The question arises, What is experience? Experience presupposes a 'given,' which must be explained by reference to the ego. The difficulties of the 'given' rest entirely on the fact that the ego has usually been considered abstractly; certain fundamental feelings and logical functions are attributed to the ego, but the objects determined by them are not so attributed. The ego is the concrete whole composed by the relations and the given. Hence it follows that we are necessarily limited to experience and cannot seek explanations in unknown substances. The ego is not to be defined merely as the sum of conscious processes, as Ziehen defines it, or as a process among the others. There are no egoless processes. The fact that the pure ego is an abstraction does not mean that the ideal unity of consciousness can be ruled out of epistemology. Ziehen's question: Does the young child have an idea of the ego? has no bearing; for no one doubts that the individual ego has a beginning in time, and, even if the child has not separated the ego from the conscious processes, it does not follow that the unity of consciousness is inoperative. The fundamental fact for epistemology still remains, viz., that without the ego there can be no knowledge. Similarly, the fact that one is not always conscious of the ego does not disprove its existence; it exists in the particular ideas even if it is not consciously analyzed out of them. Hence the universal is always given in the particular, and either alone is an abstraction. This is not a doctrine of psychic activities, but an investigation of the facts of experience.
A physical science is one which employs in its description of nature only such terms as can adequately be defined by the use of the measuring rod. By description of nature is here meant the body of laws which a science has formulated. Such a law is physical, if it presupposes no knowledge except such as is involved in the use of the measuring rod. Thus defined, physical science includes the part of geometry which records the results of measurement. Mass, length, and time are amenable to the measuring rod, and hence mechanics is a physical science. All the units of general physics are ultimately determined in the same way. But there are sciences whose terms cannot be expressed by measurement. It seems absurd to seek a physical explanation of acts which we ordinarily explain from motives. The animal body may be explained by physical laws, but it is directed by a soul which apparently cannot be so explained. Is this inexplicability demonstrable? A law can be proved inadequate to the explanation of phenomena only on condition: (1) that the law and the phenomena are described in the same set of terms; (2) that the law is restricted in its application. Obviously, therefore, to say that human character cannot be explained mechanically is meaningless, for the law and the phenomena are in different terms. What, then, is a non-physical
