There has been one notable attempt to explain the facts of learning by an even simpler theory than that represented in the laws of exercise and effect. Jennings has formulated as an adequate account of learning the law that: “When a certain physiological state has been resolved, through the continued action of an external agent, or otherwise, into a second physiological state, this resolution becomes easier, so that in course of time it takes place quickly and spontaneously” (‘Behavior of the Lower Organisms,’ p. 289). “The law may be expressed briefly as follows:—_The resolution of one physiological state into another becomes easier and more rapid after it has taken place a number of times._ Hence the behavior primarily characteristic for the second state comes to follow immediately upon the first state. The operations of this law are, of course, seen on a vast scale in higher organisms in the phenomena which we commonly call memory, association, habit formation and learning” (_ibid._, p. 291). This law may be expressed conveniently as a tendency of a series of states A -> B -> C -> D to become A -> D or A -> B¹ -> C¹ -> D B¹ and C¹ being states B and C passed rapidly and in a modified way so that they do not result in a reaction but are resolved directly into D. If Professor Jennings had applied to this law the same rigorous analysis which he has so successfully employed elsewhere, he would have found that it could be potent to cause learning only if supplemented by the law of effect and then only for a fraction of learning. For, the situations being the same, the state A cannot produce, at one time, now B and, at another time, abbreviated, rudimentary B¹ instead of B. If A with S produces B once, it must always. If D or a rudimentary B¹ is produced, there must be something other than A; A must itself have changed. Something must have been added to or subtracted from it. In Professor Jennings’ own words, “Since the external conditions have not changed, the animal itself must have changed” (_ibid._, p. 286). And in adaptive learning something related to the results of the S A connection must have changed it. The series A—B—C—D does not become the series A—D or A—B¹—C¹—D by magic. If B and C are weakened and D is strengthened as sequents of A in response to S, it is because something other than repetition acts upon them. Repetition alone could not blow hot for D and cold for B. Moreover, as a mere matter of fact, “the resolution of one physiological state into another” through intermediate states does not with enough repetition “become easier so that in course of time it takes place quickly and spontaneously.”