Difficulties and Methods 25 



of the corresponding process in the animal mind. For 

 example, we might say with a fair degree of assurance that 

 an animal consciously discriminates between light and 

 darkness; that is, receives conscious impressions of dif- 

 ferent quality from the two, yet the mental impression 

 produced by white light upon the animal may be very 

 different from the sensation of white as we know it, and 

 the impression produced by the absence of light very dif- 

 ferent from our sensation of black. Black and white may, 

 for all we know, depend for their quality upon some sub- 

 stance existing only in the human retina. 



A second precaution concerns the simplicity or complexity 

 of the interpretation put upon animal behavior. Lloyd 

 Morgan, in his " Introduction to Comparative Psychology," 

 formulated a conservative principle of interpretation which 

 has often been quoted as " Lloyd Morgan's Canon." The 

 principle is as follows : "In no case may we interpret an 

 action as the outcome of the exercise of a higher psychical 

 faculty, if it can be interpreted as the outcome of the exer- 

 cise of one which stands lower in the psychological scale" 

 (505, p. 53). In other words, when in doubt take the 

 simpler interpretation. For example, a dog detected in 

 a theft cowers and whines. One possible mental accom- 

 paniment of this behavior is remorse ; the dog is conscious 

 that he has fallen below a moral standard, and grieved' 

 or offended his master. A second is the anticipation of 

 punishment; the dog has a mental representation of the 

 consequences of his action upon former occasions, and 

 imagining himself likely to experience them anew, is terrified 

 at the prospect. A third possibility is that the dog's pre- 

 vious experience of punishment, instead of being revived in 

 the form of definite images, makes itself effective merely in 

 his feelings and behavior ; he is uncomfortable and fright- 



