Tuesday, March 18, 2014

Is Descartes’s Cogito Argument an Example of Necessary a posteriori Truth?

What is the epistemological status of Descartes’s cogito ergo sum (or cogito) argument? That argument and Descartes’s conclusion (I think therefore I am) is reviewed in the video below.

The epistemological status of the cogito ergo sum proposition and the argument underlying it is a difficult philosophical question, and the specialist literature is vast (for just a sample, see Hintikka 1962; Hintikka 1962; Suter 1971; Sarkar 2003; Williams 2005).

Some modern scholars are inclined to think that Descartes understood the cogito insight not as a formal argument per se, but as an intuition or truth from direct introspection, and this finds support in Descartes’s own statement:
“Now awareness of first principles is not normally called ‘knowledge’ by dialectitians. And when we become aware that we are thinking things, this is a primary notion which is not derived by means of any syllogism. 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.” (Descartes, Second Replies).
But intuition or direct introspection should most probably be considered a form of a posteriori knowledge: after all, any conscious thought or perception you have is a form of direct experience.

So the cogito argument is not an a priori syllogistic argument.

But does it have necessary truth? Descartes thought so, and said so in the Meditations:
“… this proposition: I am, I exist, whenever it is uttered from me, or conceived by the mind, necessarily is true.” (Meditation II).
If the justification for the cogito is not a priori, does it show that there are necessary a posteriori truths?

Although modern analytic philosophy, following Saul Kripke, admits the existence of ontologically necessary a posteriori truths, nevertheless the skeptical argument against both the necessary ontological and epistemological truth of the cogito in the form that Descartes proposed it seems convincing.

The crucial problem is Descartes’s claim that an “I’ exists, and that mere conscious experience allows one to infer an existing “I.” The “I” must be understood as a discrete conscious entity and perceiving subject that perceives objects of perception.

But that there is a discrete entity and perceiving subject that we each personally refer to as “I” does not necessarily follow from the cogito, as many skeptics and critics of Descartes have pointed out. What if what exists just consists of thoughts, sensations and perceptions with no discrete, perceiving subjects?

At most, what seems to be certain from direct experience is that kinds of perception, sensation or thinking exist or are occurring, not that any discrete subject exists or is perceiving.

If one takes this as the ultimate inference to be made from direct conscious experience – that kinds of perception, sensation or thinking exist – then perhaps that is a necessary a posteriori truth. Even if one were to concede this, it does not take one very far, however. In fact, Descartes had to prove the existence of god just to reconstruct a new apriorist epistemology, once he had torn down his previous one through the Cartesian method of doubt.

To order to reconstruct a secure Rationalist apriorist epistemology – as opposed to a merely probabilistic inductive one – Descartes needed a miracle, a deus ex machina!

Armstrong, D. M. 1963. “Is Introspective Knowledge Incorrigible?,” The Philosophical Review 72.4: 417–432.

Francks, Richard. 2008. Descartes’ Meditations: A Reader’s Guide. Continuum, London and New York.

Hintikka, Jaakko. 1962. “Cogito, Ergo Sum: Inference or Performance?,” Philosophical Review 71: 3–32.

Hintikka, Jaakko. 1963. “Cogito, Ergo Sum as an Inference and a Performance,” The Philosophical Review 72.4: 487–496.

Lyons, William. 1986. The Disappearance of Introspection. MIT Press, Cambridge, Mass.

Sarkar, Husain. 2003. Descartes’s Cogito: Saved from the Great Shipwreck. Cambridge University Press, Cambridge.

Suter, Ronald. 1971. “Sum is a Logical Consequence of Cogito,” Philosophy and Phenomenological Research 32.2: 235–240.

Williams, Bernard. 2005. Descartes: The Project of Pure Enquiry. Routledge, London.


  1. "But intuition or direct introspection should most probably be considered a form of a posteriori knowledge: after all, any conscious thought or perception you have is a form of direct experience."

    If "any conscious thought" were considered to be a posteriori, would we have defined away the a priori completely? Not just "cogito ergo sum" is a posteriori, but so is "cogito"?

    Is there anything left?

    1. You are right: I went too far by saying "any conscious thought".

      A priori propositions and arguments do indeed exist, as in the standard definitions:

      (1) an analytic proposition is known as true in virtue of the meanings of the words used.

      (2) deductive arguments are known as true a priori if they are logically valid, and if major and minor premises are true by (1).

      If major and minor premises are synthetic a posteriori, however, one will need empirical evidence to prove them.

  2. If I write a fictitious character that proclaims "I think, therefore I am" and name him Descartes, isn't that character in some sort of error by our lights? If that character proclaims that it can reason, isn't that also wrong? Because we are implying a particular type of existence, the commonly held "real world".

    How could the real Descartes know he isn't a fictional character, a simulation, a butterfly's dream, a shadow on the wall of a cave, etc? Mere claims that you think cannot distinguish which sort of existence is present, and with a little ingenuity we could probably find examples such as "a non-existent character in a book said ITTIA." I don't see that as worse nonsense.

    1. Yes, I see the fundamental point here, but to play devil's advocate for Descartes: even if you were a type of fiction (that is, a figure created by the mind of some entity), it must still be creating the thoughts and sensations any person experiences now, even if these are to trick you.

      As Descartes says, even if the evil demon was deceiving me about everything I experience, he cannot fool me about the fact I am having at least some kind of experience (even a deceptive one).