Knowledge

If thinking proves existence, then how can you prove that anyone else exists?

Comments

What you have in mind is Descartes's cogito argument: "Insofar as I am thinking, I must exist." Descartes was trying to systematically rid himself of beliefs in any propositions about which he could conceive of being deceived about. His insight was that no matter how thoroughly he was deceived on any other matter, he couldn't at least be deceived about the fact that he was thinking, since a person cannot be in the state of being deceived without being in some mental state or other. Hence, he concluded, as long as he was thinking (actually, as long as he was experiencing any mental state) he could be completely certain of his own existence.

You're right that this argument can only be made in the first person. Descartes himself had a two-step strategy for demonstrating the existence of other minds: first, he established the general reliability of the senses, and thus established his right to believe in the existence of material objects. So that got him knowledge of other people's bodies. But what about their minds? Here comes the second step (taken in his less wellknown work, Discourse on Method). Descartes argues that human bodies display the capacity for making rationally appropriate responses to an infinite variety of distinct circumstances, a capacity displayed most compellingly in the use of languge. Since bodies -- mere matter -- is limited to responded according to its physical nature, there must, Descartes reasoned, be an immaterial substance, with the capacity to reason, that's responsible for the vast behavioral repertoire of the human body. Descartes bolsters his argument by replying to a couple of objections.

This is a very contemporary kind of argument, the kind that philosophers of science and epistemologists call "inference to the best explanation." It's an empirical argument -- that is, an argument that depends on sense experience (aka "observation"), rather than on pure reason, as the cogito argument does. Noam Chomsky specifically cites Descartes as the inspiration for many of his own arguments for an innate language faculty.

This type of argument -- arguing that the best explanation for some body of observed fact is the existence of a mind -- is probably the best, and maybe the only way to solve the problem of "other minds."

It is worth noting that Descartes' version of this problem is made all the more difficult by the fact that thinking-substance and material-substance were considered to be of radically different types. Accordingly, it is not just the case that access to my thought, and proof of my existence as a mind, are accidentally in the first person, but necessarily so. Thought is not the kind of property that a material object could exhibit.

From this is also follows that if a material object does exhibit clear signs of rational thought, then it could not but contain a mind. If Descartes is able to observe in himself actions of the body that necessarily depend upon thought, he could then looks for such actions in other bodies and thus prove other minds. The problem is proving the necessity of the dependence relation.

However, this notion of two distinct types of substance is by no means universally accepted! If, in some way, thought were a feature of our bodies (of a physical brain, say), then the problem of other minds appears quite different.

Read another response by Louise Antony, Douglas Burnham

Read another response about Knowledge