 In light of this distinction, one can better understand the significance of the debate on psychologism such as Stumpf describes it in his 1891 paper. Stumpf opposes two schools of thought on the question of the relationship between the theory of knowledge and psychology: Kantian criticism that dissociates the theory of knowledge from psychology, and psychologism which Stumpf defines in this paper as “the reduction of all philosophical investigation, and especially all epistemological investigations, to psychology.” (Stumpf, 1891, p. 468) The argument in favour of psychologism boils down to the idea that “knowledge is itself a mental process and accordingly the study of its conditions would be a psychological investigation.” (Stumpf, 1891, p. 468) Critics of psychologism, on the other hand, argue that a psychological investigation can never lead to “knowledge of general and necessary truths.” (Stumpf, 1891, p. 469) Now since the conditions of possibility of knowledge, i.e. the forms of intuition and thought, are themselves a priori and therefore not analysable (Stumpf, 1891, p. 493), psychology is therefore useless for Kantian criticists.