of energy which is seen to be nothing different from Kant's "principle of the persistence of substance." The concept of energy rests throughout on the category of Substantiality. Energy fulfils all the demands which the concept of substance in the philosophical sense involves. Substance in the philosophical sense is in modern physics not mass but energy. The theory of energy teaches that change takes place only when there is a difference of intensity of energy present, and that every form of energy strives to pass over from positions of greater intensity to positions of less intensity. This law of intensity is only the special form which the law of casuality takes on in the theory of energy. The categories of Substance and Cause do not suffice to determine the complex (Gefüge) of different forms of energy in the physical world. The real connection of things involves the further concept of System (Kant's community, reciprocity). Just as, in the categories of quantity, Unity and Plurality find their completion in Totality, and, in the qualitative categories, Ideality and Diversity come to a higher unity in Variability, so, in the categories of relation, System is the higher unity of reality in which Substantiality and Causality are contained as fundamentally constitutive. Thus the analysis of the modern concept of energy shows that the same categories are involved here that Kant derived from the forms of the judgment. The significance of the concept of energy for the theory of matter will be critically examined in a second paper.
On the nearest plane, the opposition between ego and world, subject and object, 'within me' and 'without me' is visual – spatial, and as such not to be resolved. But the epistemological problem is concerned only with the fact that the same experience is at once referred to the ego and localized without the ego. This apparent contradiction disappears when an experience is referred to the subject in so far as it is conceived to be dependent on one's body, to the object so far as it is found to depend on other objects in space. As every object of perception is determined in these two ways, there arise two closed series of relations, whose complete separation still remains only an ideal. A further separation of ego and non-ego occurs with the recognition of the body as itself an object of presentation. The class of experiences which are never objectified in the sense
