ABSTRACT : In his semiological, semantic and grammatical analyses, Roger Bacon always takes into account the relationship between language's system, signs, utterances and conditions of enunciation. First, in the case of Semiology, signs have an original "imposition", but the speaker is able to "reimpose" them, in a given situation corresponding to a definite state of the world. Second, in the case of Semantics, R.B. gives an original response to the problem of the ambiguity of utterances having one or several logical operators. One possible solution is to make the interpretation depend upon the surface marks of the utterance ; according to a second solution, the interpretation depends upon the "modus proferendi" ; he introduces the "generat...