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.”
Paramecium does not change its response to, say, an obstacle in the water, from swimming backward, turning to one side and swimming forward by abbreviating and eventually omitting the turn and the backward movement. The schoolboy does not tend to count 1, 2, 10 or to say a, b, z, or give ablative plurals after nominative singulars.
Repetition of a series of physiological states in and of itself on the contrary makes an animal increasingly more likely to maintain the series in toto. It is hard to give the first and then the last word of an oft repeated passage like Hamlet’s soliloquy or the Lord’s Prayer, or to make readily the first and then the last movement of writing a name or address. Repetition never eliminates absolutely and eliminates relatively the less often or less emphatically connected.
Even if supplemented by the law of effect, so that some force is at hand to change the effect of S upon the animal to A D instead of the original A B C D, the law of the resolution of physiological states would be relevant to only a fraction of learning. For example, let a cat or dog be given an ordinary discrimination experiment, but so modified that whether the animal responds by the ‘right’ or the ‘wrong’ act he is removed immediately after the reward or punishment. That is, the event is either S R1 or S R2, never S R1 R2. Let the experiment be repeated at intervals so long that the physiological state, St. R1, or St. R2, leading to the response R1 or R2 in the last trial, has ceased before the next. The animal will come to respond to S by R2 only, though R2 has never been reached by the ‘resolution’ of S R1 R2.
Cats in jumping for birds or mice, men in playing billiards, tennis or golf, and many other animals in many other kinds of behavior, often learn as the dog must in this experiment. The situation on different occasions is followed by different responses, but by only one per occasion. Professor Jennings was misled by treating as general the special case where the situation itself includes a condition of discomfort terminable only by a ‘successful’ response or by the animal’s exhaustion or death.