THE KILL-JOY IN SCIENCE.--Philosophy separated from science when it asked the question, "Which is the knowledge of the world and of life which enables man to live most happily?" This happened in the Socratic schools; the veins of scientific investigation were bound up by the point of view of _happiness,_--and are so still. 8. PNEUMATIC EXPLANATION OF NATURE.--Metaphysics explains the writing of Nature, so to speak, _pneumatically,_ as the Church and her learned men formerly did with the Bible. A great deal of understanding is required to apply to Nature the same method of strict interpretation as the philologists have now established for all books with the intention of clearly understanding what the text means, but not suspecting a _double_ sense or even taking it for granted. Just, however, as with regard to books, the bad art of interpretation is by no means overcome, and in the most cultivated society one still constantly comes across the remains of allegorical and mystic interpretation, so it is also with regard to Nature, indeed it is even much worse. 9. THE METAPHYSICAL WORLD.--It is true that there _might_ be a metaphysical world; the absolute possibility of it is hardly to be disputed. We look at everything through the human head and cannot cut this head off; while the question remains, What would be left of the world if it had been cut off? This is a purely scientific problem, and one not very likely to trouble mankind; but everything which has hitherto made metaphysical suppositions _valuable, terrible, delightful_ for man, what has produced them, is passion, error, and self-deception; the very worst methods of knowledge, not the best, have taught belief therein. When these methods have been discovered as the foundation of all existing religions and metaphysics, they have been refuted. Then there still always remains that possibility; but there is nothing to be done with it, much less is it possible to let happiness, salvation, and life depend on the spider-thread of such a possibility. For nothing could be said of the metaphysical world but that it would be a different condition, a condition inaccessible and incomprehensible to us; it would be a thing of negative qualities. Were the existence of such a world ever so well proved, the fact would nevertheless remain that it would be precisely the most irrelevant of all forms of knowledge: more irrelevant than the knowledge of the chemical analysis of water to the sailor in danger in a storm. 10.