In its universal search from the attribute to the substance, from the relative to the absolute, from the appearance of things to the true things, the mind finally arrives at the understanding that the substance is nothing but a sum of attributes collected by brain activity, and that the mind itself, or reason, is a substantial being which creates abstract mental units out of a multitude of sense perceptions and conceives of the universe as an absolute whole, as an independent "thing itself," by adding all its transient manifestations. In turning away full of dissatisfaction from attributes, searching restlessly after the substance, throwing aside phenomena, and forever groping for truth, for the nature of things, for the "thing itself," and in finally realizing that this substantial truth is merely the sum of all socalled untruths, the totality of all phenomena, the mind proves itself to be the creator of the abstract concept of substance. But it did not create this concept out of nothing. On the contrary, it generated the concept of a world substance out of attributes, it derived truth out of manifestations of things. The idealist conception that there is an abstract nature behind phenomena which materialises itself in them, is refuted by the understanding that this hidden nature does not dwell in the world outside of the human mind, but in the brain of man. But since the brain differentiates between phenomena and their nature, between the concrete and the general, only by means of sense perception, it cannot be denied that the distinction between phenomena and their nature is well founded; only the essential nature of things is not found back of phenomena, but by means of phenomena. This nature is materially existent and our faculty of thought is a real and natural one.