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.