Do the formal languages of logic share so many properties with natural languages that it would be nonsense to separate them in more advanced investigations or, on the contrary, are formal languages a sort of ‘crystalline form’ of natural languages so that any further logical investigation into their structure is useless? On the other hand, is it true that humans think in natural languages or rather in a kind of internal ‘language’ (code)? In either of these cases, is it possible to model the processing of natural language information using formal languages or is such modelling useless and we should instead wait until the plausible internal ‘language’ (code) is confirmed and its nature revealed?
The above questions concern therefore the following possibly triangular relationship: (1) formal (symbolic) language vs. natural language, (2) natural language vs. internal ‘language’ (code) and (3) internal ‘language’ (code) vs. formal (symbolic) language. There are different opinions regarding these questions. Let me quote three of them: (1) for some linguists, for whom “language is thought”, there should probably be no room for the hypothesis of two different languages such as the internal ‘language’ (code) and the natural language, (2) for some logicians, natural languages are, in fact, “as formal languages”, (3) for some neurologists, there should exist a “code” in the human brain but we do not yet know what its nature is.