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."