The doctoral thesis deals with transitivity alternations in contemporary French which are not morphologically marked, particularly with the relationship between conventional and non-conventional use. The study is based on a corpus of non-conventional uses of verbs, that is, verbs that are claimed to be intransitive appearing with objects and transitive verbs being used without objects. The corpus consists of sentences collected one by one mainly from magazines and detective novels, where the language is not intended to be as normative as often in French written texts. The theoretical basis is functional; the linguistic material to be analysed is seen as inseparable from its use. The aim of the study is to detect the productive transitivity alternations available in contemporary French: which are the possibilities of verbs to appear in different actancy schemata? Three main cases are distinguished. In non-conventional use the relationship between the referent of the subject and the referent of the verb may be the same as in conventional use. In the first case, the object is absent and its implicit referent may be latent or generic. It is claimed that every verb may appear with a latent or a generic object if the context is appropriate. The second case consists of uses with objects. The indefiniteness of semantic implications of the function object is illustrated. If a conventionally intransitive verb is used with an object, its referent is often an effected one. Another common phenomenon is that the preposition introducing a complement is dropped out. Many of the constructions with objects do have transitive semantics. In the third case the intransitive subject corresponds to the object of the transitive construction. Such verbs are often called labile. It is claimed that there are no labile verbs, but labile uses in contemporary French.