Did Descartes view "cogito ergo sum" as applying only to himself?

Question

I'm not a philosophical expert, but I'm wondering.

Isn't it contradictory that Descartes, using his cogito, wants to both (a) prove that he exists and is uncertain of others and (b) provides a proof that can enable anyone to prove they exist?

Answer 1

Yes and no. When Descartes was within his argument, he surely viewed "cogito ergo sum" as applying only to himself. At the crucial moment in the argument when he needs the Cogito, he needs it as a sure ground of knowledge. And, at that moment, he did not know whether other people existed. Descartes had come to doubt anything that is learned through the senses. And the existence of other people is surely learned through the senses. So he himself remained the only candidate for "cogito ergo sum".

But I was persuaded that there was nothing in all the world, that there was no heaven, no earth, that there were no minds, nor any bodies: was I not then likewise persuaded that I did not exist? Not at all...(Meditations II)

On the other hand, viewed from without, the Cogito argument is available for any being like Descartes, that is for any intelligent being possessing a mind. And as an author,  Descartes surely expected his readers to repeat his owm reasoning from their own first-person perspectives.

...without however expecting any praise from the vulgar and without the hope that my book will have many readers. On the contrary, I should never advise anyone to read it excepting those who desire to meditate seriously with me, and who can detach their minds from affairs of sense, and deliver themselves entirely from every sort of prejudice. (Meditations Preface to The Reader)

Answer 2

While the Meditations are written in a first person manner, I think he means them to be an investigation of his own consciousness (to use wording that would be foreign to him).

The manner in which he constructs the proof for the self's existence does not hinge at all on any property specific to Rene Descartes. Instead, it's a product of a constructive dilemma:

1. Either the self is or is not deceived.
2. If the self is not deceived, then the self's perception that the self exists is veridical.
3. If the self is deceived, then there must be an existing self to be deceived.
4. Ergo, either the self is correct to believe it exists or the self exists because it is deceived.

Either way a self exists.

Descartes also has a longer form version of this implied at a later point in Meditation 2 that adds a temporal component to the logic. It's "first-personal" but not limited to the person of Descartes.

A place further along where you argument probably has more traction is in Descartes' argument for the existence of God. Here, he maintains that he has an idea of perfect being (i.e. the God of the philosophers), which he claims all people have. It's not nearly as tight as the argument for the self. But Descartes' argument for the self and his argument for God circularly depend on each other (God as a guarantee the self can expect logical consequences and the self as the possessor of the idea God -- see John Cottingham "Cartesian Circle").

When you suggest that there's a "contradiction," I think what you mean is something along these lines:

1. Descartes proves that he exists but * is unsure of the existence of others.
2. Using his proof, any person can prove that they exist but * be unsure of the existence of others).
3. Ergo, all people's existence can be proved but simultaneously * the existence of all people is doubtful.

Here I * the second part of your claim because Descartes only holds this view for a moment.

In the end though, this is not a contradiction. The form of Descartes' argument is asymmetric, it would mean that person D can prove D exists (qua thinking thing) and (at that point) does not yet have a proof for the existence of others (other than D).

The same thing is true of such trivial things as vision -- what I see is not the same as what you see even if we could both be looking at the same object. If, for instance, in my office I see a copy of Hegel's Phenomenology of Spirit but in your office you don't. There's no contradiction -- there's just a difference of perspective.

Descartes proof (restricting ourselves to Meditation 2) is that for any given self, that self can know it exists and does not yet know if other selves exist in the same way. That this can be true of every self is no different than the idea that any self in my office can see my copy of Kierkegaard's Sickness unto Death but no self outside of my office can see it.