 It has already been noted that Porphyry seems to be committed to a version of abstractionism with regard to human beings’ acquisition of knowledge of sensibles. His Commentary on Ptolemy’s Harmonics contains a section about epistemology (11, 5–22, 7), in which the overarching theme is the question of the respective roles of sense-perception and reason (logos) in the acquisition of knowledge. In the course of this discussion he describes a process starting from sense-perception, through apprehension (antilepsis) and supposition (doxastike hypolepsis) to the reception of in the soul of a concept (epinoia), which is identical with the form of the object; hence come knowledge (episteme) and finally understanding (nous). Much of what Porphyry says here is compatible with Middle Platonist and Peripatetic doctrines and with Plotinus (who is rather ambiguous about the details of this process) and indeed with Aristotle. As regards the intellect, however, Porphyry’s account contains an unmistakable reference to Plato’s Seventh letter, which would count against his assent to a purely Aristotelian account of the acquisition of knowledge about sensible objects (see Chase 2010). More research is needed on these aspects of Porphyry’s thought.