[Footnote 447: Lewes's "Biographical History of Philosophy," p. 38; Ritter's "History of Ancient Philosophy," vol. i. pp. 428, 429.] [Footnote 448: Ritter's "History of Ancient Philosophy," vol. i. pp. 432, 434.] [Footnote 449: Butler's "Lectures," vol. i. p. 331, note; Ritter's "History of Ancient Philosophy," vol. i. p. 428.] _Parmenides of Elea_ (born B.C. 536) was the philosopher who framed the psychological opinions of the Idealist school into a precise and comprehensive system. He was the first carefully to distinguish between _Truth_ (ἀλήθειαν) and _Opinion_ (δοξαν)--between ideas obtained through the reason and the simple perceptions of sense. Assuming that reason and sense are the only sources of knowledge, he held that they furnish the mind with two distinct classes of cognitions--one variable, fleeting, and uncertain; the other immutable, necessary, and eternal. Sense is dependent on the variable organization of the individual, and therefore its evidence is changeable, uncertain, and nothing but a mere "_seeming_." Reason is the same in all individuals, and therefore its evidence is constant, real, and true. Philosophy is, therefore, divided into two branches--_Physics_ and _Metaphysics_; one, a science of absolute knowledge; the other, a science of mere appearances. The first science, Physics, is pronounced illusory and uncertain; the latter, Metaphysics, is infallible and immutable.[450] Proceeding on these principles, he rejects the dualistic system of the universe, and boldly declared that all essences are fundamentally _one_--that, in fact, there is no real plurality, and that all the diversity which "appears" is merely presented under a peculiar aesthetic or sensible law. The senses, it is true, teach us that there are "many things," but reason affirms that, at bottom, there exists only "the one." Whatever, therefore, manifests itself in the field of sense is merely illusory--the mental representation of a phenomenal world, which to experience seems diversified, but which reason can not possibly admit to be other than "immovable" and "one." There is but one Being in the universe, eternal, immovable, absolute; and of this unconditioned being all phenomenal existences, whether material or mental, are but the attributes and modes. Hence the two great maxims of the Eleatic school, derived from Parmenides--τὰ πάντα ἕν, "_The All is One_" and τὸ αὐτὸ νοεῖν τε καὶ εἶναι (Idem est cogitare atque esse), "_Thought and Being are identical._" The last remarkable dictum is the fundamental principle of the modern pantheistic doctrine of "absolute identity" as taught by Schelling and Hegel.[451] [Footnote 450: Ritter's "History of Ancient Philosophy," vol. i. pp. 447, 451.] [Footnote 451: Id., ib., vol. i. pp. 450, 455.]