It is not till adolescence is reached that the mind grows able to take in the more abstract aspects of experience, the hidden similarities and distinctions between things, and especially their causal sequences. Rational knowledge of such things as mathematics, mechanics, chemistry, and biology, is now possible; and the acquisition of conceptions of this order form the next phase of education. Later still, not till adolescence is well advanced, does the mind awaken to a systematic interest in abstract human relations--moral relations, properly so called,--to sociological ideas and to metaphysical abstractions. This general order of sequence is followed traditionally of course in the schoolroom. It is foreign to my purpose to do more than indicate that general psychological principle of the successive order of awakening of the faculties on which the whole thing rests. I have spoken of it already, apropos of the transitoriness of instincts. Just as many a youth has to go permanently without an adequate stock of conceptions of a certain order, because experiences of that order were not yielded at the time when new curiosity was most acute, so it will conversely happen that many another youth is spoiled for a certain subject of study (although he would have enjoyed it well if led into it at a later age) through having had it thrust upon him so prematurely that disgust was created, and the bloom quite taken off from future trials. I think I have seen college students unfitted forever for 'philosophy' from having taken that study up a year too soon.