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Returning to the senses we may briefly consider two questions—first their relation to the mind, secondly, their relation to outward objects:—

1. The senses are not merely 'holes set in a wooden horse' (Theaet.), but instruments of the mind with which they are organically connected. There is no use of them without some use of words—some natural or latent logic—some previous experience or observation. Sensation, like all other mental processes, is complex and relative, though apparently simple. The senses mutually confirm and support one another; it is hard to say how much our impressions of hearing may be affected by those of sight, or how far our impressions of sight may be corrected by the touch, especially in infancy. The confirmation of them by one another cannot of course be given by any one of them. Many intuitions which are inseparable from the act of sense are really the result of complicated reasonings. The most cursory glance at objects enables the experienced eye to judge approximately of their relations and distance, although nothing is impressed upon the retina except colour, including gradations of light and shade. From these delicate and almost imperceptible differences we seem chiefly to derive our ideas of distance and position. By comparison of what is near with what is distant we learn that the tree, house, river, etc. which are a long way off are objects of a like nature with those which are seen by us in our immediate neighbourhood, although the actual impression made on the eye is very different in one case and in the other. This is a language of 'large and small letters' (Republic), slightly differing in form and exquisitely graduated by distance, which we are learning all our life long, and which we attain in various degrees according to our powers of sight or observation. There is nor the consideration. The greater or less strain upon the nerves of the eye or ear is communicated to the mind and silently informs the judgment. We have also the use not of one eye only, but of two, which give us a wider range, and help us to discern, by the greater or less acuteness of the angle which the rays of sight form, the distance of an object and its relation to other objects. But we are already passing beyond the limits of our actual knowledge on a subject which has given rise to many conjectures. More important than the addition of another conjecture is the observation, whether in the case of sight or of any other sense, of the great complexity of the causes and the great simplicity of the effect.

The sympathy of the mind and the ear is no less striking than the sympathy of the mind and the eye. Do we not seem to perceive instinctively and as an act of sense the differences of articulate speech and of musical notes? Yet how small a part of speech or of music is produced by the impression of the ear compared with that which is furnished by the mind!

Again: the more refined faculty of sense, as in animals so also in man, seems often to be transmitted by inheritance. Neither must we forget that in the use of the senses, as in his whole nature, man is a social being, who is always being educated by language, habit, and the teaching of other men as well as by his own observation. He knows distance because he is taught it by a more experienced judgment than his own; he distinguishes sounds because he is told to remark them by a person of a more discerning ear. And as we inherit from our parents or other ancestors peculiar powers of sense or feeling, so we improve and strengthen them, not only by regular teaching, but also by sympathy and communion with other persons.

2. The second question, namely, that concerning the relation of the mind to external objects, is really a trifling one, though it has been made the subject of a famous philosophy. We may if we like, with Berkeley, resolve objects of sense into sensations; but the change is one of name only, and nothing is gained and something is lost by such a resolution or confusion of them. For we have not really made a single step towards idealism, and any arbitrary inversion of our ordinary modes of speech is disturbing to the mind. The youthful metaphysician is delighted at his marvellous discovery that nothing is, and that what we see or feel is our sensation only: for a day or two the world has a new interest to him; he alone knows the secret which has been communicated to him by the philosopher, that mind is all—when in fact he is going out of his mind in the first intoxication of a great thought. But he soon finds that all things remain as they were—the laws of motion, the properties of matter, the qualities of substances. After having inflicted his theories on any one who is willing to receive them 'first on his father and mother, secondly on some other patient listener, thirdly on his dog,' he finds that he only differs from the rest of mankind in the use of a word. He had once hoped that by getting rid of the solidity of matter he might open a passage to worlds beyond. He liked to think of the world as the representation of the divine nature, and delighted to imagine angels and spirits wandering through space, present in the room in which he is sitting without coming through the door, nowhere and everywhere at the same instant. At length he finds that he has been the victim of his own fancies; he has neither more nor less evidence of the supernatural than he had before. He himself has become unsettled, but the laws of the world remain fixed as at the beginning. He has discovered that his appeal to the fallibility of sense was really an illusion. For whatever uncertainty there may be in the appearances of nature, arises only out of the imperfection or variation of the human senses, or possibly from the deficiency of certain branches of knowledge; when science is able to apply her tests, the uncertainty is at an end. We are apt sometimes to think that moral and metaphysical philosophy are lowered by the influence which is exercised over them by physical science. But any interpretation of nature by physical science is far in advance of such idealism. The philosophy of Berkeley, while giving unbounded license to the imagination, is still grovelling on the level of sense.

We may, if we please, carry this scepticism a step further, and deny, not only objects of sense, but the continuity of our sensations themselves. We may say with Protagoras and Hume that what is appears, and that what appears appears only to individuals, and to the same individual only at one instant. But then, as Plato asks,—and we must repeat the question,—What becomes of the mind? Experience tells us by a thousand proofs that our sensations of colour, taste, and the like, are the same as they were an instant ago—that the act which we are performing one minute is continued by us in the next—and also supplies abundant proof that the perceptions of other men are, speaking generally, the same or nearly the same with our own. After having slowly and laboriously in the course of ages gained a conception of a whole and parts, of the constitution of the mind, of the relation of man to God and nature, imperfect indeed, but the best we can, we are asked to return again to the 'beggarly elements' of ancient scepticism, and acknowledge only atoms and sensations devoid of life or unity. Why should we not go a step further still and doubt the existence of the senses of all things? We are but 'such stuff as dreams are made of;' for we have left ourselves no instruments of thought by which we can distinguish man from the animals, or conceive of the existence even of a mollusc. And observe, this extreme scepticism has been allowed to spring up among us, not, like the ancient scepticism, in an age when nature and language really seemed to be full of illusions, but in the eighteenth and nineteenth centuries, when men walk in the daylight of inductive science.