This thesis introduces an experimental and quantitative approach to language through the study of the concept of soft constraints and its application to two phenomena of order in French: the position of the attributive adjective and the ordering of verbal complements occurring in postverbal position. Soft constraints are defined as affecting the acceptability rather than the grammaticality of the sentences. Our main hypothesis is that these constraints are properties of the language and thus must studied in syntax. These constraints raise a methodological issue: since they do not affect the grammaticality of the sentences, they cannot be investigated using the traditional tools of syntax (introspection and grammaticality judgment). It is therefore necessary to define tools for their description and analysis. The proposed methods are statistical analysis of corpus date, inspired by the work of Bresnan et al. (2007) and Bresnan & Ford (2010) and, to a lesser extent, psycholinguistic experiment. Regarding the position of the adjective, we test most of the constraints encountered in the literature and we propose a statistical analysis of the data extracted from the French Treebank corpus. We show the importance of the adjectival item and the nominal item with which it combines. Other constraints linked to the internal syntax of the adjectival phrase and the noun phrase also play a significant role in the choice of position. The work on the relative order of the verbal complements is conducted on a sample of sentences extracted from two newspapers corpora (French Treebank and Est-Républicain) and two corpora of spoken French (ESTER and C-ORAL-ROM). We show the significant influence of the constituent weight over the ordering: short before long order which is a feature of SVO languages like French, is observed in over 86% of cases. We also identify the important role of the verbal lemma associated with its semantic class (annotated with the dictionary of Dubois & Dubois-Charlier, 1997). Finally, building on the analysis of corpus data as well a two questionnaires eliciting acceptability judgments, it seems that nor animacy neither information structure (given/new, Prince, 1981) have a significant effect on the postverbal complement ordering.