In the catalogue of his works Salutati lists De fato et fortuna (Entry n. 39) after De seculo et religione. The first part was written in July 1396 and the second was unquestionably finished by 28 September 1399. While probably his most complex work, it cannot be counted among his most successful.

The first part, De ordine causarum, states the need for a prime mover and the second, De fato, distinguishes among the various meanings of fate to determine its relationship with providence. What is striking about these sections is their overwhelming emphasis on the Augustinian view of grace and the rigorous affirmation that man cannot comprehend God’s workings intellectually but solely through experience.

The third part, De fortuna, opens with a lively attack on astrologers and then geomancers. According to Salutati, one can accept the idea of fate as dispositio divina, but the same cannot be said for astrological predetermination.

The most distinctive aspect of this work with respect to similar works from around the same period is the treatise form, as if to prove that the work is philosophical/political rather than literary in nature. Indeed, the energy that Salutati invested in collecting sources and documents to draw up an annotated history of the positions of ancients and moderns alike towards fate and fortune is confirmed by the use of the codices from his library, which are often cited word for word; in some cases, the gloss “nota de fato” is penned in their margins.