That truth upon matters small and contemptible deserves to be sought out and proved as much as upon matters great and sublime, is a doctrine affirmed in the Sophistês, Politikus, Parmenidês: Sophist. pp. 218 E, 227 A; Politik. 266 D; Parmenid. 130 E.
Thus far we are in dialectic: logical exposition proceeding by way of classifying and declassifying: in which it is assumed that the expositor will find minds unoccupied and unprejudiced, ready to welcome the truth when he lays it before them. But there are many topics on which men’s minds are, in the common and natural course of things, both pre-occupied and dissentient with each other. This is especially the case with Justice, Goodness, the Honourable, &c.[101] It is one of the first requisites for the expositor to be able to discriminate this class of topics, where error and discordance grow up naturally among those whom he addresses. It is here that men are liable to be deceived, and require to be undeceived — contradict each other, and argue on opposite sides: such disputes belong to the province of Rhetoric.
[101] Plato, Phædrus, p. 263 A.
The Rhetor does not teach, but persuades persons with minds pre-occupied — guiding them methodically from error to truth.
The Rhetor is one who does not teach (according to the logical process previously described), but persuades; guiding the mind by discourse to or from various opinions or sentiments.[102] Now if this is to be done by art and methodically — that is, upon principle or system explicable and defensible — it pre-supposes (according to Plato) a knowledge of truth, and can only be performed by the logical expositor. For when men are deceived, it is only because they mistake what is like truth for truth itself: when they are undeceived, it is because they are made to perceive that what they believe to be truth is only an apparent likeness thereof. Such resemblances are strong or faint, differing by many gradations. Now no one can detect, or bring into account, or compare, these shades of resemblance, except he who knows the truth to which they all ultimately refer. It is through the slight differences that deception is operated. To deceive a man, you must carry him gradually away from the truth by transitional stages, each resembling that which immediately precedes, though the last in the series will hardly at all resemble the first: to undeceive him (or to avoid being deceived yourself), you must conduct him back by the counter-process from error to truth, by a series of transitional resemblances tending in that direction. You cannot do this like an artist (on system and by pre-determination), unless you know what the truth is.[103] By anyone who does not know, the process will be performed without art, or at haphazard.
[102] Plato, Phædrus, p. 261 A. ἡ ῥητορικὴ τέχνη ψυχαγωγία τις διὰ λόγων, &c.
[103] Plato, Phædrus, pp. 262 A-D, 273 D.
He must then classify the minds to be persuaded, and the means of persuasion or varieties of discourse. He must know how to fit on the one to the other in each particular case.
The Rhetor — being assumed as already knowing the truth — if he wishes to make persuasion an art, must proceed in the following manner:— He must distribute the multiplicity of individual minds into distinct classes, each marked by its characteristic features of differences, emotional and intellectual. He must also distribute the manifold modes of discourse into distinct classes, each marked in like manner. Each of these modes of discourse is well adapted to persuade some classes of mind — badly adapted to persuade other classes: for such adaptation or non-adaptation there exists a rational necessity,[104] which the Rhetor must examine and ascertain, informing himself which modes of discourse are adapted to each different class of mind. Having mastered this general question, he must, whenever he is about to speak, be able to distinguish, by rapid perception,[105] to which class of minds the hearer or hearers whom he is addressing belong: and accordingly, which mode of discourse is adapted to their particular case. Moreover, he must also seize, in the case before him, the seasonable moment and the appropriate limit, for the use of each mode of discourse. Unless the Rhetor is capable of fulfilling all these exigencies, without failing in any one point, his Rhetoric is not entitled to be called an Art. He requires, in order to be an artist in persuading the mind, as great an assemblage of varied capacities as Hippokrates declares to be necessary for a physician, the artist for curing or preserving the body.[106]
[104] Plato, Phædrus, pp. 270 E, 271 A-D. Τρίτον δὲ δὴ διαταξάμενος τὰ λόγων τε καὶ ψυχῆς γένη, καὶ τὰ τούτων παθήματα, δίεισι τὰς αἰτίας, προσαρμόττων ἕκαστον ἑκάστῳ, καὶ διδάσκων οἵα οὖσα ὑφ’ οἵων λόγων δι’ ἣν αἰτίαν ἐξ ἀνάγκης ἡ μὲν πείθεται, ἡ δὲ ἀπειθεῖ.