Sokr. — According to your explanation, then, it is only the temperate man who knows himself. He alone is able to examine himself, and thus to find out what he really knows and does not know: he alone is able to examine others, and thus to find out what each man knows, or what each man only believes himself to know without really knowing. Temperance, or self-knowledge, is the knowledge what a man knows, and what he does not know.[15] Now two questions arise upon this: First, is it possible for a man to know, that he knows what he does know, and that he does not know what he does not know? Next, granting it to be possible, in what way do we gain by it? The first of these two questions involves much difficulty. How can there be any cognition, which is not cognition of a given cognitum, but cognition merely of other cognitions and non-cognitions? There is no vision except of some colour, no audition except of some sound: there can be no vision of visions, or audition of auditions. So likewise, all desire is desire of some pleasure; there is no desire of desires. All volition is volition of some good; there is no volition of volitions: all love applies to something beautiful — there is no love of other loves. The like is true of fear, opinion, &c. It would be singular therefore, if contrary to all these analogies, there were any cognition not of some cognitum, but of itself and other cognitions.[16]
[15] Plato, Charm. 167 A.
[16] Plato, Charm. 167-168.
All knowledge must be relative to some object.
It is of the essence of cognition to be cognition of something, and to have its characteristic property with reference to some correlate.[17] What is greater, has its property of being greater in relation to something else, which is less — not in relation to itself. It cannot be greater than itself, for then it would also be less than itself. It cannot include in itself the characteristic property of the correlatum as well as that of the relatum. So too about what is older, younger, heavier, lighter: there is always a something distinct, to which reference is made. Vision does not include in itself both the property of seeing, and that of being seen: the videns is distinct from the visum. A movement implies something else to be moved: a heater something else to be heated.
[17] Plato, Charm. 168 B. ἔστι μὲν αὑτὴ ἡ ἐπιστήμη τινὸς ἐπιστήμη, καὶ ἔχει τινα τοιαύτην δύναμιν ὥστε τινὸς εἶναι.
All properties are relative — every thing in nature has its characteristic property with reference to something else.
In all these cases (concludes Sokrates) the characteristic property is essentially relative, implying something distinguishable from, yet correlating with, itself. May we generalise the proposition, and affirm, That all properties are relative, and that every thing in nature has its characteristic property with reference, not to itself, but to something else? Or is this true only of some things and not of all — so that cognition may be something in the latter category?
This is an embarrassing question, which I do not feel qualified to decide: neither the general question, whether there be any cases of characteristic properties having no reference to any thing beyond themselves, and therefore not relative, but absolute — nor the particular question, whether cognition be one of those cases, implying no separate cognitum, but being itself both relatum and correlatum — cognition of cognition.[18]
[18] Plato, Charm. 168-169. 169 A: μεγάλου δή τινος ἀνδρὸς δεῖ, ὅστις τοῦτο κατὰ πάντων ἱκανῶς διαιρήσεται, πότερον οὐδὲν τῶν ὄντων τὴν αὑτοῦ δύναμιν αὐτὸ πρὸς ἑαυτὸ πέφυκεν ἔχειν, ἀλλὰ πρὸς ἀλλὸ — ἢ τὰ μέν, τὰ δ’ οὔ· καὶ εἰ ἔστιν αὖ ἅτινα αὐτὰ πρὸς ἑαυτὰ ἔχει, ἆρ’ ἐν τούτοις ἐστὶν ἐπιστήμη, ἣν δὴ ἡμεῖς σωφροσύνην φαμὲν εἶναι. ἐγὼ μὲν οὐ πιστεύω ἐμαυτῷ ἱκανὸς εἶναι ταῦτα διελέσθαι.