This contribution to Richard Sorabji's series of Ancient Commentators on Aristotle is shorter than many, covering only the dissertation on the nature of time which makes up the latter half of the fourth book of the Physics. The annotation is also not so copious as in some other volumes, though B. performs an important service to the reader with her long diagnosis of the ambiguity of a passage (p. 63, 755.36 Vitelli) in which Philoponus adumbrates a contrast between the period of a thing's existence and the time or times during which it does not exist. As she observes here (p. 110), the question was of interest to Philoponus because he differed from Aristotle in holding that there was one present instant, a ‘now’, which was the first, and that another will mark the end of the temporal series. Nevertheless (see p. 111, elucidating the discussion of Physics 222a10ff.), he does not defend his view in this commentary, but alludes to a previous work on Physics 8 which now survives only in an Arabic paraphrase. Nowhere in the second half of Book 4 do we find that sharp reprehension of Aristotle which occasionally breaks the equable tone of the commentaries on other books – the third, for example, where Philoponus intervenes to prove that, on Aristotle's own principles, the world cannot have an infinite history.

Sorabji suggests in his introduction that the present work was directed to ‘a more elementary group of students than those who were regaled with the lectures on Physics Book 4, Chapter 8, introducing the theory of impetus’ (p. ix). At the same time, taking up another long note by B. (n. 194 at p. 113), he points out that in his comment on Physics 4.13.222b33ff. (771.20–8 Vitelli), Philoponus has tacitly improved on an obiter dictum of the Stagirite with his argument that speed round a bend may be demonstrably faster than speed in a straight line even when the object travelling round the bend takes longer to complete its journey (p. x). Sorabji concedes that the ‘brilliant’ Philoponus has not anticipated Newton's notion of inertia in his innovatory theory that projectiles are carried by their own impetus rather than by the propulsive force of air. Such animadversions, typical of his approach to Philoponus since he began to commend his works to the public, imply that this philosopher is most interesting to us when perceived as a man ahead of his time. There is also, however, a case for treating him as a man who was answerable to his predecessors and contemporaries: one misses in Sorabji any acknowledgement of Philoponus' Christianity, while one might have hoped that B., in annotating his reflections on the relation of time to motion (pp. 85ff, Vitelli 776.5ff., on Physics 223a229ff.), might have offered some comparison with the famous precursors of this discussion in Plotinus, Enneads 3.7 and Augustine, Confessions 10. This is not to deny that B. and Sorabji have produced another fine contribution to a series which has been characterised at all times by deft scholarship and reliable translation.