This brilliant book should be welcomed as a major contribution to Aristotle scholarship. Halper offers a lucid interpretation of Books VI-IX of the Metaphysics. His interpretive key is the thesis that for Aristotle the measure of being is unity; hence the search for being in the primary sense is an inquiry into what is itself most one and, in turn, the cause of unity in other things. Halper brings this thesis to bear on every chapter of the central books, and the results are deep and exciting.

       Many difficult passages yield fresh sense. To cite some particularly striking cases, Halper offers illuminating readings of Aristotle's treatments of the causes of accidents (VI.2-3); the identity of essence and 'thing' (VII.6, prepared by 4-5); the doctrine of proper differentiation (VII.12); the related notions of the continuity (VII.17) and the differentiae of matter (VIII.2); the unity of the composite (VIII.6); and being as truth (IX.10, prepared by VI.4).

       Halper's close study of particular passages makes all the more compelling the architectonic unity he is able to reveal in VI-IX as a whole: after distinguishing the four ways "being" is said (VI.2) and then setting aside being as accident (VI.2-3), Aristotle goes on to trace pros hen series in each of the three per se ways, being as truth (V.I4, IX.10), categorial being (VII-VIII), and being as potentiality and actuality (IX.1-9); these series converge on form, disclosing it as incomposite, essence, and actuality, respectively.

       Halper offers extended exegesis and argument for the heterodox claim, central to his interpretation, that Aristotle takes form to be one both in formula and in number. This, he shows, is necessary if form is to be cause of the continuity of matter in the composite (VII.17) and, thereby, of its own unity with matter as the composite (VIII.6). It is these requirements, in turn, that lead Aristotle to the complementary conceptions of proper matter as the capacity of parts to move together and of form as first actuality.

       This interpretation of the unity of form positions Halper to offer an original way through what modern scholarship has come to fix on as a central contradiction in VII. How can substance be form if, on the one hand, no universal can be substance (VII.13-16) and, on the other hand, many composite individuals share the same "indivisible" form (VII.8)? To point toward the crux of Halper's carefully reasoned solution: Aristotle's arguments against the universal's being substance turn on its lack of oneness in number; that form has this oneness, and in a higher measure than the composite individual, at once frees it from this objection and qualifies it to be the substance of the many composites.

       One and Many in Aristotle's Metaphysics is deep, comprehensive, helpful at every level.  I know of no better companion for anyone undertaking serious study of Metaphysics VI-IX.