However, this criticism of the Kantian theory of knowledge does not make Stumpf an advocate of psychologism. For Stumpf acknowledges with critical philosophy that we must maintain a strict concept of necessity and thus oppose the reduction of the principles and laws of logic and of science in general to simple empirical generalizations. Stumpf here refers explicitly to J. S. Mill, and maintains that the laws of nature and the principles of logic such as the principle of non-contradiction, for ex