I wish to observe here, however, that the conception of cause, even though more or less unconsciously so, is still the remains of a part of the old anthropomorphic mysticism carried over into our own times. This shows itself especially in the conception of _force_, which is nothing more than a form of the conception of cause. Force is the cause of movement. One has here in anthropomorphic manner transferred the action of the _will_ of man, which produces movement of the muscles, into lifeless nature. The force of the sun attracts the earth, that of the magnet attracts iron, etc. In short, one has introduced a mysterious unknown factor instead of being content with the simple description of facts, such as _Kirchhoff_[15] has advanced in the field of mechanics. Although of late natural science has also dispensed more and more with conception of force as a means of explanation, it is still today not wholly done away with. That which applies to the conception of force is likewise true of the conception of cause. [15] _Gustav Kirchhoff_: “Vorlesungen über mathematische Physik. Mechanik.” Leipzig 1876. Another point concerning the application of the conception of cause seems to me, however, to be of much more importance, namely that a single cause is held responsible for the taking place of a process. One endeavors to explain a process in general by seeking for its “cause.” The cause being found, the process is considered as fully accounted for. This idea is not only widely spread in everyday life, but is even found frequently in natural science, especially in biology, although here, it should be known, the processes are decidedly more complicated. The search for the “cause” of development, for the “cause” of heredity, for the “cause” of death, for the “cause” of the respiration, for the “cause” of the heart beat, for the “cause” of sleep, for the “cause” of disease, etc., was for a long time and frequently even today a characteristic of biological investigation. As if such a complicated process as development, death or disease could be explained by a single factor! In reality, one has obtained very little as a result of the analysis of a process by discovering its cause; and in addition the false impression arises that through the finding of this one factor the process has been definitely explained. It has been generally recognized in the natural sciences in recent times that no process in the world is dependent upon one single factor and attempts have been made to give this fact more consideration.