The attempt to render morality scientific ends in a result fatal to morality; and the reason seems clear. It is that science is not morality, nor are the principles of science those of morality. Science is knowledge, morality is action. Knowledge, to be knowledge, has to presuppose that Nature is uniform and that the things it deals with are real. So, too, action, to be moral, requires the belief that our moral ideals are real and that we are free to choose between good and evil. The optimist who would have us believe that science includes all the remaining articles of the common faith, and the pessimist who argues that it excludes them, alike fall into the error of imagining that science, the knowledge of what is, is the whole of knowledge, and that the assumptions which are required in order to describe what is will enable us to do and to know what ought to be. Science, which is a true description of part of our experience, becomes a misleading half-truth when it is offered as an exhaustive account of the whole. If, knowing the rules of chess and having a record of the moves in a solitary (and unfinished) game, we refused to inquire why the pieces moved, on the ground that if we succeeded in the inquiry we should have made no addition to our knowledge of the way in which the pieces do move, we should never understand the game. But we should be nearer the truth than if we assumed that a piece caused its own movements or those of the other pieces; and that will or purpose was quite incompatible with the uniformity of their movements.