C. Lloyd Morgan is widely credited as the “father of comparative psychology” due to his contribution of guidelines for the psychological interpretation of animal behavior. Many modern comparative psychologists believe that constraints encouraged by Morgan are now obsolete and some assert that adherence to the canon restricts further progress in the field. Nonetheless, Morgan’s guidance continues to be important in comparative psychology. A review of Morgan’s canon, its historical misuse, and consideration of popular alternatives reinforce Morgan’s role in comparative psychology. A recent model of cognitive evolution highlights the importance of Morgan’s guidelines and an illustration of the continued usefulness of the canon is given in the context of investigations of theory of mind in chimpanzees.