Solipsism ends in meaninglessness

The cluster of arguments - generally referred to as "the private language argument" - that we find in the Investigations against this assumption effectively administers the coup de grâce to both Cartesian dualism and solipsism. (I. § 202; 242-315).

Wittgenstein offers a comprehensive critique of this view. He attacks the notion that experience is necessarily private. His arguments against this are complex, if highly compressed and rather oracular. (For more detailed accounts, cf. Kenny, A., Malcolm, N. (b), Vohra, A.).

Wittgenstein distinguishes two senses of the word "private" as it is normally used: privacy of knowledge and privacy of possession. Something is private to me in the first sense if only I can know it; it is private to me in the second sense if only I can have it. Thus the thesis that experience is necessarily private can mean one of two things, which are not always discriminated from each other with sufficient care: (a) only I can know my experiences or (b) only I can have my experiences. Wittgenstein argues that the first of these is false and the second is true in a sense that does not make experience necessarily private, as follows:

Under (a), if we take pain as an experiential exemplar, we find that the assertion "Only I can know my pains" is a conjunction of two separate theses: (i) I (can) know that I am in pain when I am in pain and (ii) other people cannot know that I am in pain when I am in pain. Thesis (i) is, literally, nonsense: it cannot be meaningfully asserted of me that I know that I am in pain. Wittgenstein's point here is not that I do not know that I am in pain when I am in pain, but rather that the word "know" cannot be significantly employed in this way. (Investigations, I. § 246; II. xi. p. 222). This is because the verbal locution "I am in pain" is usually (though not invariably) an expression of pain - as part of acquired pain-behavior it is a linguistic substitute for such natural expressions of pain as groaning. (I. § 244). For this reason it cannot be governed by an epistemic operator. The prepositional function "I know that x" does not yield a meaningful proposition if the variable is replaced by an expression of pain, linguistic or otherwise. Thus to say that others learn of my pains only from my behavior is misleading, because it suggests that I learn of them otherwise, whereas I don't learn of them at all - I have them. (I. § 246).

Thesis (ii) - other people cannot know that I am in pain when I am in pain - is false. If we take the word "know" is as it is normally used, then it is true to say that other people can and very frequently do know when I am in pain. Indeed, in cases where the pain is extreme, it is often impossible to prevent others from knowing this even when one wishes to do so. Thus, in certain circumstances, it would not be unusual to hear it remarked of someone, for example, that "a moan of pain escaped him" - indicating that despite his efforts, he could not but manifest his pain to others. It thus transpires that neither thesis (i) nor (ii) is true.

If we turn to (b), we find that "Only I can have my pains" expresses a truth, but it is a truth that is grammatical rather than ontological. It draws our attention to the grammatical connection between the personal pronoun "I" and the possessive "my." However, it tells us nothing specifically about pains or other experiences, for it remains true if we replace the word "pains" with many other plural nouns (e.g. "Only I can have my blushes"). Another person can have the same pain as me. If our pains have the same phenomenal characteristics and corresponding locations, we will quite correctly be said to have "the same pain." This is what the expression "the same pain" means. Another person, however, cannot have my pains. My pains are the ones that, if they are expressed at all, are expressed by me. But by exactly the same (grammatical) token, another person cannot have my blushes, sneezes, frowns, fears, and so forth., and none of this can be taken as adding to our stockpile of metaphysical truths. It is true that I may deliberately and successfully keep an experience to myself, in which case that particular experience might be said to be private to me. But I might do this by articulating it in a language that those with whom I was conversing do not understand. There is clearly nothing occult or mysterious about this kind of privacy. (Investigations, II. xi, p. 222). Similarly, experience that I do not or cannot keep to myself is not private. In short, some experiences are private and some are not. Even though some experiences are private in this sense, it does not follow that all experiences could be private. As Wittgenstein points out, "What sometimes happens could always happen" is a fallacy. It does not follow from the fact that some orders are not obeyed that all orders might never be obeyed. For in that case the concept "order" would become incapable of instantiation and would lose its significance. (I. § 345).

With the belief in the essential privacy of experience eliminated as false, the last presupposition underlying solipsism is removed and solipsism is shown as foundationless, in theory and in fact. One might even say, solipsism is necessarily foundationless, for to make an appeal to logical rules or empirical evidence the solipsist would implicitly have to affirm the very thing that he purportedly refuses to believe: the reality of intersubjectively valid criteria and a public, extra-mental world. There is a temptation to say that solipsism is a false philosophical theory, but this is not quite strong or accurate enough. ]As a theory, it is incoherent. What makes it incoherent, above all else, is that the solipsist requires a language (that is a sign-system) to think or to affirm his solipsistic thoughts at all. Given this, it is scarcely surprising that those philosophers who accept the Cartesian premises that make solipsism apparently plausible, if not inescapable, have also invariably assumed that language-usage is itself essentially private. The cluster of arguments - generally referred to as "the private language argument" - that we find in the Investigations against this assumption effectively administers the coup de grâce to both Cartesian dualism and solipsism. (I. § 202; 242-315). Language is an irreducibly public form of life that is encountered in specifically social contexts. Each natural language-system contains an indefinitely large number of "language-games," governed by rules that, though conventional, are not arbitrary personal fiats. The meaning of a word is its (publicly accessible) use in a language. To question, argue, or doubt is to utilize language in a particular way. It is to play a particular kind of public language-game. The proposition "I am the only mind that exists" makes sense only to the extent that it is expressed in a public language, and the existence of such language itself implies the existence of a social context. Such a context exists for the hypothetical last survivor of a nuclear holocaust, but not for the solipsist. A non-linguistic solipsism is unthinkable and a thinkable solipsism is necessarily linguistic. Solipsism therefore presupposes the very thing that it seeks to deny. That solipsistic thoughts are thinkable in the first instance implies the existence of the public, shared, intersubjective world that they purport to call into question.