§ 2. Beyond these allusions we get comparatively little light from Plato as to the teachings of his predecessors. Xenophanes is once spoken of as the founder of the Eleatic school and of its doctrine of unity. Parmenides is a far more interesting character to Plato, and the highest regard is expressed for him.[101] When his position as to the unity of being and the non-existence of not-being is discussed, there is no reason to think that his opinions are not correctly given; but when Parmenides is introduced as a speaker, we are not to believe that he states the opinions of the real Parmenides any more than the Platonic Sokrates states the positions of the real Sokrates. Of Zeno we learn that he was skilled in the art of dialectic.[102] Zeno’s statement of the occasion and purpose of his book[103] is of course Plato’s deduction from the book itself. The speculations of Anaxagoras are several times mentioned.[104] The statement that he regarded the heavenly bodies as ‘λίθοι’ is a welcome addition to our knowledge of his doctrines; and Plato’s criticism of Anaxagoras’ use of his fundamental principle is most important. Of Empedokles we hear but little; the statement of his doctrine of sense-perception is a happy exception to the rule. The accuracy of Plato’s statements where they can be tested gives an added importance to what he says about the Pythagoreans.[105] In a word all the data which we have from Plato are valuable, but these data are much fewer than we might expect. § 3. Both the citations from earlier philosophers and the statement of their opinions are much more frequent in the writings of Aristotle. Two of his references to the sayings of Herakleitos are not new to the reader of Plato; indeed Fr. 41 _ap._ Meta. 1010 a 13 is cited with direct reference to the passage where it is cited in Plato. Fr. 37, if we may accept the conjecture of Patin,[106] is a sarcastic phrase of Herakleitos which Aristotle has introduced seriously into a theory of sense-perception. Fr. 46 and 57 are summary phrases stating the fundamental positions of Herakleitos; Fr. 51 and 55 proverbial sayings attributed to him; Fr. 59 alone has the form of a genuine quotation.[107] It is evident that summary phrases give the philosopher’s impression, just as proverbial sayings may come through the medium of popular thought, so that neither have quite the value of direct quotation. From Xenophanes Aristotle gives two _mots_, which were attributed naturally enough to the poet-skeptic. There is no proof that Xenophanes was the original author of either of them.