Not such complete agreement, however, exists in regard to the question by what symbols of human thought and speech these laws can be described in part as well as _in toto_, so that existing laws can not only be _fully_ and conclusively defined, but at the same time without the use of _superfluous_ terms. According to _Ernst Mach_, thought is an adaptation to facts. Our speech is simply a method of expression of our thoughts and indeed the most satisfactory form we have. We must, therefore, use those symbols which are most closely adapted to facts as the most precise expression of these existing laws. What forms of expression have we? It might appear that a discussion of this fundamental question has not a close connection with our special subject of physiology of stimulation. This, however, is not the case. Indeed, it is an irremissibly previous requirement not only for the elucidation, but also for the understanding itself in this particular field. We _could not_ come to a clear understanding in this field without such analysis. The interpretation of the unity of being and happenings in accordance with natural laws, which today is widely accepted in the scientific world as the only exact one, implies the assumption of a “_causation_” according to which things are explained by the law of “_cause_” and “_effect_.” I[14] have already on various occasions taken the opportunity to criticise this view and to show the error and confusion to which it leads. I should like here to enter somewhat more in detail into the reason for this criticism. It is particularly directed against the scientific use of the term “_cause_” on the basis of our best-known theoretical principles. It is clear that all scientific observations and explanations are founded on experience. Can it be said that the conception of “cause” originates from experience? [14] Compare with this _Max Verworn_: “Die Entwickelung des menschlichen Geistes.” Jena, Gustav Fischer, 1910. _Max Verworn_: “Die Erforschung des Lebens.” II Auflage. Jena, _Gustav Fischer_, 1911. The same: “Die Fragen nach den Grenzen der Erkenntniss.” Jena, _Gustav Fischer_, 1908. The same: “Allgemeine Physiologie.” V Auflage. _Gustav Fischer_, 1909.