The libertine novel is a typically modern invention that found its greatest

diffusion and flowering in the Age of Enlightenment. There are two libertine philosophical novels that best testify to the new alliance forged in the Age of Enlightenment between fiction, fictional narrative and philosophy: Diderot’s Les Bijoux Indiscrets (1747) and Thérèse Philosophe (1748) by the Marquis Boyer d’Argens. In these two texts, there is a happy mixture of fiction and truth, of the production of desire and the Volonté de savoir (Foucault), to know the intimate nature of reality through desire and persuasion, which is the new device that will adopt the novel-form in Modernity, after the Age of Enlightenment. This form of the eighteenth-century libertine novel (erotic, licentious or pornographic), far from representing marginal literature, only of the underground, addressed to a certain public, separated from the «high» and cultivated literature, constitutes rather an archetypal form of the modern novelistic narrative.

In Thérèse, as in the Bijoux, the reader is caught up in a mechanism of fictional reality production that, at first, relies on the full power of the visual imagination, based on sensitive representation; and finally, at a later stage, stimulates the rational sense, the only critical reason, by means of hearing.

At the end of the Eighteenth century, the device put in place in the Bijoux and in Thérèse, with Sade, renders the scenes, and the «essays» put to work by the libertines protagonists of the 120 Journées, unrepresentable: the reader can only listen to them and develops critically reason about them. The eye, a member of sight and imagination, corresponding to Thérèse’s finger, is replaced, with Sade, by the reader’s ear and hearing, as the proper (and deeper) sense of critical Reason.