 As B. Russell pointed out in his Essay on the Foundations of Geometry, Stumpf’s main criticism against Kant and a priori philosophy concerns the dichotomy between form and matter, more precisely the postulate of a priori forms of thought and sensibility. This criticism was already clearly formulated in his Raumbuch, where he examined the nativism-empiricism controversy on space perception, prepared some years earlier by Helmholtz in the third book of his Handbuch. This controversy is at the origin of an important division in the middle of the nineteenth century within the new psychology proponents, between empiricism advocated mainly by Helmholtz and Wundt; and nativism which, according to Helmholtz, characterizes the works of Ewald Hering in physiology, the latter of which in fact exercised an influence on the Brentano school and to a certain extent on Gestalt psychology. Instead of using Helmholtz’s terminology, as did most historians, Stumpf preferred the term phenomenology to designate the study of phenomenal experience, which occupied center stage in the field of physiology and psychology. In his Raumbuch Stumpf takes a stand in favor of a moderate form of nativism, according to which space is a unitary sense, its content is perceptible in an immediate and direct way, and it is inseparable from sensory qualities such as color and sound. Consequently, space and color constitute one and the same content, of which they are partial contents or attributes. They are in a relation of logical dependence with the phenomena of which they form a part. Hence, extension and color form a concrete whole which can only be separated through abstraction. From this point of view, the concept of space, as any concept, draws upon its origin in sense perception and is, to use the Scholastic expression, an abstracta cum fundamento in re.