private language argument an argument designed to show that there cannot be a language that only one person can speak – a language that is essentially private, that no one else can in principle understand. In addition to its intrinsic interest, the private language argument is relevant to discussions of linguistic rules and linguistic meaning, behaviorism, solipsism, and phenomenalism. The argument is closely associated with Wittgenstein’s Philosophical Investigations (1958). The exact structure of the argument is controversial; this account should be regarded as a standard one, but not beyond dispute.
The argument begins with the supposition that a person assigns signs to sensations, where these are taken to be private to the person who has them, and attempts to show that this supposition cannot be sustained because no standards for the correct or incorrect application of the same sign to a recurrence of the same sensation are possible. Thus Wittgenstein supposes that he undertakes to keep a diary about the recurrence of a certain sensation; he associates it with the sign ‘S’, and marks ‘S’ on a calendar every day he has that sensation. Wittgenstein finds the nature of the association of the sign and sensation obscure, on the ground that ‘S’ cannot be given an ordinary definition (this would make its meaning publicly accessible) or even an ostensive definition. He further argues that there is no difference between correct and incorrect entries of ‘S’ on subsequent days. The initial sensation with which the sign ‘S’ was associated is no longer present, and so it cannot be compared with a subsequent sensation taken to be of the same kind. He could at best claim to remember the nature of the initial sensation, and judge that it is of the same kind as today’s. But since the memory cannot confirm its own accuracy, there is no possible test of whether he remembers the initial association of sign and sensation right today. Consequently there is no criterion for the correct reapplication of the sign ‘S’. Thus we cannot make sense of the notion of correctly reapplying ‘S’, and cannot make sense of the notion of a private language. The argument described appears to question only the claim that one could have terms for private mental occurrences, and may not seem to impugn a broader notion of a private language whose expressions are not restricted to signs for sensations. Advocates of Wittgenstein’s argument would generalize it and claim that the focus on sensations simply highlights the absence of a distinction between correct and incorrect reapplications of words. A language with terms for publicly accessible objects would, if private to its user, still be claimed to lack criteria for the correct reapplication of such terms. This broader notion of a private language would thus be argued to be equally incoherent. See also PHILOSOPHY OF LANGUAGE , PROB- LEM OF OTHER MINDS , WITTGENSTEI. R.B.