But it is clear that man can and does reflect, not only on the way in which the mechanism acts, but also on the use to which he puts it and the relation of that use to his ideals. These reflections may add nothing to his science, to his knowledge that rooks when moved must be moved parallel to the sides of the board, but they do add to his knowledge of the game. In fine, man gains a more important part of that knowledge by or in playing the game than he does by studying the rules. The rules acquaint him with the resources which are at his disposal, the capacities of the various pieces and the powers of the various forces of Nature or human nature. But it would be absurd to pass this off as a complete knowledge of the game. We may, by playing the game, add only to our knowledge of how the game ought to be played, of how the mechanism of Nature and human nature ought to be used, and not add to our knowledge of the fact that if and when the mechanism is set agoing it acts in the way described by science. But the one kind of knowledge, though not science, is just as true as the other, on the same terms, viz. if you accept the assumptions presupposed by it. Science, then, is from the very terms of its constitution abstract, _i.e._ essentially incomplete. The very terms on which alone science is possible are that it shall study one aspect only of Nature, the mechanical, and shall ascertain what conclusions follow if we confine our attention to the mechanical factors and neglect certain other factors--the freedom of the will, final causes, and the moral and æsthetic ideals--which, though voluntarily neglected for the moment, are yet known to be important factors in the game of life as it is played by us. As often as we act, however, we set those factors, temporarily neglected by science, in action; and there is no reason why, when we have acted, we should not reflect upon our action, disengage the assumptions which are presupposed by our actions, and then reconsider the world and life in the light of the assumptions on which our actions and the actions of all men are based, viz. the freedom of the will and the reality of our ideals. Thus viewed, the world becomes the scene and life the opportunity of using the forces of Nature and our own psychological mechanism for the purpose of achieving the ideal.