From these quotations it seems fairly sure that if we should ask Mr. Morgan, who is our best comparative psychologist, what took place in the mind of one of these cats of our experiments during the performance of one of the ‘tricks’ he would reply: “The cat performs the act because of the association of ideas. He is reminded by the sight of the box and loop of his experience of pulling that loop and of eating fish outside. So he goes and pulls it again.” This view has stood unchallenged, but its implication is false. It implies that an animal, whenever it thinks of an act, can supply an _impulse to do_ the act. It takes for granted that the performance of a cat who gets out of a box is mentally like that of a man who thinks of going down street or of writing a letter and then does it. The mental process is not alike in the two cases, for animals can _not_ provide the impulse to _do_ whatever act they think of. _No cat can form an association leading to an act unless there is included in the association an impulse of its own which leads to the act._ There is no general storehouse from which the impulse may be supplied after the association is formed. Before describing the experiments which justify these statements, it will be worth while to recall the somewhat obvious facts about the composition of one of these associations. There might be in an association, such as is formed after experience with one of our boxes, the following elements:— 1. Sense-impression of the interior of the box, etc. 2. (_a_) Discomfort and (_b_) desire to get out. 3. Representation of oneself pulling the loop. 4. Fiat comparable to the human “I’ll do it.” 5. The impulse which actually does it. 6. Sense-impression of oneself pulling the loop, seeing one’s paw in a certain place, feeling one’s body in a certain way, etc. 7. Sense-impression of going outside. 8. Sense-impression of eating, and the included pleasure. Also between 1 and 4 we may have 9, representations of one’s experience in going out, 10, of the taste of the food, etc. 6, 7 and 8 come after the act and do not influence it, of course, except in so far as they are the basis of the future 3’s, 9’s and 10’s. About 2 we are not at present disputing. Our question is as to whether 3 or 5 is the essential thing. In human associations 3 certainly often is, and the animals have been credited with the same kind. Whatever he _thinks_, Professor Morgan surely _talks_ as if 1 aroused 9 and 10 and 3 and leaves 5 to be supplied at will. We have affirmed that 5 is the essential thing, that no association without a specific 5 belonging to it and acquired by it can lead to an act. Let us look at the reasons.