In letter 118, generally dated to the end of 410, Augustine responds in a singu-
lar way to the request of Dioscorus, a young Greek who stopped in Carthage on a study trip,
and who asked him to clarify certain passages in Cicero’s De natura deorum. But the bishop
is alarmed by the desire for praise that moves the recipient. We propose to analyze this letter,
whose philosophical content is undeniable, as a “protreptic” letter. The protreptic intention that
animates the letter allows it to be read as a guide to the proper use of philosophy in the light of
Christian teaching. Following this protreptic dynamic, we will first examine the action of care
and correction that Augustine leads towards Dioscorus, then how he offers him a discourse on
the ends and a table of the history of philosophies inspired by his Dialogues of Cassiciacum and
announcing the City of God. Augustine can then close his remarks with a lesson in hermeneutics
of the Ciceronian text.