The author conceives of the issue of change in language in adolescence as the working of that mutative dimension of which the entire pubertary process is an expression. The destitution which can at any moment seize upon a word attest to the lack which is consubstantial with any language. The research carried out by the adolescent consists of unveiling this signifying lyingwhile assuring himself of the permanence of the register of language. This « work » would be more generally inscribed in that regime of proof of which other people, more than ever, remain the guarantors. It is by the other that the address and its reception would be assured of a kind of permanence, despite the signifying lack.