Behavior: An Introduction to Comparative Psychology

Watson argues that comparative psychology must abandon the anecdotal method and the inference of animal minds, and instead study behavior objectively as the relation between stimuli and responses. He rejects the introspective and anecdotal traditions that had dominated comparative psychology, including the collection of stories about clever animals and the attribution of human-like reasoning and emotion to them. The book proposes that psychology is a branch of natural science whose subject matter is the adjustment of organisms to environments, and it treats habits, instincts, and emotions as behavioral phenomena accessible to observation and experiment. Watson insists that animal behavior be described in terms of observable movements and the conditions that evoke them, not in terms of inferred mental states.

Both Watson and Thorndike rejected anecdotal methods and sought objective laws of animal learning, but their emphases differed. Thorndike's law of effect gave central place to the satisfying or discomforting after-effects of responses as the mechanism that strengthens or weakens stimulus-response bonds. Watson, while acknowledging the importance of consequences, was less interested in the mechanism of reinforcement and more interested in the stimulus-response connection as the unit of behavioral analysis. He sought to describe behavior in terms of the stimuli that elicit it and the responses that follow, treating habit formation as the acquisition of new stimulus-response connections. Watson's approach was more radical in its rejection of mentalistic explanation, while Thorndike retained a place for mental events and for the law of effect as a psychological principle.

In Behavior (1914), Watson treats instinct as a real category of behavior: complex, unlearned responses that are characteristic of a species and that appear without prior training. He discusses instinctive behavior in animals and humans and argues that instincts provide the raw material on which habit formation operates. This position changed dramatically in his later work. By the 1920s, Watson had largely abandoned the concept of instinct, arguing in Behaviorism (1924/1930) that most of what had been called instinct is actually the result of early training and conditioning. His famous claim that he could train any healthy infant to become any type of specialist reflected this environmentalist turn. The shift from instinct to environment as the primary explanatory principle is one of the most significant developments in Watson's career.

The book was widely reviewed and established Watson as a leading figure in American psychology. It was recognized as the first systematic statement of behaviorism as a research program in comparative psychology, and it influenced a generation of researchers in animal learning. The book's methodological prescriptions—objective observation, controlled experiment, rejection of anecdote—were broadly adopted even by psychologists who did not accept the more radical claims of Watson's later work. It also provoked criticism from those who argued that behaviorism could not account for the complexity of animal cognition or for the role of subjective experience in human psychology. The book's long-term significance is that it set the agenda for behaviorist research and provided the foundation for Watson's more comprehensive statement in Psychology from the Standpoint of a Behaviorist (1919).

Watson argues that psychology should be a natural science in the same sense as physics, chemistry, and biology: it should study observable phenomena, formulate laws, and aim at prediction and control. Its subject matter is behavior—what organisms do—and its data are the relations between environmental stimuli and behavioral responses. The implications are far-reaching. Introspection is rejected as a method, consciousness is not a subject matter, and mentalistic terms are to be translated into behavioral descriptions or eliminated. Psychology becomes continuous with biology and physiology, though its level of analysis is behavioral rather than neural. Watson's conception of psychology as a natural science was central to the behaviorist program and influenced later theorists who sought to make psychology objective, including Hull and Skinner, even as they disagreed about method and theory.

Behavior (1914) was Watson's first programmatic statement, addressed primarily to comparative psychologists. It was followed by Psychology from the Standpoint of a Behaviorist (1919), a systematic textbook for human psychology, and by Behaviorism (1924/1930), a popular presentation aimed at a general audience. The trajectory is one of increasing scope and public visibility: from animal research to human psychology to social applications. Watson's influence peaked in the 1920s, when behaviorism became the dominant orientation in American psychology. His later career was affected by personal scandal—a divorce that cost him his academic position—and he spent his later years in advertising, where he applied behavioral principles to marketing. The book's influence persisted through the work of later behaviorists, though Watson's specific formulations were revised and in some cases abandoned.