Private language argument

The private language argument is a family of considerations, developed by Ludwig Wittgenstein in Philosophical Investigations (PI), aiming to show that a language whose expressions are, in principle, understandable by only a single individual is unintelligible. In PI the idea is introduced at §243 and examined chiefly in §§244–271, with related remarks continuing to §315. These remarks are not a single formal proof but a sequence of interlocking moves, examples, and reminders. The central conclusion is commonly put this way: a necessarily private language—one whose meanings are fixed by items only the speaker can access—cannot establish the standards of correct/incorrect use required for meaningful language.

Scholars distinguish Wittgenstein's target from mere ciphers or idiolects: a secret code could in principle be decoded or taught to others, whereas a private language, as defined here, is in principle unlearnable and untranslatable by anyone else. The topic has been central to late 20th-century debates on meaning, mind, rule-following, and the social character of language.