 References will be to the primary sources; the two most recent collections of the fragments (Isnardi Parente 1980, Tarán 1981) have indices that will enable the reader to locate the texts (Lang 1911 does not). Citations from Plato and Aristotle are to any standard edition; those from other ancient authors are taken from texts listed in the bibliography (translations are in all cases my own, but where an alternative English translation is available, I have given a reference to it).