In idealism, as long as it remains within proper bounds, there is certainly truth; he who derides it, derides himself. But realism has also its truth, as long as it does not misjudge the worth of concepts, by which alone we clearly recognize what things are to us, what their relations to us are, and so how we have to deal with them. Concrete concepts inform us as to what is true and what is not true in phenomena. There is no greater mistake than to suppose that what things are in themselves, not what they are for us, is of importance to us; as if we could have an interest in that which things are not for us. The decisive point is the fact that, not things as they appear to us, but their rightly conceived appearance, their appearance as understood by adequate concepts, is the beginning and end of knowledge. Hence the true student of nature can no more do without the concept than the true philosopher can leave material perception out of account. Stiff-necked Materialism is as one-sided as old-time Metaphysics; the one has no meaning for its form, the other no form for its content; the one is a corpse, the other a ghost, and each strives in vain to attain the warmth of life. Natural Science and Philosophy must tread different paths, in so far as division of labor requires them to do so; but they labor at the two sides of one whole. Nature is not a machine, but life in its fullest form, and the task set us is to understand her as she is, not to patch together a nature out of disconnected scraps.