In coming to the consideration of the nature of theory and of the nature of practice we must first determine the sphere in which it is possible to characterize these two modes of relationships to the world. Theory may be described as a special kind of knowledge or cognition; in the classical conception, the essential feature of this kind of knowledge was 'seeing". But when we speak here of knowledge or cognition, we refer to that area of knowledge or cognition in which we shall characterize the nature of theory.