27 Plato, Sophistes, pp. 247-248.

The view taken of this matter by Mr. John Stuart Mill, in the third chapter of the first Book of his System of Logic, is very instructive; see especially pp. 65-66 (ed. 4th).

Aristippus (one of the Sokratici viri, contemporary of Plato) and the Kyrenaic sect affirmed the doctrine — ὅτι μόνα τὰ πάθη καταληπτά. Aristokles refutes them by saying that there can be no πάθος without both Object and Subject — ποιοῦν and πάσχον. And he goes on to declare that these three are of necessary co-existence or consubstantiality. Ἀλλὰ μὴν ἀνάγκη γε τρία ταῦτα συνυφίστασθαι — τό τε πάθος αὐτό, καὶ τὸ ποιοῦν, καὶ τὸ πάσχον (ap. Eusebium, Præp. Ev. xiv. 19, 1).

I apprehend that Aristokles by these words does not really refute what Aristippus meant to affirm. Aristippus meant to affirm the Relative, and to decline affirming anything beyond; and in this Aristokles agrees, making the doctrine even more comprehensive by showing that Object as well as Subject are relative also; implicated both with each other and in the πάθος.

28 Plato, Theætêt. p. 152 D.

Though Plato states the grounds of this theory in his ironical way, as if it were an absurd fancy, yet it accidentally coincides with the largest views of modern physical science. Absolute rest is unknown in nature: all matter is in perpetual movement, molecular as well as in masses.

29 Plato, Theætêt. pp. 153-154. ὃ δὴ ἕκαστον εἶναί φαμεν χρῶμα, οὔτε τὸ προσβάλλον οὔτε τὸ προσβαλλόμενον ἔσται, ἀλλὰ μεταξύ τι ἑκαστῳ ἴδιον γεγονός.

30 Plato, Theætêt. pp. 154-155. Compare the reasoning in the Phædon, pp. 96-97-101.

31 The Aristotelian Category of Relation (τὰ πρὸς τί, Categor. p. 6, a. 36) designates one object apprehended and named relatively to some other object — as distinguished from object apprehended and named not thus relatively, which Aristotle considers as per se καθ’ αὑτό (Ethica Nikomach. i. p. 1096, a. 21). Aristotle omits or excludes relativity of the object apprehended to the percipient or concipient subject, which is the sort of relativity directly noted by the Protagorean doctrine.

Occasionally Aristotle passes from relativity in the former sense to relativity in the latter; as when he discusses ἐπιστητὸν and ἐπιστήμη, alluded to in one of my former notes on this dialogue. But he seems unconscious of any transition. In the Categories, Object, as implicated with Subject does not seem to have been distinctly present to his reflection. In the third book of the Metaphysica, indeed, he discusses professedly the opinion of Protagoras; and among his objections against it, one is, that it makes everything relative or πρὸς τί (Metaph. Γ. p. 1011, a. 20, b. 5). This is hardly true in the sense which πρὸς τί bears as one of his Categories: but it is true in the other sense to which I have adverted.

A clear and full exposition of what is meant by the Relativity of Human Knowledge, will be found in Mr. John Stuart Mill’s most recent work, ‘Examination of Sir William Hamilton’s Philosophy,’ ch. ii. pp. 6-15.

32 Plato, Theætêt. p. 156 A. ὡς τὸ πᾶν κίνησις ἦν, καὶ ἄλλο παρὰ τοῦτο οὐδέν, τῆς δὲ κινήσεως δύο εἴδη, πλήθει μὲν ἄπειρον ἑκάτερον, δύναμιν δὲ τὸ μὲν ποιεῖν ἔχον, τὸ δὲ πάσχειν. Ἐκ δὲ τῆς τούτων ὁμιλίας τε καὶ τρίψεως πρὸς ἄλληλα γίγνεται ἔκγονα πλήθει μὲν ἄπειρα, δίδυμα δέ — τὸ μὲν αἰσθητόν, τὸ δὲ αἴσθησις, ἀεὶ συνεκπίπτουσα καὶ γεννωμένη μετὰ τοῦ αἰσθητοῦ.

