The theorem that some concepts are unthinkable if they can not be expressed in any of the languages known to the thinker.
This is far from a complete description of this concept but much of it is expressed in the book NineteenEightyFour and in the SapirWhorfHypothesis.
The phrasing above is sufficiently specific as to be falsifiable, unlike many attempted versions of the SapirWhorfHypothesis, and in fact is clearly absolutely false, as demonstrated by the many patients with brain damage in all areas related to understanding and producing language (primarily Wernicke's area, Broca's area, and the fibers interconnecting the two). Despite having no language whatsoever, many of them demonstrate otherwise perfectly normal cognitive abilities according to all tests.
I also don't see why this is a standalone page rather than being folded into SapirWhorfHypothesis. -- DougMerritt
Well, for one thing, if it had been classified under SapirWhorfHypothesis, I would never have found it.
See: Thinking with other than words: