THIS DOCTRINE TAUGHT BY PARMENIDES.
The first philosopher who taught this was Parmenides, who identified Existence and Intelligence, and who does not place existence among sense-objects, "for, thought is the same thing as existence."[246] He adds[247] that existence is immovable, although being thought. Parmenides thus denies all corporeal movement in existence, so as that it might always remain the same. Further, Parmenides[248] compares existence to a sphere, because it contains everything, drawing thought not from without, but from within itself. When Parmenides, in his writings, mentions the One, he means the cause, as if he recognized that this unity (of the intelligible being) implied manifoldness. In the dialogue of Plato he speaks with greater accuracy, and distinguishes three principles: the First, the absolute One; the second, the manifold one; the third, the one and the manifold. He therefore, as we do, reaches three natures.