Wittgenstein didn’t come come up with the idea of a “private language” but in his Philosophical Investigations he famously argued that the concept itself is nonsense (not via a single logical “proof” but using several thought experiments).
The idea that a private language exists (ie. ‘mentalese’) is taken for granted by a lot of authors. I recently read Stephen Pinker’s book The Language Instinct and he never seemed to doubt the concept for instance.
The idea that a private language exists (ie. ‘mentalese’) is taken for granted by a lot of authors. I recently read Stephen Pinker’s book The Language Instinct and he never seemed to doubt the concept for instance.