We need hardly again remind ourselves that this conception of worth, or of man as end _per se_, is not a mere abstraction, and that our interest in it is not academic. Every outcry against the oppression of man by man, or against whatsoever is morally hideous, is but the affirmation of the cardinal principle that a human being as such is not to be violated, is not to be handled like a tool, but is to be respected and revered as an end _per se_. But what do we mean by end _per se_, and how account for this notion? Does it come into our mind like a bolt from the blue, or is it revealed as prefigured in the human mind when we follow it into its intimate constitution? Our knowledge of the world we live in is extremely limited—in its details it is confined to the planet we live on, extending to the myriads of celestial bodies beyond us only by means of scant generalizations. If we have knowledge of only so small a portion, how can we frame an ideal of the whole? At the same time we must remember that the world we actually know, this earth and yonder starry myriads, is in very truth _our_ world, the world as it exists for us, a world which with the help of data coming to us from the unknown, we ourselves have built up on certain constructive principles; and that these principles have been found, within certain limits, availing.[27] I say availing within certain limits. The defeat they meet with beyond those limits is due to the intractable elements of juxtaposition and sequence, of the time and space manifolds, which in themselves are incapable of being completely rationalized. Now the ideal of the whole is a plan or scheme in which the constructive principles of the mind are conceived as having untrammeled course and unhindered application, and the task of world-building, or rather universe-building, is in idea carried out to completion.