33 Plato, Theætêt. p. 156 B.

34 Plato, Theætêt. p. 156 E. ὁ μὲν ὀφθαλμὸς ἄρα ὄψεως ἔμπλεως ἐγένετο καὶ ὁρᾷ δὴ τότε καὶ ἐγένετο οὔ τι ὄψις ἀλλὰ ὀφθαλμὸς ὁρῶν, τὸ δὲ ξυγγεννῆσαν τὸ χρῶμα λευκότητος περιεπλήσθη καὶ ἐγένετο οὐ λευκότης αὖ ἀλλὰ λευκόν, εἴτε ξύλον εἴτε λίθος εἴτε ὁτιοῦν ξυνέβη χρῆμα χρωσθῆναι τῷ τοιούτῳ χρώματι.

Plato’s conception of the act of vision was — That fire darted forth from the eyes of the percipient and came into confluence or coalescence with fire approaching from the perceived object (Plato, Timæus, pp. 45 C, 67 C).

35 Plato, Theætêt. p. 157 A. ἐπεὶ καὶ τὸ ποιοῦν εἶναι τι καὶ τὸ πάσχον αὖ τι ἐπὶ ἑνὸς νοῆσαι, ὥς φασιν, οὐκ εἶναι παγίως. Οὔτε γὰρ ποιοῦν ἐστί τι, πρὶν ἂν τῷ πάσχοντι ξυνέλθῃ — οὔτε πάσχον, πρὶν ἂν τῷ ποιοῦντι, &c.

36 Plato, Theætêt. p. 157 A. τό τέ τινι ξυνελθὸν καὶ ποιοῦν ἄλλῳ αὖ προσπεσὸν πάσχον ἀνεφάνη.

37 Plato, Theætêt. p. 157 A. οὐδὲν εἶναι ἓν αὐτὸ καθ’ αὑτό, ἀλλά τινι ἀεὶ γίγνεσθαι, τὸ δ’ εἶναι παντάχοθεν ἐξαιρετέον, &c.

38 Plato, Theætêt. p. 157 B. δεῖ δὲ καὶ κατὰ μέρος οὕτω λέγειν καὶ περὶ πολλῶν ἀθροισθέντων, ᾧ δὴ ἀθροίσματι ἄνθρωπόν τε τίθενται καὶ λίθον καὶ ἕκαστον ζῶόν τε καὶ εἶδος.

In this passage I follow Heindorf’s explanation which seems dictated by the last word εἶδος. Yet I am not sure that Plato does really mean here the generic aggregates. He had before talked about sights, sounds, hot, cold, hard, &c., the separate sensations. He may perhaps here mean simply individual things as aggregates or ἀθροίσματα — a man, a stone, &c.

39 Plato, Theætêt. p. 157 E.

40 Plato, Theætêt. p. 159.

41 Plato, Theætêt. p. 160 A.

42 Plato, Theætêt. p. 160 B. ἔπειπερ ἡμῶν ἡ ἀνάγκη τὴν οὐσίαν συνδεῖ μέν, συνδεῖ δε οὐδενὶ τῶν ἄλλων, οὐδ’ αὖ ἡμῖν αὐτοῖς· ἀλλήλοις δὴ λείπεται συνδεδέσθαι (i. e. τὸν αἰσθανόμενον and τὸ ποιοῦν αἰσθάνεσθαι). Ὤστε εἴτε τις εἶναι τί ὀνομάζει, τινὶ εἶναι, ἢ τινός, ἢ πρός τι, ῥητέον αὐτῷ, εἴτε γίγνεσθαι· αὐτὸ δὲ ἐφ’ αὑτοῦ τι ἢ ὂν ἢ γιγνόμενον οὔτε αὐτῷ λεκτέον, οὔτ’ ἄλλου λέγοντος ἀποδεκτέον.

Compare Aristot. Metaphys. Γ. 6, p. 1011, a. 23.

