Modification by Experience 259 



latter require the inhibition of an entire instinct. The case 

 of the hermit crab, that of the chub presented with one pair 

 of forceps at a time, and that of the chub required to choose 

 between two differently colored forceps, may represent three 

 lessening degrees of the amount of inhibitory influence exerted 

 by experience. The hermit crab entirely abandoned its 

 ordinary method of reacting to light. The whole instinct 

 vanished. The chub, if it had refused as a result of expe- 

 rience to rise to the green fork when it was presented alone, 

 would have suspended an instinctive action so far as that 

 particular stimulus was concerned, and would have been 

 condemned to inactivity simply because no other stimulus 

 appealing to the nutritive instinct presented itself. The chub 

 offered a choice between two forks is not required to suspend 

 action at all, save for the brief interval necessary to discrimi- 

 nate between them. We should naturally expect that this 

 third state of affairs would be the easiest to bring about, and 

 such seems to be the case. It would probably be effected most 

 quickly when one of the stimuli was associated with positive 

 pain, instead of with mere absence of pleasure ; hence, very 

 likely, the extremely rapid learning of Morgan's chick. 

 Obviously the difference between the first and second of the 

 two cases just cited is at bottom one of degree, not of kind. 

 "A whole instinct" means, of course, a reaction to a whole 

 class of stimuli ; but the process by which light, for instance, 

 is discriminated from other forms of stimulation cannot be 

 ultimately different from the process by which one kind of 

 light stimulation is distinguished from another kind. 



As we survey the processes of learning involved in all these 

 methods, the labyrinth method, the puzzle-box method, the 

 method of inhibition, and the method of inhibition with choice, 

 we find that they are all cases of the checking of movements 

 which do not involve positively pleasurable results. Their 



