  According to Simplicius, a 6th century C.E. neo-Platonist commentator on Aristotle, and our main source for the fragments, Anaxagoras began his book by describing an original state of complete (but not entirely uniform) mixture of all the ingredients of the cosmos; that mixture is then set in motion by the action of Mind/Intellect (nous). The ingredients are eternal and always remain in a mixture of all with all, yet the rotary motion produces shifts in the proportions of the ingredients in a given region. The expanding rotation of the original mixture ultimately produces the continuing development of the world as we now perceive it. The foundations of his theory, descriptions of this development, and a discussion of nous form the bulk of what remains to us of Anaxagoras’ book. The testimonia suggest that the book also included detailed accounts of astronomical, meteorological, and geological phenomena as well as more detailed discussions of perception and knowledge, now missing from our collection of fragments, and known only by later reports and criticisms.