German philosopher who taught at Zürich and founded the epistemological theory of knowledge known as empiriocriticism, according to which the major task of philosophy is to develop a “natural concept of the world” based on pure experience. Traditional metaphysicians believed in two categories of experience, inner and outer, and held that outer experience applies to sensory perception, which supplies raw data for the mind, and that inner experience applies to the processes that occur in the mind, such as conceptualization and abstraction. Avenarius, in his most noted work, Kritik der reinen Erfahrung, 2 vol. (1888–1900), argued that there is no distinction between inner and outer experience, but only pure experience.