Abstract
Background: As Mariano Yela is one of the most eminent Spanish psychologists, the centenary of his birth is a good occasion to revisit his work. Despite being best known for his contributions to psychometrics, Yela has also made important contributions to theoretical psychology, with particular interest in the question of its unity-diversity. Method: Some of his most important theoretical works, presented in various contexts, were reviewed. Results: One conception of psychology and one concern are emphasized throughout his work. The conception of psychology is based on behavior as meaningful action. The concern is to see any possible unity in the diversity of psychology. Conclusions: The structure of behavior defined by subject, situation and action emerge as the basis on which the unity of psychology could be established. If anything, unity of diversity. Some implications are discussed.
