French prepositions figure as obligatory markers of syntactic functions, verbalize semantic oppositions, and are an ingredient of complex expressions that are sometimes all but indistinguishable from free syntagmas. Proceeding from the classification problems posed by these facts, the study proposes new generative approaches and integrates them into a framework defined in terms of grammaticalization theory. The aim is to achieve an accurate model of the transitions between P (preposition) and neighbouring lexical categories on the one hand, and between P and the functional category K (case marker) on the other.