43 Aristotle, in a passage of the treatise De Animâ (iii. 1, 2-4-7-8, ed. Trendelenburg, p. 425, b. 25, p. 426, a. 15-25, Bekk.), impugns an opinion of certain antecedent φυσιόλογοι whom he does not specify; which opinion seems identical with the doctrine of Protagoras. These philosophers said, that “there was neither white nor black without vision, nor savour without the sense of taste”. Aristotle says that they were partly right, partly wrong. They were right in regard to the actual, wrong in regard to the potential. The actual manifestation of the perceived is one and the same with that of the percipient, though the two are not the same logically in the view of the reflecting mind (ἡ δὲ τοῦ αἰσθητοῦ ἐνέργεια καὶ τῆς αἰσθήσεως ἡ αὐτὴ μέν ἐστι καὶ μία, τὸ δ’ εἶναι οὐ ταὐτὸν αὐταῖς). But this is not true when we speak of them potentially — διχῶς γὰρ λεγομένης τῆς αἰσθήσεως καὶ τοῦ αἰσθητοῦ, τῶν μὲν κατὰ δύναμιν τῶν δὲ κατ’ ἐνέργειαν, ἐπί τούτων μὲν συμβαίνει τὸ λεχθέν, ἐπὶ δὲ τῶν ἑτέρων οὐ συμβαίνει. Ἀλλ’ ἐκεῖνοι ἁπλῶς ἔλεγον περὶ τῶν λεγομένων οὐχ ἁπλῶς.

I think that the distinction, which Aristotle insists upon as a confutation of these philosophers, is not well founded. What he states, in very just language, about actual perception is equally true about potential perception. As the present fact of actual perception implicates essentially a determinate percipient subject with a determinate perceived object, and admits of being looked at either from the one point of view or from the other — so the concept of potential perception implicates in like manner an indeterminate perceivable with an indeterminate subject competent to perceive. The perceivable or cogitable has no meaning except in relation to some Capax Percipiendi or Capax Cogitandi.

44 The terms Ego and Mecum, to express the antithesis of these two λόγῳ μόνον χωριστὰ, are used by Professor Ferrier in his very acute treatise, the Institutes of Metaphysic, pp. 93-96. The same antithesis is otherwise expressed by various modern writers in the terms Ego and non-Ego — le moi et le non-moi. I cannot think that this last is the proper way of expressing it. You do not want to negative the Ego, but to declare its essential implication with a variable correlate; to point out the bilateral character of the act of consciousness. The two are not merely Relata secundum dici but Relata secundum esse, to use a distinction recognised in the scholastic logic.

The implication of Subject and Object is expressed in a peculiar manner (though still clearly) by Aristotle in the treatise De Animâ, iii. 8, 1, 431, b. 21. ἡ ψυχὴ τὰ ὄντα πώς ἐστι πάντα· ἢ γὰρ αἰσθητὰ τὰ ὄντα ἢ νοητά. ἐστὶ δ’ ἡ ἐπιστήμη μὲν τὰ ἐπιστητά πως, ἡ δ’ αἴσθησις τὰ αἰσθητά. The adverb πως (τρόπον τινά, as Simplikius explains it, fol. 78, b. 1) here deserves attention. “The soul is all existing things in a certain way (or looked at under a certain aspect). All things are either Percepta or Cogitata: now Cognition is in a certain sense the Cognita — Perception is the Percepta.” He goes on to say that the Percipient Mind is the Form of Percepta, while the matter of Percepta is without: but that the Cogitant Mind is identical with Cogitata, for they have no matter (iii. 4, 12, p. 430, a. 3, with the commentary of Simplikius p. 78, b. 17, f. 19, a. 12). This is in other words the Protagorean doctrine — That the mind is the measure of all existences; and that this is even more true about νοητὰ than about αἰσθητά. That doctrine is completely independent of the theory, that ἐπιστήμη is αἴσθησις.

It is in conformity with this affirmation of Aristotle (partially approved even by Cudworth — see Mosheim’s Transl. of Intell. Syst. Vol. II. ch. viii. pp. 27-28) — ἡ ψυχὴ τὰ ὄντα πώς ἐστι πάντα — that Mr. John Stuart Mill makes the following striking remark about the number of ultimate Laws of Nature:—

“It is useful to remark, that the ultimate Laws of Nature cannot possibly be less numerous than the distinguishable sensations or other feelings of our nature: those, I mean, which are distinguishable from one another in quality, and not merely in quantity or degree. For example, since there is a phenomenon sui generis called colour, which our consciousness testifies to be not a particular degree of some other phenomenon, as heat, or odour, or motion, but intrinsically unlike all others, it follows that there are ultimate laws of colour …The ideal limit therefore of the explanation of natural phenomena would be to show that each distinguishable variety of our sensations or other states of consciousness has only one sort of cause.” (System of Logic, Book iii. ch. 14, s. 2.)

