Coined by 19th-century British psychologist C. Lloyd Morgan, Morgan's Canon (sometimes called Lloyd Morgan's Canon or Morgan's Canon of Interpretation) remains a fundamental precept of comparative (animal) psychology. It states that:

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.

Morgan was reacting to excessively anthropomorphic interpretation of animal behavior, specifically the anecdotal approach of George Romanes. D.A. Dewsbury in Comparative psychology in the twentieth century calls Morgan's Canon "[p]erhaps, the most quoted statement in the history of comparative psychology", which Frans de Waal echoes in The Ape and the Sushi Master: "perhaps the most quoted statement in all of psychology".

In 1903, Morgan added a revised version of the Canon:

In no case is an animal activity to be interpreted in terms of higher psychological processes, if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development.

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Interpretation of Morgan's Canon is not without controversy; see:

(Morgan's original Canon appears at 53 Morgan, 1894; the revised canon at 59 Morgan, 1903.)