The thought that Plato has expressed in this wonderful allegory has entered deeply into all philosophy. What we first take for reality is merely a shadow world. But in Plato's view it is the intellect which gives us the means of escape, the power to turn from the illusion to behold the reality. It is not until now that philosophy has sought the clue to the illusion in the nature of the intellect itself. The very instrument of truth is unfitted to reveal to us the reality as it is, because its nature and purpose is to transform reality, to make reality appear in a form which, though of paramount importance to us as active beings, is essentially an illusion. The intellectual bent of our mind leads us away from, and not towards a vision of reality in its purity. The more our intellect progresses, and the more and more clearly we see into a greater and ever greater number of things, the farther are we from, and not the nearer to a grasp of reality as it is. To obtain this vision of reality we have to turn away from the intellect and find ourselves again in that wider life out of which the intellect is formed. Life, as it lives, is an intuition that is nonintellectual.

"Human intelligence," writes Bergson, "is not at all what Plato taught in the allegory of the cave. Its function is not to look at passing shadows, nor yet to turn itself round and contemplate the glaring sun. It has something else to do. Harnessed, like yoked oxen, to a heavy task, we feel the play of our muscles and joints, the weight of the plough, and the resistance of the soil. To act and to know that we are acting, to come into touch with reality and even to live it, but only in the measure in which it concerns the work that is being accomplished and the furrow that is being ploughed, such is the function of human intelligence."

The illusion to which our intellectual nature subjects us is the necessity we are under to regard the things of the universe as more ultimate, as more fundamental than the movement which actuates the universe. It seems to us impossible that there could exist movement or change, unless there already existed things to be moved or changed, things whose nature is not altered, but only their form and their external relations, when they are moved or changed. This necessity of thought seems to have received authoritative recognition in all attempts, religious and scientific, to conceive origins. Thus we read in the Book of Genesis:

"In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters."

The matter of the universe, it is felt, must be in existence before the movement which vivifies it. The dead inert stuff must be created before it can receive the breath of life. And if God the creator is conceived as living before the matter which He has created, it is as an external principle, the relation of which to the creation is by most religious minds thought to transcend the power of the finite understanding to conceive.

The same fundamental conception of the primacy of matter over movement is evident in the scientific theories of the nature and origin of life. Life appears to science as a form of energy that requires things, matter occupying space, to support it. According to one view, life is the result of a certain combination or synthesis of chemical or physical elements, previously existing separately—a combination of very great complexity, and one that may possibly have occurred once only in the long process of nature, but which nevertheless might be, and some think probably, or even certainly, will be brought about by a chemist working in his laboratory. This is the mechanistic or materialist view. On the other hand, there is the theory of vitalism. Life, it is contended, cannot be due to such a synthesis of material elements as the mechanistic view supposes, because it is of the nature of an "entelechy"—that is, an individual existence which functions, as a whole, in every minutest part of the organism it "vitalises." Life has supervened upon, and not arisen out of the material organism which it guides and controls not by relating independent parts, but by making every part subserve the activity and unity of the whole. But the vitalist theory, as well as the mechanistic theory, conceives the movement and change which is life as dependent on the previous existence of a matter or stuff which is moved or changed. The philosophical conception differs, therefore, from both these theories. It is that life is an original movement, and that this movement is the whole reality of which things, inert matter, even spatial extension, are appearances. True duration is change, not the permanence of something amidst change. There are no unchanging things. Everything changes. Reality is the flux; things are views of the flux, arrests or contractions of the flowing that the intellect makes. The appearance of the world to us is our intellectual grasp of a reality that flows. This original movement is the life of the universe. Briefly stated, the argument on which the theory is based is that it is logically impossible to explain change by changelessness, movement by immobility. Real change cannot be a succession of states themselves fixed and changeless; real movement cannot be the immobile positions in which some thing is successively at rest. On the other hand, if movement is original, the interruption of movement, in whatever way effected, will appear as things. The experience which confirms this argument is the insight that everyone may obtain of the reality of his own life as continuous movement, unceasing change, wherein all that exists exists together in a present activity. To develop this argument would exceed the limits of this book, and would be outside its purpose. It is essential, however, that such a theory should be understood, for clearly it is possible to hold not only that we are subject to illusion, but that illusion is of the very nature of intellectual apprehension. If, then, the understanding works illusion for the sake of action, is it thereby disqualified as an instrument for the attainment of truth?

