Z. is a fine theologian and intellectual historian whose first book on Theology as Science in the Nineteenth Century (2013) is an impressive study of how biblical philology and its subsequent, provocative critical historiography developed as a methodological and a theological commitment in the nineteenth century, especially in German-speaking academic environments. He brings his technical skills as a philosopher and intellectual historian to bear on an apparently quite different topic, that goes to the heart of the transition from the recognised tradition of ancient Greek philosophy through Neoplatonism to the Christian writings of late antiquity. It is, however, a topic that is also central to nineteenth-century anxieties, not least in historiography, namely, the theory of time.

Z. is fascinated by an aporia that first appears in Aristotle, at least in its iconic form, in his Physics: ‘Someone might raise the puzzle whether, if there were no soul, there would be time or not’ (p. 3). This question is posed in the middle of the few sentences that Aristotle dedicated to temporality as a notion, sentences that R. Sorabji calls the most influential and important writing on time for many centuries to come, and which U. Coope has analysed in an excellent and lengthy book (Time for Aristotle [2005]). Z. is interested in just this puzzle, and in how it was reworked in antiquity, to become eventually a key moment of tension in later Christian theology. Is time to be understood as cosmic, or is time to be understood as personal experience? Can time be objective or does it always rely on the subjectivity of human measurement? To explore this large-scale question, he offers five brief chapters – the book has only 85 pages of exposition –, which, in turn, introduce the issue; discuss Aristotle's formation of the paradox; look at Neoplatonist interpretations of this crux in Aristotle; continue into patristic thought; and provide a brief conclusion. The book is poised between being too long for an article and too short for a standard book: this form gives it both its strengths and its weaknesses. It is written with great clarity, careful recognition of the difficulties and an engaging sense of an intellectual history that became a matter of burning importance to the participants in the debate. The details of this debate were likely to be of little concern, one suspects, to the congregants of the churches taking shape across the Roman Empire. But the implications of such arguments about time – the nature of history, humankind's place in it and the consequences of the end of days for morality and daily life – became the backbone of Christian normativity. What was at stake was the human soul.

There are two significant strengths in the book's precise focus. The first and most important is the line of intellectual history that it reveals. Z. states that in antiquity Aristotle was taken to argue that time could not exist without the soul. He duly notes that Aristotle's engagement with Plato is far more complex, and makes an attempt to locate time neither as identical with the phenomena of nature nor as wholly separate from them. Boethus of Sidon in the first century bce insisted that cosmic time existed separately from the human soul. Two centuries later, Alexander of Aphrodisias, from a Peripatetic background, argued that one needs to distinguish between the possibility that something countable could exist without a person counting, on the one hand, and, on the other, that something countable could exist as countable. Alexander ‘insists in an almost hermeneutical manner on the irreducibility of the awareness of time for its existence as time without falling into an idealist identification of the cosmos with our idea of it’ (p. 83). But Boethus also added a ‘world soul’ without which movement and time would be impossible. Plotinus’ Ennead 3.7 is a crucial juncture in this ongoing history. Plotinus sought to reintroduce the Platonic notion that ‘time can only be properly conceived from the perspective of eternity’ (p. 84). Simplicius takes this notion to the extreme that personal or individual awareness of time plays little or no role in his theorising. In contrast to this tradition, Christian writers – and Z. focuses briefly on Gregory of Nyssa before turning inevitably to Augustine – demand that time is created by God and has a cosmic reality, but also rejected the notion of the world soul. Consequently, Christian writers adopted an intensely personal notion of the experience of time that earlier philosophers had downplayed: Augustine's Confessions with its intricate analysis of memory and hope alongside a theory of cosmic time is paradigmatic. In this history Z. is rehearsing a case first made in outline by John Callahan from the 1940s onwards – as he acknowledges. It shows up exactly how one crucial element of Neoplatonism was significantly not adopted by Christian thinkers.

The second advantage of the book's delimitation of argumentation is the clarity it brings to the immensely complex world of how time and the soul might be interrelated, and, if briefly, to the long-term implications of Aristotle's conundrum. It tells a neat story, sharply (no bad thing in an academic book). Yet this is also the book's most obvious demerit – the price at which such clarity is bought. Change and movement are central to Aristotle, but this argument emerges for Z. without reference to Parmenides, whose provocations, along with Zeno's paradoxes, find no place in the tradition. Aristotle is also much vexed by the problem of what is ‘now’ – can it have a duration? Can it be measured? – a question that Augustine too finds deeply worrying. Can you be present in time? Similarly, Augustine's concern with measuring time is framed by a wider set of salient questions. Augustine begins with Genesis, the problem of creation, and expands this to consider his own creation – did his soul exist before his birth and, if so, where, and was it always so? He is also struggling in a profound way with how to understand that God stands outside time. How can God have said ‘let there be light’ when to say ‘let there be light’ takes time and God is outside time? Because Augustine is mired in human language and thought – which must be quite unlike God's language and thought –, he knows it makes no sense to ask what was there before creation, before time – but can have no way of not formulating the question in this inevitably senseless way, even as he does not want to ask it, because he cannot get outside the time of syntax and grammar. The apophatic theology of the Fathers, a necessary tempering of the desired philosophical clarity, does not feature enough in Z.'s exposition. Nor, from a different perspective, does astrology. Yet if there is one area where cosmic time and personal experience come up against each other, it is in astrology, a science Augustine was deeply committed to in his younger days and deeply opposed to in his later years.

Astrology was also a topic that vexed Gregory of Nyssa – and Gregory of Nazianzus. The cast list of this book is restricted indeed. Not only does The Theologian (as Gregory of Nazianzus was known in Byzantium) get no airtime, although he writes compellingly about time, all the other authors who are not registered in the canon of philosophers, but who were part of the intellectual scene in these centuries, are silenced. It was Nonnus, after all, in the fifth century, who started a Paraphrase of the Gospel of John with the shocking but theologically charged word achronos, ‘timeless’. For Z., it seems, the politics of Nicaea – aggressively a realpolitik as well as theological argument about time – are subordinate to the tight line of argument he follows. The argument is well made: but it comes at a real price if we want to understand why time mattered so much to Christian writers.