[100] Plato, Sophist. p. 251 B-C. Compare Plato, Philêbus, p. 14 C.
Misconception of the function of the copula in predication.
This last opinion is said to have been held by Antisthenes, one of the disciples of Sokrates. We do not know how he explained or defended it, nor what reserves he may have admitted to qualify it. Plato takes no pains to inform us on this point. He treats the opinion with derision, as an absurdity. We may conceive it as one of the many errors arising from a misconception of the purpose and function of the copula in predication. Antisthenes probably considered that the copula implied identity between the predicate and the subject. Now the explanation or definition of man is different from the explanation or definition of good: accordingly, if you say, Man is good, you predicate identity between two different things: as if you were to say Two is Three, or Three is Four. And if the predicates were multiplied, the contradiction became aggravated, because then you predicated identity not merely between one thing and another different thing, but between one thing and many different things. The opinion of Antisthenes depends upon two assumptions — That each separate word, whether used as subject or as predicate, denotes a Something separate and existent by itself: That the copula implies identity. Now the first of these two assumptions is not unfrequently admitted, even in the reasonings of Plato, Aristotle, and many others: while the latter is not more remarkable than various other erroneous conceptions which have been entertained, as to the function of the copula.
No formal Grammar or Logic existed at that time. No analysis or classification of propositions before the works of Aristotle.
What is most important to observe is — That at the time which we are here discussing, there existed no such sciences either grammar or formal logic. There was a copious and flexible language — a large body of literature, chiefly poetical — and great facility as well as felicity in the use of speech for the purposes of communication and persuasion. But no attempt had yet been made to analyse or theorise on speech: to distinguish between the different functions of words, and to throw them into suitable classes: to generalise the conditions of good or bad use of speech for proving a conclusion: or to draw up rules for grammar, syntax, and logic. Both Protagoras and Prodikus appear to have contributed something towards this object, and Plato gives various scattered remarks going still farther. But there was no regular body either of grammar or of formal logic: no established rules or principles to appeal to, no recognised teaching, on either topic. It was Aristotle who rendered the important service of filling up this gap. I shall touch hereafter upon the manner in which he proceeded: but the necessity of laying down a good theory of predication, and precepts respecting the employment of propositions in reasoning, is best shown by such misconceptions as this of Antisthenes; which naturally arise among argumentative men yet untrained in the generalities of grammar and logic.
Plato’s declared purpose in the Sophistês — To confute the various schools of thinkers — Antisthenes, Parmenides, the Materialists, &c.
Plato announces his intention, in this portion of the Sophistês, to confute all these different schools of thinkers, to whom he has made allusion.[101] His first purpose, in reasoning against those who maintained Non-Ens to be an incogitable absurdity, is, to show that there are equal difficulties respecting Ens: that the Existent is just as equivocal and unintelligible as the Non-Existent. Those who recognise two co-ordinate and elementary principles (such as Hot and Cold) maintain that both are really existent, and call them both, Entia. Here (argues Plato) they contradict themselves: they call their two elementary principles one. What do they mean by existence, if this be not so?
[101] Plato, Sophist. p. 251 C-D. Ἵνα τοίνυν πρὸς ἅπαντας ἡμῖν ὁ λόγος ᾖ τοὺς πώποτε περὶ οὐσίας καὶ ὁτιοῦν διαλεχθέντας, ἔστω καὶ πρὸς τούτους καὶ πρὸς τοὺς ἄλλους, ὅσοις ἔμπροσθεν διειλέγμεθα, τὰ νῦν ὡς ἐν ἐρωτήσει λεχθησόμενα.
Then again, Parmenides — and those who affirm that Ens Totum was essentially Unum, denying all plurality — had difficulties on their side to surmount. Ens could not be identical with Unum, nor was the name Ens, identical with the thing named Ens. Moreover, though Ens Unum was Totum, yet Totum was not identical with Ens or with Unum. Totum necessarily implied partes: but the Unum per se was indivisible or implied absence of parts. Though it was true therefore that Ens was both Unum and Totum, these two were both of them essentially different from Ens, and belonged to it only by way of adjunct accident. Parmenides was therefore wrong in saying that Unum alone existed.
Plato’s refutation throws light upon the doctrine of Antisthenes.