Although it is generally acknowledged that the modern science of psychology was produced in the mid-nineteenth century by the cross-fertilization of philosophy and physiology, few historians have tried to specify the exact role of philosophers in the evolution of modern psychology. The purpose of this article is to identify one important line of development from within early nineteenth-century German philosophy toward the conception of psychology as an independent, experimental, and mathematical science. The thesis it proposes is that Immanuel Kant's criticism of the psychological tradition and his articulation of a specific philosophy of science provided the negative and positive foundations upon which Jakob Friedrich Fries, Johann Friedrich Herbart, and Friedrich Eduard Beneke developed the conceptualization of scientific psychology.