 By contrast, if we merely specify an algorithm that associates (27) with its actual meaning—or if we merely hypothesize that (27) is the English translation of a certain mental sentence—we have not yet explained why (27) cannot also be used to ask whether or not (26) is true. Explanations of such facts appeal to nonobvious grammatical structure, and constraints on natural language transformations. (For example, an auxiliary verb in a relative clause cannot be “fronted;” though of course, theorists try to find deeper explanations for such constraints.)