With the growth of interest in later Greek philosophy, the importance of Plotinus (AD 205-270) as a seminal influence on later thinkers, both pagan and Christian, is being increasingly recognized. The Enneads have been readily available for some time, both in Greek and in English translation, and there is no shortage of scholarly writing on the Enneads in general, and on particular aspects of Plotinus' thought. However, apart from Michael Atkinson's translation and commentary on Ennead V.1 (Clarendon Press, 1985), there has been no major commentary in English on any single treatise. Plotinus' Greek is notoriously obscure, and mere translation often sheds little light. Barrie Fleet's translation and commentary on Ennead III.6 elucidates the text of a major treatise in which Plotinus uses the concept of impassivity to shed light on three questions of importance to Platonists: the nature of change in the human soul; its analogue in the Sensible World; and the nature of Matter. Dr Fleet shows how texts of Plato and Aristotle, and Hellenistic commentaries on them, were central to the seminars held in Rome under the leadership of Plotinus. This treatise is the outcome of one such seminar. All Greek quotations in the commentary are translated into English, and all Greek terms are either translated or transliterated, making this edition fully accessible to readers with or without Greek.

In "Categories" chapters 7 and 8 Aristotle considers his third and fourth categories - those of Relative and Quality. Critics of Aristotle had suggested for each of the non-substance categories that they could really be reduced to relatives, so it is important how the category of Relative is defined. Arisotle offers two definitons, and the second, stricter, one is often cited by his defenders in order to rule out objections. The second definition of relative involves the idea of something changing its relationship through a change undergone by its correlate, not by itself. There were disagreements as to whether this was genuine change, and Plotinus discussed whether relatives exist only in the mind, without being real. The terms used by Aristotle for such relationships was 'being disposed relatively to something', a term later borrowed by the Stoics for their fourth category, and perhaps originating in Plato's Academy. In his discussion of Quality, Aristotle reports a debate on whether justice admits of degrees, or whether only the possession of justice does so. Simplicius reports the further development of this controversy in terms of whether justice admits a range or latitude (platos). This debate helped to inspire the medieval idea of latitude of forms, which goes back much further than is commonly recognised - at least to Plato and Aristotle.

Chapters 5 and 6 of Aristotle's "Categories" describe his first two categories, Substance and Quantity. It is usually taken that Plotinus attacked Aristotle's "Categories", but that Porphyry and Iamblichus restored it to the curriculum once and for all. Nonetheless, the introduction to this text stresses how much of the defence of Aristotle Porphyry was able to draw out of Plotinus' critical discussion. Simplicius' commentary is our most comprehensive account of the debate on the validity of Aristotle's "Categories". One subject discussed by Simplicius in these chapters is where the differentia of a species (eg the rationality of humans) fits into the scheme of categories. Another is why Aristotle elevates the category of Quantity to second place, above the category of Quality. Further, de Haas shows how Simplicius distinguishes different kinds of universal order to solve some of the problems.

Book two of Aristotle's "Physics" is thought by some to be the most interesting and representative book in the whole of his corpus. It explains his conception of nature, of physics as opposed to mathematics, of causation and explanation, of chance and of purpose in nature. Simplicius, writing in the 6th century AD, is the most comprehensive of all the commentators. He reports interpretations of Aristotle from the preceding 800 years by Eudemus, Posidonius, Porphyry and Syranius. His accounts of the various definitions of nature and of chance are highly useful, are as his analyses of Aristotle's technical terms, per accidens and privation. He often carries out the project, which Aristotle himself proposed but never undertook, of putting Aristotle's scientific explanations into syllogistic form.

Chapters 5 and 6 of Aristotle's Categories describe his first two categories, Substance and Quantity. It is usually taken that Plotinus attacked Aristotle's Categories, but that Porphyry and Iamblichus restored it to the curriculum once and for all. Nonetheless, the introduction to this text stresses how much of the defence of Aristotle Porphyry was able to draw out of Plotinus' critical discussion. Simplicius' commentary is our most comprehensive account of the debate on the validity of Aristotle's Categories. One subject discussed by Simplicius in these chapters is where the differentia of a species (eg the rationality of humans) fits into the scheme of categories. Another is why Aristotle elevates the category of Quantity to second place, above the category of Quality. Further, de Haas shows how Simplicius distinguishes different kinds of universal order to solve some of the problems.

Book 2 of the "Physics" is arguably the best introduction to Aristotle's ideas, as well as being the most interesting and representative book in the whole of his corpus. It defines nature and distinguishes natural science from mathematics. It introduces the seminal idea of four causes, or four modes of explanation. It defines chance, but rejects a theory of chance and natural selection in favour of purpose in nature. Simplicius, writing in the sixth century AD, adds his own considerable contribution to this work. Seeing Aristotle's God as a Creator, he discusses how nature relates to soul, adds Stoic and Neoplatonist causes to Aristotle's list of four, and questions the likeness of cause to effect. He discusses missing a great evil or a great good by a hairsbreadth and considers whether animals act from reason or natural instinct. He also preserves a Posidonian discussion of mathematical astronomy.

In "Categories" chapters 7 and 8 Aristotle considers his third and fourth categories - those of Relative and Quality. Critics of Aristotle had suggested for each of the non-substance categories that they could really be reduced to relatives, so it is important how the category of Relative is defined. Aristotle offers two definitions, and the second, stricter, one is often cited by his defenders in order to rule out objections. The second definition of relative involves the idea of something changing its relationship through a change undergone by its correlate, not by itself. There were disagreements as to whether this was genuine change, and Plotinus discussed whether relatives exist only in the mind, without being real. The terms used by Aristotle for such relationships was 'being disposed relatively to something', a term later borrowed by the Stoics for their fourth category, and perhaps originating in Plato's Academy. In his discussion of Quality, Aristotle reports a debate on whether justice admits of degrees, or whether only the possession of justice does so. Simplicius reports the further development of this controversy in terms of whether justice admits a range or latitude (platos). This debate helped to inspire the medieval idea of latitude of forms, which goes back much further than is commonly recognised - at least to Plato and Aristotle.