reasoning, and the relationship to his sceptical considerations is rendered unclear.


    (5) What am I?

    If ‘Cogito ergo sum’ is some kind of argument, then ‘Cogito’ is its premiss. But what exactly does this involve? It has often been argued that all Descartes is entitled to is the premiss ‘there is some thinking going on’. Lichtenberg, for example, wrote: ‘We should say it thinks, just as we say it lightens. To say cogito is already to say too much as soon as we translate it I think. To assume, to postulate the I is a practical requirement.’ [Aphorisms, tr. R.J. Hollingdale, Penguin, 1990, p. 168.] To conclude ‘I am’, then, might seem of little content; yet Descartes wants to move from ‘Cogito ergo sum’ immediately to ‘Sum res cogitans’, which arguably provides a significant addition to ‘Sum’. Here the move is supported by appeal to the principle ‘nihili nulla sunt attributa’ (‘nothing can be predicated of nothing’; cf. e.g. Principles, I, 11), resting on the Aristotelian doctrine of substance and attribute. If there is a thought, then there must be a thinker having it. But what is it to be a thinker?


    Mike Beaney

    October 1998

    Early Modern Philosophy

    Mike Beaney