Augustine's City of God (De civitate dei) has been extensively studied, but in-depth commentaries that guide readers through Augustine's often intricate argument are still lacking (see now, however, G. Clark, City of God, Books 1–5 [2021]). With the present book, a revised version of the author's Tübingen doctoral dissertation in theology, DeM. has begun to fill this lacuna by providing a detailed commentary on Book 10. Augustine here continues his argument from the previous two books that happiness, the goal pursued by philosophy and by all human beings, can only be attained through Christ, the true Mediator and ‘universal way of salvation’ (Civ. 10.32). Lesser deities or angels that claim religious worship for themselves are not mediators but evil demons ridden by pride. Pride also prevents Neoplatonists like Porphyry, who, despite their philosophical insight into the nature of the demons, advocate polylatry and promote theurgy, from accepting the grace and incarnation of Christ. One of the Porphyrian treatises Augustine uses, the otherwise unattested De regressu animae (‘On the Ascent of the Soul’), has found considerable attention in scholarship because some have argued that it had influenced him since his first encounter with Neoplatonism (e.g. P. Courcelle, Les lettres grecques en occident [1948], pp. 153–76).

As the title indicates, one of DeM.'s main concerns is to determine what we actually know about Augustine's Porphyrian sources (the De regressu animae in particular) and about how he transformed them. The commentary is therefore selective. For most of the chapters that contain fragments from Porphyry (Civ. 10.1, 8–11, 23–4, 26–7, 30, 32; for a reason not stated, 10.28–9 and 10.31 are omitted) DeM. gives a meticulous line-by-line annotation, in which he analyses the details of Augustine's argument, isolates the authentic Porphyrian material, discusses previous lines of interpretation and advances new suggestions. For the remaining chapters DeM. contents himself with brief structural overviews and general comments, which are helpful but, inevitably, less deep-probing than the comments on the ‘Porphyrian’ chapters. A conclusion summarises the argument of Civ. 10 and lists the most important results from the commentary concerning Porphyry's view on gods and demons, theurgy, the ‘spiritual soul’, reincarnation into animals and the universal way of salvation (pp. 310–15, with cross-references to the relevant discussions in the commentary). Readers primarily interested in Augustine as a source for Porphyry should read these pages first and use them as a guide to the body of the work.

A crucial fact that emerges from DeM.'s painstaking analyses is that we know very little about the De regressu animae. DeM. carefully determines the character and argumentative function of each of Augustine's statements, distinguishing between verbatim quotations (which are very rare), free paraphrases, evaluative comments and inferences and, most interestingly, varying repetitions. Thus, in the course of Civ. 10.32 Augustine moves from a more or less literal quotation of Porphyry's claim that ‘what contains the universal way of salvation’ (quod universalem contineat viam animae liberandae) cannot be found in any single philosophical or religious tradition to freer versions, adapting the original to his own argumentative needs and even, to some extent, Christianising it (p. 279). DeM.'s analyses of the logic and pragmatics of Augustine's arguments greatly profit from his use of contemporary linguistic research (C. Kroon, Discourse Particles [1995]; J. Schrickx, Lateinische Modalpartikeln [2011]); the relevant notes will be useful to anybody interested in Augustine's Latin and the Latin of late-antique argumentative texts in general.

In reconstructing what may have been the original meaning of De regressu animae, DeM. supplements Augustine's reports with evidence from the preserved writings of Porphyry, especially the De abstinentia and the Sententiae. This opens a fresh perspective on much-discussed texts and yields some unexpected results. DeM. questions Augustine's claim that according to Porphyry the purificatory effect of theurgy was limited to the ‘spiritual soul’ (anima spiritalis = ψυχὴ πνευματική) while philosophy was the only means of purifying the higher, rational or intellectual, soul (Civ. 10.9–10). The independent sources rather suggest that for Porphyry there was only one soul, of whose purification and return to the intelligible theurgy and philosophy were two successive steps. It would have been interesting to know DeM.'s opinion on the relationship of this revised picture to the theory of bodily, ‘spiritual’ and intellectual vision from De Genesi ad litteram 12, which because of its parallels to Civ. 10 is generally believed to have a Porphyrian background (C. Tornau, ‘Spiritus’, Augustinus-Lexikon 5 [2021], pp. 557–8). In his commentary on Civ.10.23 DeM. advocates an astrological reading of the oracular claim that ‘only the principles can purify’ (principia posse purgare) as an alternative to the standard interpretation of the verse in terms of the Chaldean Oracles. As DeM. acknowledges, the evidence is slender, but with elusive texts as this one it is legitimate to pursue as many interpretative options as possible. Augustine reads the oracle in the light of what he claims to be Porphyry's theory of principles, which posits a triad composed of the ‘Father’, the ‘intellect of the Father’ (paternus intellectus = πατρικὸς νοῦς, cf. 10.28) and an entity ‘in between’ (horum medium). The background of this much-disputed theory, which, Augustine suggests, betrays a dim insight into the Holy Trinity, is undoubtedly Chaldean. DeM. gives it a fresh reading by suggesting that, even though Augustine contrasts the Porphyrian triad with the Plotinian hierarchy of the hypostases One, Intellect and Soul, the enigmatic intermediate entity may be the soul, which some sources associate with the Chaldean Hecate and which Porphyry's pupil Theodore of Asine seems to have placed ‘between’ the universal and the particular intellect because it proceeded from both (Procl. In Tim. 2.154.4–9 Diehl). In Civ. 10.31 Augustine notoriously claims that Porphyry deviated from Plato and Plotinus by denying the transmigration of human souls into animals. This is contradicted by other sources, especially Nemesius (Nat. hom. 2, pp. 34.18–35.11 Morani = Porph. fr. 447 Smith). DeM. discusses the evidence and sides with Nemesius, arguing that Augustine misunderstood a doxographic source or deliberately chose a version that allowed him to construe a disharmony between Porphyry and the Platonic tradition. His arguments are plausible, but it is regrettable that he does not engage with W. Deuse's subtle reconstruction, which rather prefers Augustine's version and still merits consideration (W. Deuse, Untersuchungen zur mittelplatonischen und neuplatonischen Seelenlehre [1983], pp. 129–67, relegated to a contemptuous footnote on p. 253).

While DeM. is excellent on Augustine as a source of Porphyrian fragments, he is not quite as convincing when it comes to interpreting Augustine's own line of argument. He gives nuanced explanations of the logic, grammar and tone of the single sentences and chapters and the transitions between them, but the coherence of Book 10 as a whole and the rhetorical strategy that holds together its diverse elements remains shadowy. An outline of the book is proposed in the introduction (pp. 14–15) and briefly justified in the conclusion (pp. 310–11), but the commentary itself tends to atomise the text and even makes it appear somewhat repetitive. Repetitions are no doubt there; but, as may be expected from a skilled rhetorician like Augustine, they are meaningful: the theme of the grace of Christ incarnate caps a development on sacrifice to angels and demons in 10.22 and is again prominent in the exhortation to the Platonists to accept Christ's humility towards the end of the book (10.29). Correspondences of this kind mostly go unnoticed in the commentary; the rhetoric of Book 10 largely remains to be studied. This criticism notwithstanding, DeM. has provided an invaluable tool for everyone who wishes to go deeper into the book and into Augustine's engagement with Platonism, and his careful analysis of Porphyry's De regressu animae should be the starting point of any future research on this elusive work.