 For four reasons it is difficult to pinpoint Ammonius’ own philosophical positions and contributions to philosophy or to the interpretation of Aristotle: (1) Our evidence is confined to commentaries on Aristotle, whose interpretation did not leave as much scope for expounding Neoplatonic ideas as did that of Plato. (2) He depends in these works on Proclus, whose Aristotle lectures or commentaries do not survive, so that we cannot be sure what in them is really his own. (3) Some of Ammonius’ works failed to reach us. (4) We have to depend to a significant degree on his pupils’ writings for our information about him and his contributions, and their own stance may be difficult to separate from that of Ammonius himself. The best approach at present attempts to piece together Ammonius’ views from his commentary on De Interpretatione, from statements attributed to him by later commentators, and from those lectures of Ammonius which were either published by students under Ammonius’ name or which, while published under students’ names, seem to show little sign of having altered his teachings—namely, Asclepius on the Metaphysics and the early commentaries of Philoponus (or their early versions, in the case of commentaries, such as that on the Physics, which were revised). The use of Philoponus to recover Ammonius’ positions was much advanced by Verrycken 1990a; his chronology of the commentaries by Philoponus—and hence, the degree to which they may represent the thought of Ammonius, before Philoponus departed from it in important ways—has recently been revisited by Golitsis 2008 and Sorabji 2016d. (see above, sect. 1.2).