In closing these remarks on movement-play we will notice briefly the distinction implied in our use of the word “sport,” since many of the games which we have been considering are so designated and practised by adults. What is it that converts play into sport? Preeminently the seriousness, the stress of earnestness with which it is pursued. Yet this statement is too general, for children too, as every one knows, are deeply earnest about their play, which does not on that account become a sport; and a man may play billiards or chess with such perseverance and zeal that his game becomes the principal event of his daily life, and yet he is not called a sportsman. We must evidently find a more specific definition. The fact that in the merest play all sorts of acts and achievements are involved which are not, as such, playful, but rather preparatory for play, may help us to this. In the eyes of adults the interest of a game lies in the construction of a theory for it; they busy themselves with perfection of form in play, with the rules of the game, with practice and training, with the proper outfit and suitable costume, etc. Only he who does so assiduously busy himself is a genuine sportsman, according to this theory. We may then define sport as play pursued reflectively, scientifically. This accounts for the fact that children are never sportsmen, despite the immense importance of their play to them, and that the mountain climber whose highest ideal is to conquer the heights, or the chess player who devotes all his spare time to the game, is still not a sportsman. III. PLAYFUL USE OF THE HIGHER MENTAL POWERS Rousseau, who dwells upon the fact that a man’s education begins at his birth, illustrates clearly, if somewhat exaggeratedly (being under the influence of Condillac), the threefold biological significance of youth when he says in the first volume of Émile that if man came into the world full grown he would be “un parfait imbécile, un automate, une statue immobile et presque insensible.” These words exactly fit into our subject and its classification. Having treated of the sensor and motor aspects of experimentation, we now proceed to examine its value to the higher mental life, where by its help man is rescued from the danger of remaining “un parfait imbécile.”