Generally considered to be a special case of Ockham’s razor in its application to animal or comparative psychology made by C. Lloyd Morgan (1852-1936) in his Introduction to comparative psychology (1894). Prior to Morgan, Wilhelm Wundt (1832-1920) put forward a similar idea in his Lectures on human and animal psychology (1863). The canon is summarised in the Introduction with the well-known sentence 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 exercise of one which stands lower in the psychological scale” (p. 53). Given this description, it is surprising that the canon was assumed to be a justification for the anti-mentalism of behaviourism during its dominant years in psychology. As Robert H. Wozniak, and others, have pointed out, this assumption was misplaced. In effect, Morgan’s canon does not amount to a principle of parsimony as it does not eradicate mental processes or hold that the only focus of study should be observable behaviour. Rather, it is an appeal to psychologists that they should know their own minds if they are to understand the conscious experience of other animals. Thus, it is not a denial of mental events in animals in the name of parsimony, but instead the opposite. More to the point, it was intended as a guide to psychologists as to how to use their own introspections in studying animal behavior within the broader context of a concern for mental evolution. In this respect, the canon emphasised the avoidance of imposing ‘higher’ mental functions on interpretations of animal behavior when ‘lower’ ones would suffice.
See Akaike’s information criterion, Comparative method, Ockham’s (or Occam’s) razor, Operationalism