We are brought, then, to the critical point of our inquiry. If illusion is the essential condition of human activity, if the intellect, the very instrument of truth, is itself affected, what is to save us from universal scepticism? If the salt have lost his savour, wherewith shall it be salted? The intellect with its frames and moulds shapes living change and movement into fixed immobile states; the process of knowing alters profoundly the reality known. Must we not conclude that knowledge, however useful, is not true? And to what shall we turn for truth? There is, indeed, if this be so, a deeper irony in the question, What is truth? than even Pilate could have imagined. We have absolutely no practical concern with truth—we must leave it to the mystic, to the unpractical, the contemplative man who has turned aside from the stern task of busy life.

It is not so. The problem that seems so fundamental admits a quite simple solution. Illusion is not error, nor is it falsehood; it is the appearance of reality. It is the reality that appears, and when we grasp the principle of utility we understand the shape that the appearance must assume. This shape may seem to us a distortion, but in recognising appearance we are in touch with reality, and practical interest is the key that opens to us the interpretation of intellectual experience. And it is not only by the intellect that we interpret the nature of reality, for besides logic there is life, and in life we directly perceive the reality that in logic we think about.

The intellect, then, does not make truth, neither does it make reality; it makes reality take the form of spatial things, and it makes things seem to be the ground of reality. Were our nature not intellectual, if all consciousness was intuitive, the world would not then appear as things—there would be no things. But, notwithstanding that our world is an illusion, it is not the less on that account a true world, and our science is true knowledge, in the objective meaning of truth, for once an illusion is interpreted, it becomes an integral part of the conception of reality. It would be easy to find abundant illustration of this fact within science itself. Thus in the familiar case of the straight stick which appears bent when partly immersed in water, as soon as the illusion is understood as due to the different refraction of light in media of different density, air and water, it ceases to be an illusion. We then recognise that if a partly immersed stick did not appear bent, it would really be bent. Again, the illusion that clings to us most persistently throughout our experience is that which is connected with movement and rest. The system of movement in which we are ourselves carried along appears to us stationary, while that which is outside it seems alone to move. In very simple cases, such as viewing the landscape from a railway-carriage window, habit has long caused the illusion to cease, but we all remember the child's feeling that the trees and fields were flying past us. The earth's motion never becomes to us a real experience of movement, we accept the fact and never doubt the scientific evidence on which it rests, yet we always speak and think of sunrise and sunset; and this is not merely due to the accident that our language was fixed before the nature of the celestial movement was known, but to a natural illusion which it is far more convenient to retain than to abandon.

The fact of illusion is not the tenet of any particular philosophy, nor even of philosophy itself; it is a recognised factor in common life and in physical science, but in instancing the theory of Bergson's philosophy I am choosing an extreme case. Berkeley held that illusion is practically universal; Kant taught that the apparent objectivity of phenomena is the form that the understanding imposes on things; but Bergson teaches not only that all material reality is illusion, but also that this very illusion is the work of the intellect, that the intellect is formed for this purpose, intellect and matter being correlative, evolving pari passu. To such a doctrine there is of necessity a positive side, for it is impossible that it can rest on universal scepticism—scepticism both of knowledge and of the instrument of knowledge. If the intellectual view of reality as solid matter in absolute space is illusion, it must be possible to apprehend the reality from which the judgment that it is illusion is derived. If the intellect distorts, there must be an intuition which is pure, and the relation between these will be the relation between reality and appearance. Neither, then, is reality truth, nor appearance error. There is a truth of appearance, a truth that is a value in itself, a truth that is more than the mere negation that appearance is not reality. The appearance is our hold upon the reality, our actual contact with it, the mode and direction of our action upon it. What, then, is error? It cannot consist in the fact that we know appearance only, not reality, for we can only know reality by its appearance. It cannot be an appearance behind which there is no reality, for non-being cannot appear. It cannot be nothing at all or pure non-being, for to think of absolute nothing is not to think. In error there is some object of thought which is denied real being. What this is is the problem of error.