“He who has received a benefit,” you say, “although he may have received it in the most generous spirit, has not yet fulfilled his whole duty, for the part of returning it still remains; just as in playing ball there is some merit in catching the ball with adroitness and accuracy, yet a man is not said to be a really good player unless he is clever and prompt in sending back the ball that he has received.” But your example is not well taken; and why? Because success in the game depends, not upon the mind of the player, but upon the motion and the agility of his body, and so an exhibition of which the eye is to be the judge must be shown in its entirety. Yet, for all that, I am not willing to say that a man who caught the ball as he ought was not a good player if, through no fault of his own, he was prevented from sending it back. “But,” you say, “although the player may not be lacking in skill since, while he did only half of his duty, the half that he did not do he is able to do, yet the placing itself remains imperfect, for its perfection lies in the interchange of throwing backwards and forwards.” I do not wish to refute the point further; let us agree to this, that, not the player, but the playing, lacks something; so also in this matter which we are now discussing, the object given lacks something, for another corresponding to it is still due, but the spirit of the gift lacks nothing, for it has discovered on the other side a corresponding spirit, and, so far as the purpose of the giver is concerned, it has accomplished all that it wished.