This dissertation presents a description of some French sentential constructions introduced by the non-causal adverb ‘comme’ (translated by as or like in English). First, we analyze their syntactic, lexical and semantic properties and then we give an HPSG account of our analyses (Pollard et Sag 1994, Sag 1997). We show that they share common categorial, structural and semantic properties: comme clauses are adjuncts and a type of free relative clause that contains the extraction of a manner adverb. Comme as an adverbial Wh word, is the filler of an unbounded dependency. The whole adjunct phrase has a predicative relation, its semantics is construed through the semantics of the extracted adverbial argument. This semantics is always an equivalence-like relation that takes two elements. We observed two distributions of comme clauses regarding their semantics: either they are modifier adjuncts–they modify the lexical head of a V/VP, A/AP, N/NP–or, they are parenthetical adjuncts–they select for an S. Three uses are noted: the report of a speech act––the report of a speech, of an order or, of a question: this construction is called Reportive–, an analogy between two propositions (Analogie Comme adjuncts), an equivalence of property between two predicates, two properties or two nouns (Manner Modifier adjuncts); an examination of their linear properties, lexical restrictions and syntactic constraints is given. In addition, the dissertation draws up a general classification for non-canonical arguments (extracted arguments, propositional and predicative anaphors, ellipses, gapping) that regularly occur within comme clauses. Our contribution to HSPG grammar is the following : we give an account for the distinction between modifier vs. parenthetical adjuncts; our constraint-based analysis proposes a treatment for adverbial extraction in free relative clauses, and enriches the typology of non-canonical arguments. We integrate the set of comme constructions in a typed hierarchy.