45 The elaborate Dissertation of Sir William Hamilton, on the Philosophy of the Unconditioned (standing first in his ‘Discussions on Philosophy’), is a valuable contribution to metaphysical philosophy. He affirms and shows, “That the Unconditioned is incognisable and inconceivable: its notion being only a negation of the Conditioned, which last can alone be positively known and conceived” (p. 12); refuting the opposite doctrine as proclaimed, with different modifications, both by Schelling and Cousin.

In an Appendix to this Dissertation, contained in the same volume (p. 608), Sir W. Hamilton not only re-asserts the doctrine (“Our whole knowledge of mind and matter is relative, conditioned — relatively conditioned. Of things absolutely or in themselves, be they external, be they internal, we know nothing, or know them only as incognisable,” &c.) — but affirms farther that philosophers of every school, with the exception of a few late absolute theorisers in Germany, have always held and harmoniously re-echoed the same doctrine.

In proof of such unanimous agreement, he cites passages from seventeen different philosophers.

The first name on his list stands as follows:— “1. Protagoras — (as reported by Plato, Aristotle, Sextus Empiricus, Diogenes Laertius, &c.) — Man is (for himself) the measure of all things”.

Sir William Hamilton understands the Protagorean doctrine as I understand it, and as I have endeavoured to represent it in the present chapter. It has been very generally misconceived.

I cannot, however, agree with Sir William Hamilton, in thinking that this theory respecting the Unconditioned and the Absolute, has been the theory generally adopted by philosophers. The passages which he cites from other authors are altogether insufficient to prove such an affirmation.

46 Plato, Theætêt. p. 156 A. τῆς δὲ κινήσεως δύο εἴδη, πλήθει μὲν ἄπειρον ἑκάτερον, δύναμιν δὲ τὸ μὲν ποιεῖν ἔχον, τὸ δὲ πάσχειν.

47 In that distinction, upon which Aristotle lays so much stress, between Actus and Potentia, he declares Actus or actuality to be the Prius — Potentia or potentiality to be the Posterius. See Metaphysica, Θ. 8, 1049, b. 5 seqq.; De Animâ, ii. 4, 415, a. 17. The Potential is a derivative from the Actual — derived by comparison, abstraction, and logical analysis: a Mental concept, helping us to describe, arrange, and reason about, the multifarious acts of sense or consciousness — but not an anterior generating reality.

Turgot observes (Œuvres, vol. iii. pp. 108-110; Article in the Encyclopédie, Existence):—

“Le premier fondement de la notion de l’existence est la conscience de notre propre sensation, et le sentiment du moi qui résulte de cette conscience. La relation nécessaire entre l’être appercevant, et l’être apperçu considéré hors du moi, suppose dans les deux termes la même réalité. Il y a dans l’un et dans l’autre un fondement de cette relation, que l’homme, s’il avoit un langage, pourroit désigner par le nom commun d’existence ou de présence: car ces deux notions ne seroient point encore distinguées l’une de l’autre.…

“Mais il est très-important d’observer que ni la simple sensation des objets présens, ni la peinture que fait l’imagination des objets absens, ni le simple rapport de distance ou d’activité réciproque, commun aux uns et aux autres, ne sont précisément la chose que l’esprit voudroit désigner par le nom général d’existence; c’est le fondement même de ces rapports, supposé commun au moi, à l’objet vu et à l’objet simplement distant, sur lequel tombe véritablement et le nom d’existence et notre affirmation, lorsque nous disons qu’une chose existe. Ce fondement n’est ni ne peut être connu immédiatement, et ne nous est indiqué que par les rapports différents qui le supposent: nous nous en formons cependant une espèce d’idée que nous tirons par voie d’abstraction du témoignage que la conscience nous rend de nous-mêmes et de notre sensation actuelle: c’est-à-dire, que nous transportons en quelque sorte cette conscience du moi sur les objets extérieurs, par une espèce d’assimilation vague, démentie aussitôt par la séparation de tout ce qui caractérise le moi, mais qui ne suffit pas moins pour devenir le fondement d’une abstraction ou d’un signe commun, et pour être l’objet de nos jugemens.”