In boundless space countless shining spheres, about each of which, and illuminated by its light, there revolve a dozen or so of smaller ones, hot at the core and covered with a hard, cold crust, upon whose surface there have been generated from a mouldy film beings which live and know—this is what presents itself to us in experience as the truth, the real, the world. Yet for a thinking being it is a precarious position to stand upon one of those numberless spheres moving freely in boundless space without knowing whence or whither, and to be only one of innumerable similar beings who throng and press and toil, ceaselessly and quickly arising and passing away in time, which has no beginning and no end; moreover, nothing permanent but matter alone and the recurrence of the same varied organised forms, by means of certain ways and channels which are there once for all. All that empirical science can teach is only the more exact nature and law of these events. But now at last modern philosophy especially through Berkeley and Kant, has called to mind that all this is first of all merely a _phenomenon of the brain_, and is affected with such great, so many, and such different _subjective_ conditions that its supposed absolute reality vanishes away, and leaves room for an entirely different scheme of the world, which consists of what lies at the foundation of that phenomenon, _i.e._, what is related to it as the thing in itself is related to its mere manifestation. “The world is my idea” is, like the axioms of Euclid, a proposition which every one must recognise as true as soon as he understands it; although it is not a proposition which every one understands as soon as he hears it. To have brought this proposition to clear consciousness, and in it the problem of the relation of the ideal and the real, _i.e._, of the world in the head to the world outside the head, together with the problem of moral freedom, is the distinctive feature of modern philosophy. For it was only after men had spent their labour for thousands of years upon a mere philosophy of the object that they discovered that among the many things that make the world so obscure and doubtful the first and chiefest is this, that however immeasurable and massive it may be, its existence yet hangs by a single thread; and this is the actual consciousness in which it exists. This condition, to which the existence of the world is irrevocably subject, marks it, in spite of all _empirical_ reality, with the stamp of _ideality_, and therefore of mere _phenomenal appearance_. Thus on one side at least the world must be recognised as akin to dreams, and indeed to be classified along with them. For the same function of the brain which, during sleep, conjures up before us a completely objective, perceptible, and even palpable world must have just as large a share in the presentation of the objective world of waking life. Both worlds,