Two points remain to be considered: 1st, the connection between the first and second parts of the dialogue; 2ndly, the relation of the “Parmenides” to the other dialogues.
I. In both divisions of the dialogue the principal speaker is the same, and the method pursued by him is also the same, being a criticism on received opinions: first, on the doctrine of Ideas; secondly, of Being. From the Platonic Ideas we naturally proceed to the Eleatic One or Being which is the foundation of them. They are the same philosophy in two forms, and the simpler form is the truer and deeper. For the Platonic Ideas are mere numerical differences, and the moment we attempt to distinguish between them, their transcendental character is lost; ideas of justice, temperance, and good, are really distinguishable only with reference to their application in the world. If we once ask how they are related to individuals or to the ideas of the divine mind, they are again merged in the aboriginal notion of Being. No one can answer the questions which Parmenides asks of Socrates. And yet these questions are asked with the express acknowledgment that the denial of ideas will be the destruction of the human mind. The true answer to the difficulty here thrown out is the establishment of a rational psychology; and this is a work which is commenced in the “Sophist.” Plato, in urging the difficulty of his own doctrine of Ideas, is far from denying that some doctrine of Ideas is necessary, and for this he is paving the way.
In a similar spirit he criticizes the Eleatic doctrine of Being, not intending to deny Ontology, but showing that the old Eleatic notion, and the very name “Being,” is unable to maintain itself against the subtleties of the Megarians. He did not mean to say that Being or Substance had no existence, but he is preparing for the development of his later view, that ideas were capable of relation. The fact that contradictory consequences follow from the existence or nonexistence of one or many, does not prove that they have or have not existence, but rather that some different mode of conceiving them is required. Parmenides may still have thought that “Being was,” just as Kant would have asserted the existence of “things in themselves,” while denying the transcendental use of the Categories.
Several lesser links also connect the first and second parts of the dialogue: (1) The thesis is the same as that which Zeno has been already discussing: (2) Parmenides has intimated in the first part, that the method of Zeno should, as Socrates desired, be extended to Ideas: (3) The difficulty of participating in greatness, smallness, equality is urged against the Ideas as well as against the One.
II. The “Parmenides” is not only a criticism of the Eleatic notion of Being, but also of the methods of reasoning then in existence, and in this point of view, as well as in the other, may be regarded as an introduction to the “Sophist.” Long ago, in the “Euthydemus,” the vulgar application of the “both and neither” Eristic had been subjected to a similar criticism, which there takes the form of banter and irony, here of illustration.
The attack upon the Ideas is resumed in the “Philebus,” and is followed by a return to a more rational philosophy. The perplexity of the One and Many is there confined to the region of Ideas, and replaced by a theory of classification; the Good arranged in classes is also contrasted with the barren abstraction of the Megarians. The war is carried on against the Eristics in all the later dialogues, sometimes with a playful irony, at other times with a sort of contempt. But there is no lengthened refutation of them. The “Parmenides” belongs to that stage of the dialogues of Plato in which he is partially under their influence, using them as a sort of “critics or diviners” of the truth of his own, and of the Eleatic theories. In the “Theaetetus” a similar negative dialectic is employed in the attempt to define science, which after every effort remains undefined still. The same question is revived from the objective side in the “Sophist”: Being and Not-being are no longer exhibited in opposition, but are now reconciled; and the true nature of Not-being is discovered and made the basis of the correlation of ideas. Some links are probably missing which might have been supplied if we had trustworthy accounts of Plato’s oral teaching.
To sum up: the “Parmenides” of Plato is a critique, first, of the Platonic Ideas, and secondly, of the Eleatic doctrine of Being. Neither are absolutely denied. But certain difficulties and consequences are shown in the assumption of either, which prove that the Platonic as well as the Eleatic doctrine must
