This doctrine, as it will be readily understood, does not in any sense deny the reality of the world in the ordinary acceptation of the term; it maintains merely that every object is conditioned by its subject; or, to explain the theory less technically, it will be sufficient to reflect that for the world, or for anything else, to be an object, there must be some one as subject to think it; for instance, the dreamless sleep proves that the earth exists only to the thinking mind, and should all Nature be rocked in an eternal slumber, there could then be no question of an exterior world.

If it be asked in what this perception consists, which represents the exterior world, we find that it is limited to three fundamental concepts, that of time, space, and their concomitant causality; but inasmuch as time and space are the receptacle of every phenomenon, once their ideality is established, the ideality of the world is proven at the same moment, and with it the truth of the formula, "The world is my idea."

Now the ideality of time is established, according to Schopenhauer, by what is known in mechanics as the law of inertia. "For what," he asks in the "Parerga," "does this law teach? Simply, that time alone cannot produce any physical action, that alone and in itself it alters nothing either in the repose or movement of a body. Were it either accidentally or otherwise inherent in things themselves, it would follow that its duration or brevity would affect them in a certain measure. But it does nothing of the sort; time passes over all things without leaving the slightest trace, for they are acted upon only by the causes that unroll themselves in time, but in no sense by time itself. When, therefore, a body is withdrawn from chemical action, as the mammoth in the ice fields, the fly in amber, and the Egyptian antiquities in their closed necropoli, thousands of years may pass and leave them unaffected. Indeed," he adds elsewhere, "the living toads found in limestone lead to the conclusion that even animal life may be suspended for thousands of years, provided this suspension is begun in the dormant period and maintained by special circumstances."

The "London Times," 21st September, 1840, contains a notice to the effect that, at a lecture delivered by Mr. Pettigrew, at the Literary and Scientific Institute, the lecturer showed some grains of wheat which Sir G. Wilkenson had found in a grave at Thebes, where they must have lain for three thousand years. They were found in an hermetically sealed vase. Mr. Pettigrew had sowed twelve grains, and obtained a plant which grew five feet high, and the seeds of which were then quite ripe.

Many other instances are given of this absolute inactivity; for example, let a body once be put in motion, that motion is never arrested or diminished by any lapse of time; it would be never ending were it not for the reaction of physical causes. In the same manner a body in repose would remain so eternally did not physical causes put it in motion. It follows, therefore, that time is not a real existence, but only a condition of thought, or purely ideal.

In regard to the ideality of space, Schopenhauer says, "The clearest and most simple proof of the ideality of space is that we can never get it out of our thoughts, as we might anything else. We can fancy space as having no longer anything to fill it, we can imagine that everything within it has disappeared, we can represent it as being, between the fixed stars, an absolute void, but space itself we can never get rid of; whatever we do, however we turn, there it is in endless expansion. This fact certainly proves that space is a part of our intellect; or, in other words, that it is the woof of the tissue upon which the different objects of the exterior world apply themselves. As soon as I think of an object, space appears with it and accompanies every movement, every turn and détour of my thought, as faithfully as the spectacles on my nose accompany every movement, every turn and détour of my person, or just in the same manner as the shadow accompanies the body. If I notice that a thing accompanies me everywhere, and under all circumstances, I naturally conclude that it is in some way connected with me; as if, for instance, wherever I went I noticed a particular odor from which I could not escape. Space is precisely the same; whatever I think of, what ever I imagine, space comes first and yields its place to nothing. It must, therefore, be an integral part of my understanding, and its ideality in consequence must extend to everything that is thinkable."

Space and time being but the empty framework of phenomenal existence, something must fill them, and that something is causality, which, according to Schopenhauer, is synonymous with action and matter. Into these abstract regions, however, it is unnecessary to follow him any further. Suffice it to say that having shown in this way that one of the two zones of which the world is formed is but an effect of the perceptions, he passes therefrom to the world as it is.

Now there were many paths which might or might not have led him to the unravelment of the great secret which Kant gave up in despair, there were many ways which seemed to tend to a direct solution of the Sphinx's riddle, but the course which he chose, and which brought him nearer to the proper answer than any other system of which the world yet knows, may be fairly said to have been inspired by the spirit of truth, and as an inspiration given first to him of all men.

It was not mathematics that he selected to aid him in his search for the real, for whatever the subtleties of that science may be, it is still too superficial to contain an explorable depth. The natural sciences could aid him as little. Anatomy, botany, and zoölogy reveal, it is true, an infinite variety of forms, but these forms at best are but unrelated perceptions, a series of indecipherable hieroglyphics. Even etiology, when embracing the whole range of physical science, gives at most but the nomenclature, succession, and changes of inexplicable forces, without revealing anything of their inner nature. All these methods were smitten with the same defect,—they were all external, and offered not the essence of things, but only their image and description. To employ them, therefore, in a search for truth would, he said, be on a par with a man who, wandering about a castle looking vainly for the entrance, takes meanwhile a sketch of the façade. Such, however, he noted, is the method which all other philosophers have followed. He concluded, therefore, as man was not only a thinking being, to whom the world was merely an idea, but an individual riveted to the earth by a body whose affections were the starting-point of his intuitions, that reality would come to him, not from without, but from within. "For this body of man's is," he argued, "but an object among other objects; its movements and actions are unknown to the thinking being save as are the changes of the others, and they would be as incomprehensible to him as his own were not their signification revealed to him in another manner. He would see movements follow motives with the constancy of a natural law, and would as little understand the influence of the motive as the connection of any other effect with its cause. He could, if he chose, call it force, quality, or character, but that is all that he would know about it."

What, then, is the interior essence of every manifestation and of every action? What is that which is identical with the body to such an extent that to its command a movement always answers? What is that with which Nature plays, which works dumbly in the rock, slumbers in the plant, and awakes in man? Schopenhauer answers with a word, "Will." Will, he teaches, is a force, and should not be taken, as it is ordinarily, to mean simply the conscious act of an intelligent being. In Nature it is a blind, unconscious power; in man it is the foundation of being.