This study intends to highlight and explain the development, in the Renaissance, of a category of fictions characterized by their comical improbability and their - more or less serious - claim to convey a philosophical content. Based on a corpus of six Italian and French “philosophical fantasies” (Alberti’s Momus, Ariosto’s Orlando Furioso, Folengo’s Baldo, Rabelais’s works, Ronsard’s “seasonal hymns”, and Philippe d’Alcripe’s Nouvelle Fabrique), our study aims at defining this category, and showing how a fictional pattern, initially borrowed by Italian humanists from Lucian of Samosata, has been adapted to new philosophical stakes and controversies. Our last six chapters are devoted to case studies. The five previous ones explore, from a theoretical perspective, the status of incredible fictions in the horatian, platonic and aristotelian poetics: far from being systematically regarded as lies, or considered as artistic failures, they benefit from the high value granted to fictional invention and to the intellectual impact of astonishment. However, their relationship to the allegorical tradition is complex: while they constantly refer to it, they resist to the allegorizers’s investigation. This ambiguity is specific to the products of creative fantasy which, in Renaissance philosophy, is a strongly ambivalent faculty of the soul. / This study intends to highlight and explain the development, in the Renaissance, of a category of fictions characterized by their comical improbability and their - more or less serious - claim to convey a philosophical content. Based on a corpus of six Italian and French “philosophical fantasies” (Alberti’s Momus, Ariosto’s Orlando Furioso, Folengo’s Baldo, Rabelais’s works, Ronsard’s “seasonal hymns”, and Philippe d’Alcripe’s Nouvelle Fabrique), our study aims at defining this category, and showing how a fictional pattern, initially borrowed by Italian humanists from Lucian of Samosata, has been adapted to new philosophical stakes and controversies. Our last six chapters are devoted to case studies. The five previous ones explore, from a theoretical perspective, the status of incredible fictions in the horatian, platonic and aristotelian poetics: far from being systematically regarded as lies, or considered as artistic failures, they benefit from the high value granted to fictional invention and to the intellectual impact of astonishment. However, their relationship to the allegorical tradition is complex: while they constantly refer to it, they resist to the allegorizers’s investigation. This ambiguity is specific to the products of creative fantasy which, in Renaissance philosophy, is a strongly ambivalent faculty of the soul.