The private language argument holds that a language that can only be understood by a single individual is incoherent, and in fact not a language. The argument was introduced by Ludwig Wittgenstein in his later works, especially in his Philosophical Investigations . The argument became one of the central themes of philosophy during the second half of the 20th century.
Wittgenstein defined private language as a "language whose words refer to what only its speaker can know - to his immediate private sensations. Therefore, another person cannot understand language," because the elements that define his vocabulary are necessarily inaccessible to others.
The notion of a private language was largely unheard of in philosophy prior to its introduction by Wittgenstein. As soon as he introduced the notion of a private language, Wittgenstein proposed a series of arguments designed to show that such a private language cannot exist. Wittgenstein did not articulate the argument succinctly or linearly. On the contrary, in his Investigations he examined a series of particular uses of language and mathematics, and urged the reader to contemplate the implications of these uses. Because of this, there is considerable controversy both over the nature of the argument and over its length and limitations. For this reason, it is frequent to speak of arguments of private language.
The importance of introducing the notion of a private language and formulating an argument defending its impossibility is that many areas of philosophy depend implicitly on the possibility that such a private language exists.
