Euclid, Elements
Thomas L. Heath, Sir Thomas Little Heath, Ed.

It is of course evident that Proclus had before him the original works of Plato, Aristotle, Archimedes and Plotinus, as well as the Συμμικτά of Porphyry and the works of his master Syrianus (ὁ ἡμέτερος καθηγεμών）², from whom he quotes in his note on the definition of an angle. Tannery also points out that he must have had before him a group of works representing the Pythagorean tradition on its mystic, as distinct from its mathematical, side, from Philolaus downwards, and comprising the more or less apocryphal ἱερὸς λόγος of Pythagoras, the Oracles (λόγια), and Orphic verses³.

Besides quotations from writers whom we can identify with more or less certainty, there are many other passages which are doubtless quoted from other commentators whose names we do not know. A list of such passages is given by van Pesch⁴, and there is no need to cite them here.

Van Pesch also gives at the end of his work⁵ a convenient list of the books which, as the result of his investigation, he deems to have been accessible to and directly used by Proclus. The list is worth giving here, on the same ground of convenience. It is as follows: “Eudemus: history of geometry. Geminus: the theory of the mathematical sciences. Heron: commentary on the Elements of Euclid. Porphyry: commentary on the Elements of Euclid. Pappus: commentary on the Elements of Euclid. Apollonius of Perga: a work relating to elementary geometry. Ptolemy: on the parallel-postulate. Posidonius: a book controverting Zeno of Sidon. Carpus: astronomy. Syrianus: a discussion on the angle. Pythagorean philosophical tradition. Plato's works. Aristotle's works. Archimedes' works. Plotinus: Enneades.”

Lastly we come to the question what passages, if any, in the commentary of Proclus represent his own contributions to the subject. As we have seen, the onus probandi must be held to rest upon him who shall maintain that a particular note is original on the part of Proclus. Hence it is not enough that it should be impossible to point to another writer as the probable source of a note; we must have a positive reason for attributing it to Proclus. The criterion must therefore be found either (1) in the general terms in which Proclus points out the deficiencies in previous commentaries and indicates the respects in which his own will differ from them, or (2) in specific expressions used by him in introducing particular notes which may