 There are two intertwined issues debated by scholars relating to Porphyry’s philosophy of logic: One has to do with Porphyry’s understanding of the relationship between Aristotelian categories as “signifying expressions” and the things these expressions refer to, the ontology. His remarks in the Isagoge indicating that he will eschew difficult ontological issues (1, 9–16) as well as the absence of distinctively Platonic views in the Isagoge and the extant commentary on the Categories have lead scholars to suppose that he regarded logic as an ontologically uncommitted discipline that could be freely adopted by different schools of different persuasions (Ebbesen 1990; Barnes 2003). There are strong reasons to believe, however, that Porphyry the logician cannot so easily be separated from Porphyry the philosopher. The Isagoge and the extant commentary on the Categories are intended as elementary works but not thereby philosophically neutral, unconnected with Porphyry’ substantial views on the nature of things. That Porphyry’s interpretation of the Categories brings with it certain ontological commitments is evident from the fact that he took the signifying expressions, the categories, to reflect the structure of the sensible world (cf. In Categorias., 58, 21–29; Chiaradonna 2008). This is by no means a trivial assumption. The other issue has to do with Porphyry’s stance towards Plotinus’ account of the Aristotelian categories in Ennead VI.1 and 3. Plotinus understands the Categories as a work in ontology rather than being about expressions and he takes a critical view of it as such. What is debated is to what extent this shows a deep disagreement between the two thinkers not only about the interpretation of Aristotle’s Categories but about the structure of the sensible realm and its relation to the intelligible causes. Chiaradonna (2002: 48–54) argues forcefully, and in this author’s view successfully, that there is a breach with Plotinus on the issue. Porphyry accepted and adopted Aristotelian essentialism about sensible objects along with Aristotle’s categorization of them and sought to harmonize this view with his Platonist position about the intelligible causes of this realm. Plotinus did not share this view. Porphyry’s line won the day in late antiquity. The opposite view, that there is a smooth continuation between Plotinus and Porphyry on the Aristotelian categories, is argued by Frans de Haas (2001).