The idea of duty, that recognition of something to be lived for beyond the mere satisfaction of self, is to the moral life what the addition of a great central ganglion is to animal life. No man can begin to mould himself on a faith or an idea without rising to a higher order of experience: a principle of subordination, of self-mastery, has been introduced into his nature; he is no longer a mere bundle of impressions, desires, and impulses.