In the psychological aspect of play Dr. Groos assigns perhaps the first place to pleasure in the possession of power, or, as Preyer phrases it, pleasure in being a cause. We must be careful, however, lest in using such expressions we seem to imply that animals--even quite young animals--are capable of entertaining ideas which belong to a much later stage of mental development. Speaking of “joy in ability or power,” Professor Groos says,[132] “This feeling is first a conscious presentation to ourselves of our personality as it is emphasized by play.... But it is more than this; it is also delight in the control we have over our bodies and over external objects. Experimentation in its simple as well as its more complicated forms is, apart from its effect on physical development, educative in that it helps in the formation of causal associations.... The young bear that plays in the water, the dog that tears a paper into scraps, the ape that delights in producing new and uncouth sounds, the sparrow that exercises its voice, the parrot that smashes his feeding trough--all experience the pleasure in energetic activity, which is, at the same time, joy in being able to accomplish something.” But those who agree with Dr. Stout, as I do without hesitation, in denying personality (save in a very embryonic condition) and the conception of causation to animals in the perceptual stage of mental evolution, though they may find in Dr. Groos’s contention a central core of truth, will be unable fully to accept his manner of presenting it. “Any single train of perceptual activity,”[133] says Dr. Stout, “has internal unity and continuity. But where conscious life is mainly perceptual, the several trains of activity are relatively isolated and disconnected with each other. They do not unite to form a continuous system, such as is implied in the conception of a person. We must deny personality to animals.” To this I would merely add that, even where perceptual continuity in animals reaches its maximum, it is not reflectively grasped as a whole, and the ideal construction of the personal ego is not conceived as antithetical to the impersonal world of objects. With what Dr. Stout says about causality I am in complete agreement. “We must notice,”[134] he urges, “the essential difference which separates the merely perceptual category from that of ideational and conceptual thought. The perceptual category is always purely and immediately practical in its operation. It is a constitutive form of thought only because it is a constitutive form of action. The question ‘Why?’ has no existence for the merely perceptual consciousness. It does not and cannot inquire how it is that a certain cause produces a certain effect. It does not and cannot endeavour to _explain_, to analyze conditions so as to present a cause as a _reason_. It does not compare different modes of procedure or different groups of circumstances, so as to contradistinguish the