This Balzac was also an important French writer, not of the nineteenth century, but of the seventeenth. He was, like Descartes, initially educated by the Jesuits and later was at the university in Leiden. His literary reputation was based largely on his correspondence, which was twice collected and published during his lifetime. He was elected, in some capacity, to the French Academy (he was several times favored by appointments from Richelieu). His place in history was secured not by what he said (even his supporters loudly failed to describe him as a genius) but by how he said it (everyone acknowledged that he had contributed to the development of the modern French language).

He felt “the closest and most sincere friendship” after Descartes’ espousal of his cause in 1625 with the Papal Legate in France in dealing with the aspersions against him by the publication of correspondence by a priest named Goulu. The issue was Balzac's perceived self-centeredness (his enemies called him “Narcissus”). According to the later author of the cogito, “it is sometimes necessary to speak of oneself with the same freedom that one does of others.” Not incidentally, Descartes’ judgment of Balzac, even if written in Latin, might be proleptically the most Proustian text in all of French literature (AT I 7–11). In any case, the text is important for understanding Descartes’ early thoughts on attention in clearly and distinctly perceiving the truth (see clarity and distinctness).

He “esteemed the heart of his friend more than his mind,” but Descartes nonetheless praised the purity of Balzac's literary style, which he compared to the health of the body, “never more perfect than when it is least noticed.” When the Discourse on Method appeared, Descartes wrote to Balzac in the hope that his own lack of style in the work he was sending him might be overcome by Balzac's affection for him and result in a favorable judgment of it.

Balzac expressed a strong desire to visit Descartes in Holland, indeed to take up residence with him there, but his proposal came to naught, perhaps because of Villebressieu, who had a different conception of how, and with whom, Descartes should spend his time.