 Platonists before Plotinus differed in their attitude towards Aristotle (see Karamanolis 2006). Porphyry belongs to those who believed that Plato and Aristotle can be harmonized and in this he is followed by just about all subsequent ancient Platonists. A preserved title of a lost works of his, On the differences between Plato and Aristotle, may seem to give contrary indications (he is also supposed to have written a work about the unity of their thought). Admitting some differences is compatible with a fundamentally reconciliatory attitude (cf. Karamanolis 2006: 243ff.). This positive attitude towards Aristotle is particularly evident from his position on Aristotle’s Categories. The question arises how such an attitude can be reconciled with those passages in Aristotle that seem to disagree with Plato, sometimes expressly. We do not know how Porphyry dealt with others of these, besides Aristotle’s Categories, which appears to modern readers in many respects to be an anti-Platonic work. This is especially notable in its claim that particular sensible substances are prior to the universal species and genera. Porphyry solves this dilemma by insisting that the so-called Aristotelian categories—substance, quality, quantity etc., dealt with in the Categories—are “significant expressions”. That is to say, the Categories is not a work in primary ontology but rather a work about the expressions used to signify the sensible things around us and that the sense in which these are first or primary is that they are the first we meet with in our experience (58, 1ff.). The class of beings signified by a universal term of this sort is indeed prior to the universal term, e.g., the class of pale things to the universal term ‘pale’. As Strange (1987, 1992) notes, this, however, does not affect the basic ontology. So interpreted the Categories is innocuous from a Platonic point of view: the realm of Platonic intelligible Forms, which are universals of a different kind than the expressions involved in the Categories, can be kept intact. The universals the Isagoge and Porphyry’s commentaries on the Categories are concerned with are post rem universals abstracted by the mind from external objects met with through sense-perception.