Returning to Thagaste from his studies at Carthage, Augustine began to teach rhetoric, making friends and chasing a career along the way. Though giving some account of these worldly matters, Augustine spends much of Book IV examining his conflicted state of mind during this period. Having begun his turn toward God (through the desire for truth) but continuing to be ensnared in sinful ways, Augustine wrestled painfully with the transitory nature of the material world and with the question of God's nature in relation to such a world.

[IV.1-7] Augustine opens this Book with a short description of his pursuits in Thagaste, which he says consisted primarily of "being seduced and seducing, being deceived and deceiving." He points out that he spent his public hours in pursuit of empty, worldly goals (his ambition to attain public office, which required great skill in oratory as well as contacts and money) and his private hours pursuing a "false religion" (Manicheism). This hypocritical life, in which he sought both material gain and (false) spiritual purity, was nothing but a form of "self-destruction."

Chief among Augustine's regrets about this period are his career as a "salesman" of the "tricks of rhetoric" (he was an instructor in rhetoric, partly to students at the law courts) and his persistence in keeping a concubine. Although he doesn't say much about this unnamed woman, she stayed with Augustine for nearly ten years, eventually bearing him a son (Adeodatus, who would die at age seventeen).

Augustine does recall, however, making some progress toward truth. In part through the influence of his close friend Nebridius, Augustine concluded that astrology is "utterly bogus." (This will prove an important first step in discarding the colorful Manichee mythology, which contains a number of bizarre accounts of the heavenly bodies). Shunning this dubious form of prediction and the elaborate sacrificial rituals that often accompanied it, Augustine began to attribute its occasional success almost entirely to chance, which he sees as "a power everywhere diffused in the nature of things."

[IV.8-18] Such considerations were interrupted for a while when a close friend of Augustine suddenly passed away, leaving him grief-stricken: "everything on which I set my gaze was death." Realizing now that his grief would have been alleviated by faith in God, Augustine concludes that his grief meant he had "become to myself a vast problem." Attached to the transient, embodied things of the world (rather than to God), he suffered grief when they disappeared.

This theme gets a lengthy treatment here, as Augustine investigates the unreliability and transience of things and the permanence of God. Misery, he writes, is due to an unreasonable attachment to "mortal things." Further, this is always the state of the soul without God--misery is everywhere when there is nothing eternal to depend on. "Where," Augustine asks, "should I go to escape from myself?... Wherever the human soul turns itself, other than you, it is fixed in sorrows."

With everything around him looking like death, Augustine again left Thagaste for Carthage. His state of mind at this point was not good, but the lessons he learned from his grief are still with him. The chief lesson, again, is transience. Every material thing, no matter how beautiful, is demarcated by a beginning and an end--no sooner does anything come to be than it is "rush[ing] toward non-being." These things, then, should only be the object of love in as much as one is loving the presence of God in them.

God, on the other hand, is "a place of undisturbed quietness." Though the things of the world pass away, taken together they are part of a timeless whole. Through God, one can perceive this whole, since God is the ground for all existence. If this is recognized, temporality shouldn't be a concern.

There are a few references here to speech and language in the context of transience. Speech for Augustine is problematic in two deeply intertwined ways. Firstly, it is always successive--one cannot say anything all at once. Thus, speech (and writing, for that matter) is always bound in temporality, that state which is unknown to God but suffered by his estranged creation. In addition, speech is incapable of accurately describing God (a concern of the first pages of the Confessions). In both form and content, then, language is a poor tool with which to pursue the truth of God. There is an exception, however: prayer or confessions, forms of direct address to God's mercy. (The Latin for this word carries the double meaning of admitting guilt to God and praising God.) God is always listening, and direct address to him is the format for the Confessions as a whole.

[IV.19-27] Augustine devotes some time to a reappraisal of a book he wrote during this period in Carthage, called The Beautiful and the Fitting. The book argued that there were two kinds of beauty: beauty inherent in the thing itself and beauty by virtue of the thing's use value.

There are a number of retractions Augustine wants to make concerning this work, most of which he now considers "miserable folly." First to go is the dedication, which was made to Hierius, a Roman orator well known at the time. Augustine recognizes that he dedicated his work to this man solely because Hierius was popular: "I used to love people on the basis of human judgement, not your judgement, my God."

In The Beautiful and the Fitting, Augustine also argued that there is an evil substance that causes division and conflict, whereas the nature of the good is the unity and peace whose most perfect instantiation is in pure mind. Two things are wrong with this view, and both are Manichee errors. First, there is the idea of evil as a substance--an impossibility if God is to be omnipotent and omnipresent. Second, there is the idea of the mind as "the supreme and unchangeable good."

Augustine considers his second error in particular to be "amazing madness." The soul, he now knows, is not itself the fundamental truth or good. It participates in God, but is not itself God or some small piece of God. The error about evil and this error about the soul together constitute, in Augustine's eyes, a massive arrogance characteristic of Manichee beliefs: evil is thought to exist due to God's impotence (rather than human impotence), and humans mistake themselves for God.

With this retraction made, Augustine moves from what he was writing at the time to what he was reading: Aristotle's Categories. Like the Neoplatonists, Augustine now understands Aristotle's work as a system applicable only to this world (and to logical exercises in general), but not to God. At the time, however, he was puzzled and misled. Trying to conceive how God could have beauty and magnitude as attributes (following Aristotle's system), he failed to realize that "you [God] yourself are your own magnitude and your own beauty."

This error led Augustine further into the false problems of trying to imagine God. With the influence of Manichee beliefs all around him, he pictured God as "like a luminous body of immense size and myself a bit of that body. What extraordinary perversity!"