Scientists routinely employ metatheoretic principles, explicit discussion of which typically occurs in times of intense controversy, theoretical crisis, scientific revolution, and entry into a new domain. The writings of philosophers, including their disagreements, are often helpful in such circumstances. Whether knowledge of formal metatheory helps us in doing ''normal science'' is researchable. Much scientific thinking is of poor quality, and it could be improved by explicit metatheoretical education. Clinical practice and training programs should emphasize rational skepticism, respect for evidence, objectivity, and quantitative thinking. Because the relation between principles and success is probabilistic, metatheoretical research should implement the case study method by formal actuarial procedures.