Not nature, but science is to those idealist philosophers the source of truth. The "true idea" surpassed everything with them. This "idea" is forced by Hegel to roll about, and wind, and twist as if it were not a natural child, but a metaphysical dragon. But we cannot deny that in these twistings and windings of the Hegelian dragon the condition of the mind is exposed in all its peculiarities and nakedness. According to Hegel's theosophical opinion I do not become aware of my friend in material intercourse and bodily touch. Hegel's mark of a true friend is not that he proves true in life, but that he corresponds "to his idea." The "idea" of true friendship is for the idealist the measure of friendly truth, just as Plato measures the ideal or true condition of states and cooking pots of this valley of sorrows by the standard of an "idea" of the state, or an "idea" of the cooking pot, supposed to be derived from some other world. It is surely a valuable gift of nature that the human mind can form its ideals. But it is a gift that has also caused much trouble and which requires for its higher development the clear understanding that ideals are constructed out of real materials. Without this understanding the human race will never succeed in making a reasonable use of its ideal faculty. The beautiful ideal of true friendship may stimulate us to emulation. But the knowledge that it is nothing but an ideal which in reality is always mixed with a little falseness serves as no mean antidote against sentimental transcendentalism. And the same holds true of truth, liberty, justice, equality, brotherhood, etc. The striving after an ideal is very good, but it does no harm to be conscious of the fact and clearly see that any ideal can never be realized without some admixture of its opposite. What is it that Lessing says? "If God were to offer me the search for truth in his left hand, and truth in his right, I should grasp his left hand and say: Father, keep truth, it is for you alone." It has not been the task of philosophy to give us a true mind picture of the world. This it cannot do, this cannot be done by any scientific specialty. It may be done by the totality of sciences, and even by them only approximately. Even with them striving is a higher truth and of higher value than knowing. I repeat, then: It is not the particular task of philosophy to furnish a true picture of the world, but rather to investigate the method by which the human mind arrives at its world pictures. That is its work, and it is the object of this book to sketch its outline.