Scholars have accepted Augustine’s Ad Simplicianum as his definitive transition to his later theology due to its obvious shift between books one and two; and, Augustine’s statements that he began to understand grace during this time and that his theology had already countered the Pelagian heresy prior to its appearance. Numerous novel doctrines such as initial faith being God’s gift because of humanity’s “dead will” and God’s unilateral determination of individuals’ eternal destinies erupt in Ad Simplicianum without prior formative concepts. Scholars have noted his continued emphasis on unmerited grace, but that his works, letters, and sermons for another fifteen years are relatively silent on these novel doctrines. A chronological examination of Augustine’s works, letters, and sermons reveals that only in AD 412 did the Bishop of Hippo begin to gradually develop his later theology. Between 397 and 412, Augustine persists in teaching his prior theology. In contrast, one single letter (Ad Simpicianum 1.2 ) erupts with a plethora of novel doctrines of relative maturity. This suggests that like numerous other works revised years or decades later, Augustine himself revised Ad Simplicianum after AD 411. This paper will provide an alternative theory to reconcile his comments in Retractationes, Predestinatione sanctorum, and De dono perseverantiae. Augustine’s rhetorical skills shine as he cautiously maneuvers to avoid the sin of lying while defending the faith against Pelagian heresies. By demonstrating Augustine’s revision of Ad Simplicianum, the otherwise inexplicable fifteen-year lacuna transforms into a cohesive understanding of his theological development.