Now apply this to the case of cognition. The Form of Cognition correlates exclusively with the Form of Truth: the Form of each special Cognition, geometrical or medical, or other, correlates with the Form of Geometry or Medicine. But Cognition as we possess it, correlates only with Truth relatively to us: also, each special Cognition of ours has its special correlating Truth, relatively to us.[19] Now the Forms are not in or with us, but apart from us: the Form of Cognition is not our Cognition, the Form of Truth is not our Truth. Forms can be known only through the Form of Cognition, which we do not possess: we cannot therefore know Forms. We have our own cognition, whereby we know what is relative to us; but we know nothing more. Forms, which are not relative to us, lie out of our knowledge. Bonum per se, Pulchrum per se, and the other self-existent Forms or Ideas, are to us altogether unknowable.[20]
[19] Plato, Parmenid. p. 134 A. Οὐκοῦν καὶ ἐπιστήμη, αὐτὴ μὲν ὃ ἔστιν ἐπιστήμη, τῆς ὃ ἔστιν ἀλήθεια, αὐτῆς ἂν ἐκείνης εἴη ἐπιστήμη; … Ἡ δὲ παρ’ ἡμῖν ἐπιστήμη οὐ τῆς παρ’ ἡμῖν ἂν ἀληθείας εἴη; καὶ αὖ ἑκάστη ἡ παρ’ ἡμῖν ἐπιστήμη τῶν παρ’ ἡμῖν ὄντων ἑκάστου ἂν ἐπιστήμη σύμβαινοι εἶναι;
Aristotle (Topica, vi. p. 147, a. 6) adverts to this as an argument against the theory of Ideas, but without alluding to the Parmenides; indeed he puts the argument in a different way — τὸ δ’ εἶδος πρὸς τὸ εἶδος δοκεῖ λέγεσθαι, οἷον αὐτὴ ἐπιθυμία αὐτοῦ ἡδέος, καὶ αὐτὴ βούλησις αὐτοῦ ἀγαθοῦ. Aristotle argues that there is no place in this doctrine for the φαινόμενον ἀγαθόν, which nevertheless men often wish for, and he remarks, in the Nikom. Ethica, i. 4, 1096 b. 33 — that the αὐτὸ-ἀγαθὸν is neither πρακτὸν nor κτητὸν ἀνθρώπῳ.
[20] Plato, Parmenid. p. 134 C. Ἄγνωστον ἄρα ἡμῖν καὶ αὐτὸ τὸ καλὸν ὃ ἔστι, καὶ τὸ ἀγαθόν, καὶ πάντα ἃ δὴ ὡς ἰδέας αὐτὰς οὔσας ὑπολαμβάνομεν.
Form of cognition, superior to our Cognition, belongs to the Gods. We cannot know them, nor can they know us.
6. Again, if there be a real self-existent Form of Cognition, apart from that which we or others possess — it must doubtless be far superior in accuracy and perfection to that which we possess.[21] The Form of Beauty and the other Forms, must be in like manner superior to that which is found under the same name in individual objects. This perfect Form of Cognition must therefore belong to the Gods, if it belong to any one. But if so, the Gods must have a Form of Truth, the proper object of their Form of Cognition. They cannot know the truth relatively to us, which belongs to our cognition — any more than we can know the more perfect truth belonging to them. So too about other Forms. The perfect Form of mastership belongs to the Gods, correlating with its proper Form of servantship. Their mastership does not correlate with individual objects like us: in other words, they are not our masters, nor are we their servants. Their cognition, again, does not correlate with individual objects like us: in other words, they do not know us, nor do we know them. In like manner, we in our capacity of masters are not masters of them — we as cognizant beings know nothing of them or of that which they know. They can in no way correlate with us, nor can we correlate with them.[22]
[21] An argument very similar is urged by Aristotle (Metaph. Θ. 1050, b. 34) εἰ ἄρα τινές εἰσι φύσεις τοιαῦται ἢ οὐσίαι οἵας λέγουσιν οἱ ἐν τοῖς λόγοις τὰς ἰδέας, πολὺ μᾶλλον ἐπιστῆμον ἄν τι εἴη ἡ αὐτοεπιστήμη καὶ κινούμενον ἡ κίνησις.
[22] Plato, Parmenid. p. 135 A. Ταῦτα μὲντοι, ὦ Σώκρατες, ἔφη ὁ Παρμενίδης, καὶ ἔτι ἄλλα πρὸς τούτοις πάνυ πολλὰ ἀναγκαῖον ἔχειν τὰ εἴδη, εἰ εἰσὶν αὐται αἱ ἰδέαι τῶν ὄντων, &c.
Sum total of objections against the Ideas is grave. But if we do not admit that Ideas exist, and that they are knowable, there can be no dialectic discussion.
Here are some of the objections, Sokrates (concludes Parmenides), which beset your doctrine, that there exist substantive, self-standing, Forms of Ideas, each respectively definable. Many farther objections might also be urged.[23] So that a man may reasonably maintain, either that none such exist — or that, granting their existence, they are essentially unknowable by us. He must put forth great ingenuity to satisfy himself of the affirmative; and still more wonderful ingenuity to find arguments for the satisfaction of others, respecting this question.