THE subject discussed in this book is one of the most important of the problems of philosophy, and it is not difficult to understand that in its application to real life it is of a paramount practical nature, not only in the domains of ethics and religion, but also in our general attitude toward the world and in our every-day doings.The idea of "things-in-themselves" originates as a natural phase in the evolution of human thought, and its formulation is as necessary as it is for certain purposes beneficial. In denouncing the belief in things-in-themselves as a superstition, we must therefore warn the student not to overlook the truth that is contained in it. For though there are no things-in-themselves, there are things, and, though it is not less wrong to hypostasize our ideas than it is to personify them in mythological figures, we must not regard them as flatus vocis only, as empty words, or mere names. For after all, they denote features of actual life which are real. And the concept of things-in-themselves underlies many other problems, where it is frequently so disguised as to be quite unrecognizable. For this reason it is not wise to deal with the subject off-hand, but to treat it in its connection with kindred questions in the domains of epistemology and metaphysics so called. Nor is it sufficient to state the solution only; it is also desirable to illustrate its importance by contrasting it with the views of philosophers that hold different opinions and still cling more or less to the antiquated belief in things-in-themselves.Modern thought appears negative to the followers of the old schools, but it has its positive aspects, and these positive aspects should be made prominent. In doing so we shall not only be just to the old schools, but also establish the claim of modern thought to its due share of influence upon the events of the world.When we recognise the Unknown, and also the infinitude of possible progress, we need no longer cling to the superstitious belief in the Unknowable. Further, when we understand that imagination, this child of sentiment and thought, has wings and that for all her erratic flights in the realm of fancy she now and then alights on a lofty crag in the ethereal realms of moral or religious aspiration to find there an important truth, which our slow-paced but sure-footed reason cannot as easily reach, we need neither insist upon the insufficiency and baseness of reason, nor extol the reliability of prophetic visions which are expressions of our religious instinct. In appreciating one faculty, we need not cast a slur upon the other.The relation between the circumference and the diameter of the circle is quite definite and concrete, but if expressed of a numerical fraction its value can only be approximated, admitting of an infinite progress in accuracy. So the world is determinable and science is reliable in spite of the fact that her work can never be finished, and however much we progress and advance in the solution of life's problem, we can never reach the end. But this condition of things is not depressive to a healthy mind. On the contrary, it is an elevating idea that the source of knowledge will never run dry, and that the waters of life are inexhaustible.