This paper seeks to reappraise and describe, from primary sources, the methodological, ethical, and clinical implications of the experiment by John B. Watson and Rosalie Rayner, published a century ago (1920) in the Journal of Experimental Psychology. The experimental study is described in detail, including its background, description of the procedure, and the conclusions that Watson and Rayner initially reached. Then some later publications are presented in which Watson and Rayner raised postulates similarly to those of the 1920 experiment. Then, the way the study is presented in the psychological literature, typically with distortions, is discussed, along with the respective clarifications. The most common methodological and ethical criticisms of the experiment are reviewed subsequently. These historical presentism of the critics is questioned, because they does not consider that contemporary ethics committees that supervise research based on national and international regulations did not exist at that time. Finally, the study’s scientific and applied contributions are synthesized in terms of verifying the learned character of phobias and the initial approach to modification techniques, which are later formalized as behavior therapy.
