Book V follows the young Augustine from Carthage (where he finds his students too rowdy for his liking) to Rome (where he finds them too corrupt) and on to Milan, where he will remain until his conversion. Manichee beliefs begin to lose their luster for him during this period, and by the end of the Book he considers himself an unbaptized Christian (a "catechumen": a beginner who is being taught the principles of Christianity; a neophyte). Augustine encounters a number of important figures during this period of relentless searching, including Ambrose (the Bishop of Milan, who will eventually baptize Augustine) and Faustus, a Manichee luminary. He also encounters the profound doubt of the skeptical school and comes close to total skepticism in his own philosophy.

[V.1-13] Augustine begins by reminding us that everything and everyone is part of the whole of God's creation. This is in line with the Neoplatonic ideas discussed in Book III; nothing is inherently evil, and even the most "wicked" people continually praise God (though they do not know it). "You [God] see them and pierce their shadowy existence," he writes, and "even with them everything is beautiful, though they are vile." (Later, in his City of God, Augustine will liken such apparently evil people and things to the dark areas in a beautiful painting).

At age twenty-nine, still in Carthage, Augustine gets to meet Faustus, a respected sage of the Manichees. Before describing the encounter, Augustine takes the opportunity to make some points about the difference between scientific astronomy and the Manichee account of the heavens, a comparison that he was considering at the time.

Though he now knows that science is worthless without praise to God (who made the scientists and even the numbers they use), at the time he was impressed by astronomy's reliability in accounting for heavenly movements. In contrast, the Manichee account (which included claims that the eclipses serve to "hide" heavenly battles) was starting to seem inaccurate.

Augustine is initially impressed by the modesty Faustus exhibits--the sage simply refuses to theorize about subjects he doesn't know intimately (astrology is an example). Interestingly, however, Faustus' rhetorical flashiness doesn't impress Augustine, who claims that by this time he had learned to value the content of speech over mere loquacity. The net result of the interview was disillusionment: Augustine departed with more doubts than ever about Manichee myths and pseudo-science.

[V.14-21] Finding his students too rowdy and altogether too reminiscent of himself when he was a student, Augustine departed Carthage for Rome. Monica, who had accompanied him to Carthage, grieved at his departure, and Augustine confesses that he told her a white lie in order to get on the boat to Rome without delay.

Almost immediately on arrival in Rome, Augustine was stricken gravely ill (in referring to this illness as a punishment from God, he makes the first-ever use of the phrase "original sin"). For his recovery, he gives credit to God, of course, but also to Monica's prayers.

Appraising what he knew when he began living in Rome, Augustine makes a reference to "the Academics," the skeptical school that arose at Plato's Academy. He thought the Academics "shrewder than others," and their pervasive logical challenges to any belief at all had, in Augustine's mind, a particularly devastating effect on the somewhat goofy postulates of Manichee mythology.

Still, however, the Manichees had left Augustine plagued by images when he thought of God or of evil: God as "a physical mass" or "a luminous body," even evil as "a malignant mind creeping through the earth." Even worse, his lingering dualism (the idea that God and evil are two warring substances) meant that he still took no real responsibility for his sins. Worse still, he accepted the Manichee disbelief in Christ's incarnation in human form, picturing him instead as a wholly divine being "emerging from the mass of [God's] dazzling body."

[V.22-25] Things were going poorly in Rome, where Augustine quickly discovered his students to be cheaters who would often walk out just before the end of classes to avoid paying the teacher. Disgusted, Augustine took an opening for a teacher of rhetoric in Milan. This will turn out to be an important move: it was "to end my association with [the Manichees], but neither of us knew that [yet]." In Milan waited Bishop Ambrose, who would be a major influence in Augustine's conversion to Catholicism.

In Milan, Augustine became increasingly open to Christian philosophy and theology, primarily for the reason that he hears the Old Testament "figuratively interpreted" for the first time. This experience is the practical catalyst that allows Augustine to begin to move toward total faith in the church. Genesis, with its apparently intractable issues of a God that "created" and did things like a being who lived in time and in a body, suddenly seemed much more reasonable when "expounded spiritually." The apparently sinful actions of the prophets of the Old Testament also took on new sense when read metaphorically.

Augustine became at this point a near-convert, a "catechumen" waiting for a final sign from God that he should take the plunge and be baptized. The one remaining obstacle to his total belief, he says, was his persistent imagery of God as a physical mass or ghostly substance, expanded or diffused through everything like a gas. He still lacked the concept of a spiritual substance.