How far the gratification afforded by play is dependent on causality is strikingly shown by the fact that there is not a single form of it which does not exhibit in one shape or another the joy of being a cause as the germ of its attractiveness. It is true that this universal fact directs the attention more to the feeling of being a cause than to the logical idea of causal connection, yet we find enjoyment of logical activity prominent in the categories which we have designated as “hustling things about,” and as destructive and constructive movement play. The tendency toward such play was chosen for our point of departure, and the indications are that it is of the first importance to the child, and that only through frequent repetitions of the _post hoc_ does independent interest in the _propter hoc_ gradually arise. Still, it can not be denied that the true characteristics of play are in inverse ratio to the intensity of the desire for knowledge, and it should be clearly stated that we are now on the frontier territory of play and earnest. The steps by which we have reached this point can be clearly traced by every reader of what goes before; therefore, without stopping to recapitulate, I cite this striking remark of Preyer’s as a fitting climax. He says in reference to the evolution of a feeling of individuality: “Another important factor is the perception of change brought about by his own activity, in the familiar objects by which he is surrounded, and, psychologically speaking, or, indeed, from any standpoint, a red-letter day in the infant’s life is the one on which he first grasps the connection between his own movements and the sense-perceptions caused by them. The sound produced by tearing and crumpling paper was still unrecognised by this child till in his fifth month he discovered that it gave him a new sensation, and he repeated the experiment day after day most energetically until the stimulus of novelty wore away. Still, there was no clear apprehension of causality, but the child had now had the experience of being an originator, and of combined sight and sound perceptions, regular in so far that when he tore paper it became smaller for one thing, and sound resulted for another. Other such amusements were shaking keys on a ring, opening and shutting a box or purse (thirteen months), repeatedly filling and emptying a table drawer, piling up and scattering sand and gravel, rustling the pages of a book (thirteenth to nineteenth month), digging in sand, pulling footstools back and forth, laying stones, shells, and buttons in rows (twenty-one months), pouring water in and out of bottles, cups, and cans (thirty-first to thirty-third month) and throwing stones in water.”[333] Miss Shinn also gives a pretty example in the case of her little niece: “In the twentieth month (five hundred and ninetieth day) I saw her outdoors, especially when driving, cover her eyes several times with her hands. I thought the sunlight might be