 Like most ancient philosophers, Augustine thinks that the human being is a compound of body and soul and that, within this compound, the soul—conceived as both the life-giving element and the center of consciousness, perception and thought—is, or ought to be, the ruling part. The rational soul should control the sensual desires and passions; it can become wise if it turns to God, who is at the same time the Supreme Being and the Supreme Good.  In his Manichean phase, he conceived of both God and the soul as material entities, the soul being in fact a portion of God that had fallen into the corporeal world where it remained a foreigner, even to its own body (De duabus animabus 1; Confessiones 8.22). After his Platonist readings in Milan had provided him with the adequate philosophical means to think about immaterial, non-spatial reality (Confessiones 7.1–2; 7.16), he replaced this view, which he later represents as a rather crude dualism, with an ontological hierarchy in which the soul, which is mutable in time but immutable in space, occupies a middle position between God, who is totally unchangeable immaterial being (cf. MacDonald 2014), and bodies, which are subject to temporal and spatial change (Letter 18.2). The soul is of divine origin and even god-like (De quantitate animae 2–3); it is not divine itself but created by God (the talk about divinity of the soul in the Cassiciacum dialogues seems to be a traditional Ciceronian element, cf. Cary 2000: 77–89; for a Plotinian interpretation see O’Connell 1968: 112–131). In De quantitate animae, Augustine broadly argues that the “greatness” of the soul does not refer to spatial extension but to its vivifying, perceptive, rational and contemplative powers that enable it to move close to God and are compatible with and even presuppose immateriality (esp. ib. 70–76; Brittain 2003). An early definition of soul as “a rational substance fitted for rule over a body” (ib. 22) echoes Platonic views (cf. the definition of the human being as “a rational soul with a body” in In Iohannis evangelium tractatus 19.15; O’Daly 1987: 54–60). Later on, when the resurrection of the body becomes more important to him, Augustine emphasizes—against Porphyry’s alleged claim that in order to be happy, the soul must free itself from anything corporeal—that it is natural and even desirable for a soul to govern a body (De Genesi ad litteram 12.35.68), but he nevertheless remains convinced that soul is an incorporeal and immortal substance that can, in principle, exist independently of a body. In the Soliloquia (2.24), following the tradition of Plato and of Cicero’s Tusculan Disputations, he proposes a proof for the immortality of the soul which he expressly introduces as an alternative to the final proof of the Phaedo (Soliloquia 2.23, cf. Phaedo 102d-103c). The proof is constructed from elements from Porphyry’s Isagoge and his Commentary on Aristotle’s Categories (rather elementary texts that Augustine would have encountered long before his Platonic readings at Milan) and seems to be original with him (Tornau 2017). It says that since truth is both eternal and in the soul as its subject, it follows that soul, the subject of truth, is eternal too. This is fallacious, because if truth is eternal independently of the soul it cannot be in the soul as in its subject (i.e., as a property), and if it is a property of the soul, it cannot ensure its eternity. In the incomplete draft of a third book of the Soliloquia preserved under the title De immortalitate animae, Augustine therefore modifies the proof and argues that soul is immortal because of the inalienable causal presence of God (= Truth) in it. It turns out however that even if this version of the proof is successful, it only demonstrates the soul’s eternal existence as a (rational) soul but not its eternal wisdom (De immortalitate animae 19; Zum Brunn 1969: 17–41 [1988: 9–34]), in the hope of which the interlocutors had set out to prove the immortality of the soul in the first place (Soliloquia 2.1). After De immortalitate animae, Augustine never returned to his proof. But neither did he disown it; as late as De trinitate (13.12), he endorses the Platonic axiom that soul is by nature immortal and that its immortality can, in principle, be proven by philosophical means. He also sticks to his conviction that immortality is a necessary condition of happiness but insists that it is not a sufficient condition, given that immortality and misery are compatible (cf. De civitate dei 9.15 on the misery of the wicked demons). True happiness will only be realized in the afterlife as a gift of God’s grace, when, thanks to the resurrection of the body, not just the soul but the human being as a whole will live forever. Resurrection, however, is not susceptible of rational proof; it is a promise of God that must be believed on Scriptural authority (De trinitate ib.).