Any one who has fully understood from the introductory essay the complete identity of the content of the principle of sufficient reason in all its different forms, must also be convinced of the importance of the knowledge of the simplest of these forms, as affording him insight into his own inmost nature. This simplest form of the principle we have found to be time. In it each instant is, only in so far as it has effaced the preceding one, its generator, to be itself in turn as quickly effaced. The past and the future (considered apart from the consequences of their content) are empty as a dream, and the present is only the indivisible and unenduring boundary between them. And in all the other forms of the principle of sufficient reason, we shall find the same emptiness, and shall see that not time only but also space, and the whole content of both of them, _i.e._, all that proceeds from causes and motives, has a merely relative existence, is only through and for another like to itself, _i.e._, not more enduring. The substance of this doctrine is old: it appears in Heraclitus when he laments the eternal flux of things; in Plato when he degrades the object to that which is ever becoming, but never being; in Spinoza as the doctrine of the mere accidents of the one substance which is and endures. Kant opposes what is thus known as the mere phenomenon to the thing in itself. Lastly, the ancient wisdom of the Indian philosophers declares, “It is Mâyâ, the veil of deception, which blinds the eyes of mortals, and makes them behold a world of which they cannot say either that it is or that it is not: for it is like a dream; it is like the sunshine on the sand which the traveller takes from afar for water, or the stray piece of rope he mistakes for a snake.” (These similes are repeated in innumerable passages of the Vedas and the Puranas.) But what all these mean, and that of which they all speak, is nothing more than what we have just considered—the world as idea subject to the principle of sufficient reason.