In his Confessions, Augustine says that he achieved great intellectual insight from what he cryptically calls the “books of the Platonists.” Prior to reading these books, he was a corporealist and was unable to conceive of incorporeal beings. Because of the insurmountable philosophical problems corporealism caused for the Christian belief he was seeking, Augustine claims that this was the greatest intellectual barrier he faced in converting to Christianity. As such, the specific contents and effects of these Platonist books are of (...) great biographical and philosophical interest. Heretofore, the explanation of the contents and effects of these books has not been forthcoming. This essay aims to supply it. I argue that Augustine learned the mereological distinction between pertensive and entensive presence in the books of the Platonists. This distinction is required for properly conceiving of incorporeal beings. In support of this thesis, I show that Augustine himself says that he learned this very distinction, that the distinction is present in Platonist texts that scholars agree were among “the books of the Platonists,” that the distinction is present in one of Augustine’s earliest works, and that this distinction is uniquely capable of resolving the philosophical difficulties he faced as a corporealist. (shrink)