_Metaph._ i. 5; 986 b 18. For Parmenides seemed to lay hold of a unity according to reason, and Melissos according to matter; wherefore the former says it is limited, the latter that it is unlimited. Xenophanes first taught the unity of things (Parmenides is said to have been his pupil), but he did not make anything clear, nor did he seem to get at the nature of either finiteness or infinity, but, looking up into the broad heavens, he said, the unity is god. These, as we said, are to be dismissed from the present investigation, two of them entirely as being somewhat more crude, Xenophanes and Melissos; but Parmenides seems to speak in some places with greater care. For believing that not-being does not exist in addition to being, of necessity he thinks that being is one and that there is nothing else, ... and being compelled to account for phenomena, and assuming that things are one from the standpoint of reason, plural from the standpoint of sense, he again asserts that there are two causes and two first principles, heat and cold, or, as he calls them, fire and earth; of these he regards heat as being, its opposite as not-being. _Metaph._ ii. 4; 1001 a 32. There is nothing different from being, so that it is necessary to agree with the reasoning of Parmenides that all things are one, and that this is being. (_c_) PASSAGES RELATING TO PARMENIDES IN THE DOXOGRAPHISTS. Theophrastos, Fr. 6; Alexander _Metaph._ p. 24, 5 Bon.; _Dox._ 482. And succeeding him Parmenides, son of Pyres, the Eleatic—Theophrastos adds the name of Xenophanes—followed both ways. For in declaring that the all is eternal, and in attempting to explain the genesis of things, he expresses different opinions according to the two standpoints:—from the standpoint of truth he supposes the all to be one and not generated and spheroidal in form, while from the standpoint of popular opinion, in order to explain generation of phenomena, he uses two first principles, fire and earth, the one as matter, the other as cause and agent. Theophrastos, Fr. 6 a; Laer. Diog. ix. 21, 22; _Dox._ 482. Parmenides, son of Pyres, the Eleatic, was a pupil of Xenophanes, yet he did not accept his doctrines.... He was the first to declare that the earth is spheroidal and situated in the middle of the universe. He said that there are two elements, fire and earth; the one has the office of demiurge, the other that of matter. Men first arose from mud; heat and cold are the elements of which all things are composed. He holds that intelligence and life are the same, as Theophrastos records in his book on physics, where he put down the opinions of almost everybody. He said that philosophy has a twofold office, to understand both the truth and also what men believe. Accordingly he says: (Vv. 28-30), ‘’Tis necessary for thee to learn all things, both the abiding essence of persuasive truth, and men’s opinions in which rests no true belief.’