The present study, after a quick codicological investigation of the two surviving manuscripts of the De trinitate by pseudo-Didymus, in which it is concluded that one is a copy of the other, focuses on the lexical analysis of the first book of the mutilated trinitarian treatise. By showing divergences from the authentic works of Didymus, alongside parallels with the writings of the Cappadocian Fathers, Cyril of Alexandria, Theodoret, of other late patristic authors, as well as with those of the Neoplatonic philosophers, in particular Proclus, the author concludes that the chronological position of De trinitate should not be before the end of the 5th century, and suggests a possible origin from an environment of Antiochene influence.

In De immortalitate animae Augustine is not satisfied with completing his proof of the immortality of the soul – which had been left open in the second book of the Soliloquies –; he also answers some possible objections, demonstrating that the rational soul cannot cease to exist, it cannot die, nor can it change into an irrational body or soul. Furthermore, remaining faithful to the programmatic declaration of never wanting to stray from the authority of Christ (Acad. 3, 20, 43), he specifies the ontological status of the soul by affirming that it is, in itself, mutable and therefore not of a divine nature, as Varro had argued. Nor is it a substance foreign to the body, as the Platonists claimed, because the soul has an appetitus ad corpus and, if it questions itself, it easily discovers that it desires nothing else «except to do something, to know with intelligence or with the senses, or only to live, as far as this is in its power» (nisi agendi aliquid, aut sciendi, aut sentiendi, aut tantummodo vivendi in quantum sua illi potestas est).