Science has not merely a theoretic value, its aim and purpose consist in its application to practical life. Science is throughout ethical. Thus ethics has also its mythological phase. In agreement with Professor Mach (p. 204), we should find it ridiculous if one who presumes to be an ethical teacher of mankind would say: “Man _must_ not be descended from monkeys,” “The earth _shall_ not rotate,” “Matter _ought_ not everywhere to fill space,” “Energy _must_ be constant,” and so on. Why is it ridiculous? Because we cannot prescribe a certain deportment to facts. It is however not ridiculous to let a precise and carefully sifted knowledge of facts determine our own deportment. Science has to teach ethics. But here also we should distinguish between positive facts and mythology. Ethics based upon mere theories, upon our interpretations of nature which we add to facts, is mythological; positive ethics is simply that deportment which is suggested by a comprehension of the facts themselves. Mythological ethics may be quite correct, just as much so as the application of a mythological theory of science may be within certain limits reliable as a working hypothesis. But it is desirable to understand the nature of mythological ethics in order to distinguish between truth and fiction. When Professor Mach speaks of sensations as being the elements of the world and of things as being complexes of these elements he apparently does not use the word sensation in its usual sense. It has ceased to be an abstract term which represents one feature only of a process of nature and has become a symbol for an entire reality. And is not such a usage of terms as if they were not abstracts but the things themselves liable to lead to misconceptions? Professor Mach’s “elements,” it seems to me, are only elements, i. e. ultimate and unanalysable materials, if considered as terms of a psychological view of the world; they are not elements in the domains of other abstractions, such as are made by physiology or physics. Moreover, although this method eliminates the duality of soul and body, mind and matter, feeling and motion, it does not explain the problem. Professor Mach might answer that the problem as to the duality of mind and matter is a sham problem, just as much as the problem why do we see things upright when the retina picture of the eye shows the things inverted? But a problem is to him who has solved the problem always a sham problem. Every problem disappears as a problem as soon as it is solved. It is true that we see as little with the blind spot of the eye as with the skin of our back. The problem of the blind spot is not why do we not see with the blind spot, (which is simply a matter of fact,) but why do we not notice, when using only one eye, its lack of sight in a spot surrounded with sight-seeing structures? We have to employ artificial means to convince ourselves that we are really blind in that spot!