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Cogito ergo sum



Descartes claims that the experience of self-consciousness constitutes the certain epistemological foundation he had been seeking by means of methodical doubt. This experience--certain, indubitable, and logically necessary according to Descartes--is concisely expressed in the famous Latin formulation, Cogito ergo sum: “I think, therefore I am.” However, Descartes offered several formulations of the Cogito that are instructive for interpreting its precise meaning.

1. Discourse on Method (1637): Part IV

But immediately I noticed that while I was trying thus 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 skeptics were incapable of shaking it, I decided that I could accept it without scruple as the first principle of the philosophy I was seeking.

2. Mediations on First Philosophy (1641): Meditation II

Does it now follow that I too do not exist? No: if I convinced myself of something then I certainty existed. But 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, but he will never bring it about that I am nothing, so long as I think I am something... So 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.

3. Principles of Philosophy (1644): Part I, 7

It is not possible for us to doubt that we exist while we are doubting; and this is the first thing we come to know when we philosophize in an orderly way.

In rejecting—and even imagining to be false—everything which we can in any way doubt, it is easy for us to suppose that there is no God and no heaven, and that there are no bodies, and even that we ourselves have no hands or feet, or indeed any body at all. But we cannot for all that 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.


1. What is meant by “thought.” (PP I: 9)

2. The Cogito as first truth in the order of knowledge, i.e., as epistemic foundation for philosophy and sciences. It is not, however, first in the order of being (reality); a distinction Descartes accords to God (Meditation III).

3. The Cogito (the mediator’s certainty of his own existence) emerges as a direct result of the systematic process of doubt (philosophizing in an orderly way) described in Meditation I, and in particular, from the extreme scenario of a supremely powerful deceiver (malicious demon or evil genius). As such, the very act of radically doubting my existence, for Descartes, actually confirms it.

4. Certainty of one’s own existence: The qualifying clause in the Meditations’ formulation (... whenever it is put forward by me or conceived in my mind) is significant for an accurate conception of Cartesian certainty. The certainty of my existence generated by the Cogito is not like the certainty of some timeless, necessary truth of logic or mathematics. In general, my existence is not necessary in any sense. But so long as I am actually engaged in the process of thinking, I must exist. Hence, the certainty of the Cogito is temporally relative to the performative process of thinking (in the present tense: I am thinking).

5. The meaning of “therefore” (ergo) or the link between “I am thinking” and “I exist.”

a) Logical inference resulting in a deductive syllogism:

            1. Everything that thinks exists (unstated premise)
            2. I am thinking                                                   
            3. Therefore, I exist

b) Performative implication: the certainty of my existence is not discovered on the basis of a general, formal, syllogistic piece of reasoning. Rather, it is pragmatically implied by the act of thinking on the part of the individual mediator, who “recognizes in his own particular case that it is impossible that he should think without existing.” As such, the activity of thinking presupposes existence as its necessary condition of possibility. One’s own existence becomes self-evident through the act of thinking.

6. Objection: Is Descartes’ methodic doubt, despite its extravagant devices, as radical as he claims? Does the Cogito contain any assumptions which, to be consistent with radical doubt, should be suspended and as such unavailable for use? In other words, is the Cogito a genuinely presuppositionless starting point upon which to found all consequent knowledge?