Although Thomas Aquinas never developed an account of the emotional disorders, he anticipated all the major principles and methods of cognitive therapy (CT) in his philosophical psychology. This fact has gone largely unnoted by philosophers and psychologists alike. The purpose of this article is to demonstrate the complementarity of these two psychologies by arguing that Aquinas’s philosophical psychology (APP) can serve as a theoretical framework for CT, especially as it appears in Aaron Beck’s classic introduction to the subject, Cognitive Therapy and the Emotional Disorders. The motivation for this article is both theoretical and practical in nature: Theoretical, because Aquinas provides a profound and cogent philosophical framework for CT, which in turn is able to draw out much that is only implicit in Aquinas’s thought; practical, because APP offers useful insights and suggests interesting lines of development for CT. Finally, I suggest that the disagreements dividing the various different psychologies and their related approaches to the emotional disorders may be due to a failure to grasp the dynamic structure of the human psyche at a level that can be reached only through careful philosophical analysis, a feat I believe Aquinas to have in large measure achieved.