Also in proclaiming the necessity of specialty of adaptation to individual minds — Plat. Phædr. pp. 271-272, 277 B.
Protagoras did not affirm, that Belief depended upon the will or inclination of each individual but that it was relative to the circumstances of each individual mind.
The grounds of belief, according to Protagoras, relative to the individual, are not the same with all men at all times. But it does not follow (nor does Protagoras appear to have asserted) that they vary according to the will or inclination of the individual. Plato, in impugning this doctrine, reasons as if these two things were one and the same — as if, according to Protagoras, a man believed whatever he chose.[26] This, however, is not an exact representation of the doctrine “Homo Mensura”: which does not assert the voluntary or the arbitrary, but simply the relative as against the absolute. What a man believes does not depend upon his own will or choice: it depends upon an aggregate of circumstances, partly peculiar to himself, partly common to him with other persons more or fewer in number:[27] upon his age, organisation, and temperament — his experience, education, historical and social position — his intellectual powers and acquirements — his passions and sentiments of every kind, &c. These and other ingredients — analogous, yet neither the same nor combined in the same manner, even in different individuals of the same time and country, much less in those of different times and countries — compose the aggregate determining grounds of belief or disbelief in every one. Each man has in his mind an ideal standard of truth and falsehood: but that ideal standard, never exactly the same in any two men, nor in the same man at all times, often varies in different men to a prodigious extent. Now it is to this standard in the man’s own mind that those reasoners refer who maintain that belief is relative. They do not maintain, that it is relative simply to his wishes, or that he believes and disbelieves what he chooses.
[26] Plato, Kratyl. pp. 387-389, where πρὸς ἡμᾶς is considered as equivalent to ὡς ἂν ἡμεῖς βουλώμεθα — ᾗ ἂν ἡμεῖς βουλήθωμεν — both of them being opposed to οἷον ἐπεφύκει — τὸ κατὰ φύσιν — ἰδίαν αὐτῶν φύσιν ἔχουσαι.
The error here noted is enumerated by by Mr. John Stuart Mill, among the specimens of Fallacies of Confusion, in his System of Logic, Book v. ch. vii. § 1: “The following is an argument of Descartes to prove, in his à priori manner, the being of a God. The conception, says he, of an infinite Being proves the real existence of such a Being. For if there is not really any such Being, I must have made the conception: but if I could make it, I can also unmake it — which evidently is not true: therefore there must be, externally to myself, an archetype from which the conception was derived. In this argument (which, it may be observed, would equally prove the real existence of ghosts and of witches) the ambiguity is in the pronoun I; by which, in one place, is to be understood my will — in another, the laws of my nature. If the conception, existing as it does in my mind, had no original without, the conclusion would unquestionably follow that I made it — that is, the laws of my nature must have somehow evolved it: but that my will made it, would not follow. Now when Descartes afterwards adds that I cannot unmake the conception, he means that I cannot get rid of it by an act of my will — which is true, but is not the proposition required. I can as much unmake this conception as I can any other: no conception which I have once had, can I ever dismiss by mere volition: but what some of the laws of my nature have produced, other laws, or those same laws in other circumstances, may, and often do, subsequently efface.”
[27] To show how constantly this Protagorean dictum is misconceived, as if Protagoras had said that things were to each individual what he was pleased or chose to represent them as being, I transcribe the following passage from Lassalle’s elaborate work on Herakleitus (vol. ii. p. 381):— “Des Protagoras Prinzip ist es, dass überhaupt Nichts Objektives ist; dass vielmehr alles Beliebige was Einem scheint, auch für ihn sei. Dies Selbstsetzen des Subjekts ist die einzige Wahrheit der Dinge, welche an sich selbst Nichts Objektives haben, sondern zur gleichgültigen Fläche geworden sind, auf die das Subjekt willkührlich und beliebig seine Charaktere schreibt.”
Protagoras does not (as is here asserted) deny the Objective: he only insists on looking at it in conjunction with, or measured by, some Subject; and that Subject, not simply as desiring or preferring, but clothed in all its attributes.
Facts of sense — some are the same to all sentient subjects, others are different to different subjects. Grounds of unanimity.
When Plato says that combustibility and secability of objects are properties fixed and determinate,[28] this is perfectly true, as meaning that a certain proportion of the facts of sense affect in the same way the sentient and appreciative powers of each individual, determining the like belief in every man who has ever experienced them. Measuring and weighing are sensible facts of this character: seen alike by all, and conclusive proofs to all. But this implies, to a certain point, fundamental uniformity in the individual sentients and judges. Where such condition is wanting — where there is a fundamental difference in the sensible apprehension manifested by different individuals — the unanimity is wanting also. Such is the case in regard to colours and other sensations: witness the peculiar vision of Dalton and many others. The unanimity in the first case, the discrepancy in the second, is alike an aggregate of judgments, each individual, distinct, and relative. You pronounce an opponent to be in error: but if you cannot support your opinion by evidence or authority which satisfies his senses or his reason, he remains unconvinced. Your individual opinion stands good to you; his opinion stands good to him. You think that he ought to believe as you do, and in certain cases you feel persuaded that he will be brought to that result by future experience, which of course must be relative to him and to his appreciative powers. He entertains the like persuasion in regard to you.
[28] When Plato asserts not only that Objects are absolute and not relative to any Subject — but that the agencies or properties of Objects are also absolute — he carries the doctrine farther than modern defenders of the absolute. M. Cousin, in the eighth and ninth Lectures of his Cours d’Hist. de la Philosophie Morale au 18me Siècle, lays down the contrary, maintaining that objects and essences alone are absolute, though unknowable; but that their agencies are relative and knowable.