Habitability

A “habitable” language is one in which its users can express themselves without straying over the language's boundaries into unallowed sentences. If meant only to permit expressions addressed to a restricted subject matter, such a language can be a proper subset of, for example, the set of English sentences. Such a habitable subset is what any practical English man—computer interface must be. Yet, for any subject matter of interest, a subset that contains all English sentences “appropriate” to that subject will be impossibly large. Moreover, the subset must consist of the utterances of performance, not the sentences of competence; and, besides having differences of form, utterances are partly interpreted and disambiguated on the basis of the situation of usage. Thus the “English subset” must be redefined to bear the less direct relationship to the grammar that its performative nature indicates, and then, because of the large size of this subset, it must be greatly reduced, though without losing habitability.