Two passages seem to require more particular explanations. First, that which relates to the analysis of vision. The difficulty in this passage may be explained, like many others, from differences in the modes of conception prevailing among ancient and modern thinkers. To us, the perceptions of sense are inseparable from the act of the mind which accompanies them. The consciousness of form, colour, distance, is indistinguishable from the simple sensation, which is the medium of them. Whereas to Plato sense is the Heraclitean flux of sense, not the vision of objects in the order in which they actually present themselves to the experienced sight, but as they may be imagined to appear confused and blurred to the half-awakened eye of the infant. The first action of the mind is aroused by the attempt to set in order this chaos, and the reason is required to frame distinct conceptions under which the confused impressions of sense may be arranged. Hence arises the question, 'What is great, what is small?' and thus begins the distinction of the visible and the intelligible.
The second difficulty relates to Plato's conception of harmonics. Three classes of harmonists are distinguished by him:—first, the Pythagoreans, whom he proposes to consult as in the previous discussion on music he was to consult Damon—they are acknowledged to be masters in the art, but are altogether deficient in the knowledge of its higher import and relation to the good; secondly, the mere empirics, whom Glaucon appears to confuse with them, and whom both he and Socrates ludicrously describe as experimenting by mere auscultation on the intervals of sounds. Both of these fall short in different degrees of the Platonic idea of harmony, which must be studied in a purely abstract way, first by the method of problems, and secondly as a part of universal knowledge in relation to the idea of good.
The allegory has a political as well as a philosophical meaning. The den or cave represents the narrow sphere of politics or law (compare the description of the philosopher and lawyer in the Theaetetus), and the light of the eternal ideas is supposed to exercise a disturbing influence on the minds of those who return to this lower world. In other words, their principles are too wide for practical application; they are looking far away into the past and future, when their business is with the present. The ideal is not easily reduced to the conditions of actual life, and may often be at variance with them. And at first, those who return are unable to compete with the inhabitants of the den in the measurement of the shadows, and are derided and persecuted by them; but after a while they see the things below in far truer proportions than those who have never ascended into the upper world. The difference between the politician turned into a philosopher and the philosopher turned into a politician, is symbolized by the two kinds of disordered eyesight, the one which is experienced by the captive who is transferred from darkness to day, the other, of the heavenly messenger who voluntarily for the good of his fellow-men descends into the den. In what way the brighter light is to dawn on the inhabitants of the lower world, or how the idea of good is to become the guiding principle of politics, is left unexplained by Plato. Like the nature and divisions of dialectic, of which Glaucon impatiently demands to be informed, perhaps he would have said that the explanation could not be given except to a disciple of the previous sciences. (Symposium.)
Many illustrations of this part of the Republic may be found in modern Politics and in daily life. For among ourselves, too, there have been two sorts of Politicians or Statesmen, whose eyesight has become disordered in two different ways. First, there have been great men who, in the language of Burke, 'have been too much given to general maxims,' who, like J.S. Mill or Burke himself, have been theorists or philosophers before they were politicians, or who, having been students of history, have allowed some great historical parallel, such as the English Revolution of 1688, or possibly Athenian democracy or Roman Imperialism, to be the medium through which they viewed contemporary events. Or perhaps the long projecting shadow of some existing institution may have darkened their vision. The Church of the future, the Commonwealth of the future, the Society of the future, have so absorbed their minds, that they are unable to see in their true proportions the Politics of to-day. They have been intoxicated with great ideas, such as liberty, or equality, or the greatest happiness of the greatest number, or the brotherhood of humanity, and they no longer care to consider how these ideas must be limited in practice or harmonized with the conditions of human life. They are full of light, but the light to them has become only a sort of luminous mist or blindness. Almost every one has known some enthusiastic half-educated person, who sees everything at false distances, and in erroneous proportions.
With this disorder of eyesight may be contrasted another—of those who see not far into the distance, but what is near only; who have been engaged all their lives in a trade or a profession; who are limited to a set or sect of their own. Men of this kind have no universal except their own interests or the interests of their class, no principle but the opinion of persons like themselves, no knowledge of affairs beyond what they pick up in the streets or at their club. Suppose them to be sent into a larger world, to undertake some higher calling, from being tradesmen to turn generals or politicians, from being schoolmasters to become philosophers:—or imagine them on a sudden to receive an inward light which reveals to them for the first time in their lives a higher idea of God and the existence of a spiritual world, by this sudden conversion or change is not their daily life likely to be upset; and on the other hand will not many of their old prejudices and narrownesses still adhere to them long after they have begun to take a more comprehensive view of human things? From familiar examples like these we may learn what Plato meant by the eyesight which is liable to two kinds of disorders.
Nor have we any difficulty in drawing a parallel between the young Athenian in the fifth century before Christ who became unsettled by new ideas, and the student of a modern University who has been the subject of a similar 'aufklarung.' We too observe that when young men begin to criticise customary beliefs, or to analyse the constitution of human nature, they are apt to lose hold of solid principle (Greek). They are like trees which have been frequently transplanted. The earth about them is loose, and they have no roots reaching far into the soil. They 'light upon every flower,' following their own wayward wills, or because the wind blows them. They catch opinions, as diseases are caught—when they are in the air. Borne hither and thither, 'they speedily fall into beliefs' the opposite of those in which they were brought up. They hardly retain the distinction of right and wrong; they seem to think one thing as good as another. They suppose themselves to be searching after truth when they are playing the game of 'follow my leader.' They fall in love 'at first sight' with paradoxes respecting morality, some fancy about art, some novelty or eccentricity in religion, and like lovers they are so absorbed for a time in their new notion that they can think of nothing else. The resolution of some philosophical or theological question seems to them more interesting and important than any substantial knowledge of literature or science or even than a good life. Like the youth in the Philebus, they are ready to discourse to any one about a new philosophy. They are generally the disciples of some eminent professor or sophist, whom they rather imitate than understand. They may be counted happy if in later years they retain some of the simple truths which they acquired in early education, and which they may, perhaps, find to be worth all the rest. Such is the picture which Plato draws and which we only reproduce, partly in his own words, of the dangers which beset youth in times of transition, when old opinions