§ 8. As from the direct light of the sun to the borrowed light of the moon, we pass from the immediate idea of perception, which stands by itself and is its own warrant, to reflection, to the abstract, discursive concepts of the reason, which obtain their whole content from knowledge of perception, and in relation to it. As long as we continue simply to perceive, all is clear, firm, and certain. There are neither questions nor doubts nor errors; we desire to go no further, can go no further; we find rest in perceiving, and satisfaction in the present. Perception suffices for itself, and therefore what springs purely from it, and remains true to it, for example, a genuine work of art, can never be false, nor can it be discredited through the lapse of time, for it does not present an opinion but the thing itself. But with abstract knowledge, with reason, doubt and error appear in the theoretical, care and sorrow in the practical. In the idea of perception, illusion may at moments take the place of the real; but in the sphere of abstract thought, error may reign for a thousand years, impose its yoke upon whole nations, extend to the noblest impulses of humanity, and, by the help of its slaves and its dupes, may chain and fetter those whom it cannot deceive. It is the enemy against which the wisest men of all times have waged unequal war, and only what they have won from it has become the possession of mankind. Therefore it is well to draw attention to it at once, as we already tread the ground to which its province belongs. It has often been said that we ought to follow truth even although no utility can be seen in it, because it may have indirect utility which may appear when it is least expected; and I would add to this, that we ought to be just as anxious to discover and to root out all error even when no harm is anticipated from it, because its mischief may be very indirect, and may suddenly appear when we do not expect it, for all error has poison at its heart. If it is mind, if it is knowledge, that makes man the lord of creation, there can be no such thing as harmless error, still less venerable and holy error. And for the consolation of those who in any way and at any time may have devoted strength and life to the noble and hard battle against error, I cannot refrain from adding that, so long as truth is absent, error will have free play, as owls and bats in the night; but sooner would we expect to see the owls and the bats drive back the sun in the eastern heavens, than that any truth which has once been known and distinctly and fully expressed, can ever again be so utterly vanquished and overcome that the old error shall once more reign undisturbed over its wide kingdom. This is the power of truth; its conquest is slow and laborious, but if once the victory be gained it can never be wrested back again.