The Essays of Arthur Schopenhauer; On Human Nature

Truths of the physical order may possess much external significance, but internal significance they have none. The latter is the privilege of intellectual and moral truths, which are concerned with the objectivation of the will in its highest stages, whereas physical truths are concerned with it in its lowest.

For example, if we could establish the truth of what up till now is only a conjecture, namely, that it is the action of the sun which produces thermoelectricity at the equator; that this produces terrestrial magnetism; and that this magnetism, again, is the cause of the aurora borealis, these would be truths externally of great, but internally of little, significance. On the other hand, examples of internal significance are furnished by all great and true philosophical systems; by the catastrophe of every good tragedy; nay, even by the observation of human conduct in the extreme manifestations of its morality and immorality, of its good and its evil character. For all these are expressions of that reality which takes outward shape as the world, and which, in the highest stages of its objectivation, proclaims its innermost nature.