Parmenides is fascinating as a penetrating criticism of the theory of ideas, or forms, in its undeveloped state, as propounded by the youthful Socrates. According to the report given by Antiphon—a report of the conversation between Parmenides and Socrates, with some assistance from Zeno and Aristoteles—Socrates met Parmenides when the latter was about sixty-five years old and famous for his poem Peri physes (fifth century b.c.e.; The Fragments of Parmenides, 1869; commonly known as On Nature), in which he argued, with great ingenuity, that “All is one.” It may very well be that this conversation occurred as reported, but what is more likely is that Plato, having heard that at one time young Socrates met the aging Parmenides, used this bit of historical information as a dramatic center about which to build a summary of Parmenidean criticism of his theory of ideas, taking some of the edge off the criticism by portraying Socrates as clever but immature in his thinking. Consequently, Parmenides serves as evidence that Plato was never entirely satisfied with the theory of ideas. Like all great philosophers, he kept coming back to his central thesis, subjecting it to critical scrutiny and modifying it in accordance with the discoveries of its weaknesses.
The presentation of the dialogue is somewhat complicated. Cephalus repeats an account originally given by Antiphon of the meeting between Parmenides and Socrates. The actual conversation presumably occurred several years earlier.
Socrates had gone with others to hear the writings of Zeno, who was visiting Athens with Parmenides. After hearing Zeno read from some of his writings, Socrates summed up Zeno’s thesis as stating that “if being is many, it must be both like and unlike, and . . . this is impossible.” The youthful Socrates then pointed out that this was simply a roundabout way of supporting Parmenides’ doctrine that all is one, for to claim that Being is not many and to state that it is one is to make one and the same claim.
Zeno agreed with Socrates, but he defended himself by saying that his argument was designed to show the inconsistency in upholding the doctrine that Being is not one, but many.
Socrates then professed not to see the extraordinariness of saying that things could be both like and unlike. It would be paradoxical, he agreed, to say in regard to the idea of likeness that it could somehow partake of unlikeness; after all, the likeness that things might share could not in itself, as an absolute nature, be unlikeness. However, things—as distinguished from absolute ideas, or natures—could very well be alike in some respect or to some degree and unlike in some other respect or degree. To say that things are one simply because it is possible to speak of them as partaking of the idea oneness, while at the same time they might, in some other respect, partake of the idea of the many, is only to utter a truism. The impression left by Socrates’ argument was that the view held by Parmenides and Zeno might very well be trivial, nothing but a truism.
Apparently both Parmenides and Zeno were upset and impressed by Socrates’ criticism, but the venerable Parmenides had no intention of allowing Socrates to escape scrutiny of his own views. He began to probe Socrates’ distinction between ideas in themselves (or kinds of things) and things of certain kinds (partaking of ideas). He drew from Socrates the admission that Socrates believed in ideas (such as the idea of likeness), which can be considered as distinct from that which partakes of the ideas. Socrates emphatically asserted that there are absolute ideas of the just, the beautiful, the good, and such matters, but he was not certain that there are ideas of man, fire, and water—and he was certain that there are no absolute ideas of such vile materials as hair, mud, and dirt. Nevertheless, Socrates did admit that he sometimes thought that there is an idea of everything—that even the most vile things partake of absolute...
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