What is the cogito ergo sum?

René Descartes, answered from the texts and cited to the page.

René Descartes answers

The proposition cogito ergo sum — I think, therefore I am — is the first and most certain truth that survives the full force of methodical doubt. When I had supposed all things false, dismissed the testimony of my senses, and imagined even that my memory might be entirely deceptive, one thing remained that I could not dismiss: the very act of thinking that all this was false required that I, who thought it, should exist.1

Let the most powerful deceiver do his worst; let him employ all his ingenuity in deceiving me — he can never bring it about that I am nothing so long as I think that I am something.2 The proposition I am, I exist is necessarily true each time I pronounce it or mentally conceive it.3 It is not a syllogism. Those who have objected that I must have silently presupposed the major premise — whatever thinks, exists — and that I therefore smuggled in a prejudice before the argument began, misunderstand the method by which truth is actually discovered.4

We do not first grasp universal propositions and then deduce particular truths from them, as in the order of dialectical syllogism; on the contrary, it is in particular instances that we think of these general notions, not separately from them.5 The cogito is reached by attending only to what I experience within myself — I am thinking, therefore I exist — without expressly adverting to the general principle, which is nonetheless implicitly presupposed and prior.6

The knowledge is immediate: a primary notion, not derived by means of any syllogism.7 What follows from this first certainty is equally important. Examining attentively what I was, I saw that I could conceive myself as having no body, no world, no place — and yet I could not conceive that I was not.8 From the very fact that I thought of doubting the truth of other things, it followed evidently that I was; had I ceased from thinking entirely, I should have had no reason to suppose I had existed at all.9

This is how I knew that I was a substance whose whole essence or nature is to think, requiring no place and depending on no material thing — the res cogitans, more easily known than any body, and entirely distinct from it.10 From this single indubitable instance I also drew the general rule: whatever we conceive very clearly and distinctly is true.11

The cogito is not merely a foundation; it is the model of all certain knowledge, showing in one particular case what clara et distincta perceptio — clear and distinct perception — actually is.

Sources

  1. I suppose, then, that all the things that I see are false; I persuade myself that nothing has ever existed of all that my fallacious memory represents to me... was I not then likewise persuaded that I did not exist? Not at all; of a surety I myself did exist since I persuaded myself of something.
    The Philosophical Works of Descartes Vol I
  2. But there is some deceiver or other, very powerful and very cunning, who ever employs his ingenuity in deceiving me. Then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something.
    The Philosophical Works of Descartes Vol I
  3. we must come to the definite conclusion that this proposition: I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.
    The Philosophical Works of Descartes Vol I
  4. the greater error here is our critic's assumption that the knowledge of particular truths is always deduced from universal propositions in consonance with the order of the sequence observed in the syllogism of dialectic.
    The Philosophical Works of Descartes Vol II - Objections and Replies
  5. we do not separate out these general propositions from the particular instances; rather, it is in the particular instances that we think of them.
    The Philosophical Writings of Descartes Vol III, The Correspondence, pp. 348–349
  6. I am attending only to what I experience within 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'.
    The Philosophical Writings of Descartes Vol III, The Correspondence, pp. 348–349
  7. When we become aware that we are thinking beings, this is a primary notion, which is not derived by means of any syllogism.
    The Philosophical Writings of Descartes Vol III, The Correspondence, pp. 348–349
  8. I saw that I could conceive that I had no body, and that there was no world nor place where I might be; but yet that I could not for all that conceive that I was not.
    The Philosophical Works of Descartes Vol I
  9. from the very fact that I thought of doubting the truth of other things, it very evidently and certainly followed that I was; on the other hand if I had only ceased from thinking, even if all the rest of what I had ever imagined had really existed, I should have no reason for thinking that I had existed.
    The Philosophical Works of Descartes Vol I
  10. I knew that I was a substance the whole essence or nature of which is to think, and that for its existence there is no need of any place, nor does it depend on any material thing; so that this 'me', that is to say, the soul by which I am what I am, is entirely distinct from body.
    The Philosophical Works of Descartes Vol I
  11. I came to the conclusion that I might assume, as a general rule, that the things which we conceive very clearly and distinctly are all true.
    The Philosophical Works of Descartes Vol I