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.