This is a ground-breaking study of the consequences of a central problem in Aristotle's Metaphysics in the interpretation given to it by Islamic and Christian Aristotelian philosophers: the relationship between individuals as individuals, and individuals as instances of a universal. Father Booth begins from an examination of the factors causing the aporia in the centre of Aristotle's ontology, going on to elaborate the way in which it occurred sometimes with confused reactions among the Greek, Syrian and Arab commentators, and to note in particular the modifications to the weighting of elements in Aristotle's ontological figures (differing in detail, but in tendency the same) when his ontology was brought into the union with Platonist and other thought conventionally known as Neoplatonism'. The discussion culminates in two chapters on the different reconciliations of the radical Aristotelian and the Neoplatonist traditions, proposed by Albertus Magnus and Thomas Aquinas, in which the factors in the aporia have a key importance.