The article attempts to analyze the relationship between Renе Descartes and Jean-Louis Guez de Balzac. The study focuses on one of the most amazing episodes of 17th-century French literature, when philosophers, following Descartes, were transitioning to the use of the vernacular, while writers, including de Balzac, were experimenting with new forms of expression, favouring the epistolary genre, among other things. The episode is even more significant because it begins with a young Descartes’ little known reflections on de Balzac’s Letters [Lettres]: published in 1624, the latter provoked one of the century’s most vociferous public disputes. At the same time, the notes provide a good starting point for discussion of a highly controversial topic of the philosopher’s legacy, namely, his ties with 17th-century intellectual libertinism, epitomized by de Balzac, as well as his hostile opponent, the preeminent French poet Thеophile de Viau. The study mainly suggests that, despite certain differences, the philosopher tends to share the two authors’ views of the greatness and freedom of the human self.