One might think that the whole Enlightenment enterprise, continuing the movement begun by Descartes, was aimed at producing clear, distinct knowledge, and rejecting shadows, blurring and, in general, anything that falls on the side of the indefinite, the vague, and hence anything that might appear unclear. On the contrary, we'd like to show here that the Enlightenment, far from being simply a continuation of the Cartesian elucidation movement and a radicalization of the classical demand for clarity, was fascinated by all generators of blurring, by everything that resists the enterprise of distinction, analysis and decomposition into simple truths. The Enlightenment had a passionate interest in disorder, movement and the undefined, and it's this paradoxical interest in vagueness, in all its forms, that we'd like to focus on here, following its marks in the subject (sensation, language), in the object (nature as chaos and continuity) and in literary representation (the novel as the art of vagueness between literature and philosophy).