Voluntarism can as little be called scientific as can Mysticism. For both assert that the conceptual interpretation of the world is inadequate. Both demand, in addition to a principle of being which is ideal, also a principle which is real. But as perception is our only means of apprehending these so-called real principles, the assertion of Mysticism and Voluntarism coincides with the view that we have two sources of knowledge, viz., thought and perception, the latter finding individual expression as will and feeling. Since the immediate experiences which flow from the one source cannot be directly absorbed into the thoughts which flow from the other, perception (immediate experience) and thought remain side by side, without any higher form of experience to mediate between them. Beside the conceptual principle to which we attain by means of knowledge, there is also a real principle which must be immediately experienced. In other words, Mysticism and Voluntarism are both forms of Naïve Realism, because they subscribe to the doctrine that the immediately perceived (experienced) is real. Compared with Naïve Realism in its primitive form, they are guilty of the yet further inconsistency of accepting one definite form of perception (feeling, respectively will) as the exclusive means of knowing reality. Yet they can do this only so long as they cling to the general principle that everything that is perceived is real. They ought, therefore, to attach an equal value to external perception for purposes of knowledge. Voluntarism turns into Metaphysical Realism, when it asserts the existence of will also in those spheres of reality in which will can no longer, as in the individual subject, be immediately experienced. It assumes hypothetically that a principle holds outside subjective experience, for the existence of which, nevertheless, subjective experience is the sole criterion. As a form of Metaphysical Realism, Voluntarism is open to the criticism developed in the preceding chapter, a criticism which makes it necessary to overcome the contradictory element in every form of Metaphysical Realism, and to recognise that the will is a universal world-process only in so far as it is ideally related to the rest of the world. ADDITION TO THE REVISED EDITION (1918).