The hermeneutic category of «philosophie littéraire» (developed by P. Macherey) is useful for understanding the scope of the works of the philosopher-writers who use the novel and the short story to do philosophy, at the age of the Enlightenment. The notion of «literature» was formed towards the end of the eighteenth century in the works of Lessing, Diderot and Madame de Staël, when the Kantian (contemporary) concept of «philosophy», at the same time, took shape in the system of Criticism. Fromf the perspective of this «philosophie littéraire», the essay deals with the productions of Voltaire and Diderot, noting their character as heuristic investigations (M. Kundera) on the hidden and unspoken aspects of the historical reality with which they are confronted. Voltaire, in Zadig, clarifies the meaning of reason in history and the meaning of a «philosophy of history», sketching out the new notion of «serendipity». Diderot, in Jacques le fataliste (great novel of serendipity), initiates an ironic reflection on freedom and the necessity of human actions, under the sign of Spinoza. Both open new perspectives of philosophical reflection on the register of a philosophie littéraire still to be developed.