Can I Prove that I Exist?

Can I Prove that I Exist?

The Cogito purports to be a proof that I exist. It is supposed to establish the proposition that I exist. But this is a funny kind of proof for a simple reason: it only proves my existence to me. I cannot use it to prove my existence to you, or to any other person no matter how intelligent and receptive to rational argument. If I come up to you and announce “I can prove my existence” and offer “I think, therefore I am”, you will reply “But how do I know that you think?” My alleged proof fails at the first hurdle: I have not established its basic premise. The problem of other minds prevents the proof from working. I cannot prove to anyone else that I exist, only to myself. What kind of proof is that? Is it really a proof at all? The OED gives us “demonstrate by evidence or argument the truth or existence of” for “prove”, and goes on to link the concept to proof under the law. You can’t go into a court of law and propose to prove the existence of someone or something by establishing its existence for you—and you alone. That’s not a legal proof. The proof has to be public not private. Would there be any proofs of anything if all such proofs were irremediably private in this way? More fundamentally, does it even make sense to qualify “proof” by “to me”—doesn’t that take back with one hand what has been offered by the other? It’s like saying you have evidence for something and then adding that it’s only evidence for you. In the Cogito the putative evidence is necessarily available only to the proponent of the proof—in his acts of thinking. It is impossible to accept the proof for anyone but the individual giving it. The audience will retort, “But that’s no proof to me!” You can’t relativize proof in that way. A proof that only I can accept is no kind of proof at all.

It is the same in science and mathematics. You couldn’t go to a scientific conference claiming to have a proof of something and then turn around and say the proof is only available to yourself. You couldn’t base a science, say physics, on a proposition whose truth is ascertainable only by you. As Wittgenstein would say, the word “proof” has its meaning in a language game involving other people and what they can know; you can’t detach it from this language game and expect to retain sense. The idea of a “private proof” is a contradiction. You may be convinced of the truth of “I exist” by reflection on the Cogito, but you are misusing language if you say you have a proof of this proposition. And isn’t it very strange to describe yourself as having proved that you exist by means of the Cogito? Maybe you know it thereby, but you haven’t found a proof of it—not in any ordinary sense. But it sounds scientific and rigorous to speak of proof in this connection—as if we are talking about Euclidian geometry or Newtonian physics or Darwinian biology. In these subjects the proofs are all objective and public, but not in the case of the Cogito. For the “proof” is limited to a single individual, necessarily so. If my science requires that other people exist, the Cogito is no use in establishing this. The science becomes limited to me, which disqualifies it from being a science. Only I can have reason to believe this alleged science if it rests on my employment of the Cogito. This kind of certainty is no use to science—or law or everyday life. It is really a kind of category mistake to call the Cogito a proof, no matter cogent it otherwise may be. Nor is it right to characterize it as an argument or a presentation of evidence: these concepts presuppose a social context, i.e., interpersonal accessibility. The words in question have a meaning that derives from their use in social contexts; they are misused if detached from such a context. At the very least it should be signaled that the Cogito doesn’t work to prove one’s existence to other people, unlike other proofs of existence. Clarity is best served by withholding that term from discussions of the Cogito.[1]

[1] If someone seriously doubts that I exist as a thinking thing, it cuts absolutely no ice to reply, “But I can prove that I exist”, proceeding to offer the Cogito. The skeptic will simply say, “Your initial premise begs the question”. The Cogito is no use at all if other people question your existence.