Epistemological Problems of Quantum Mechanics Following Ernst Cassirer and Richard Hönigswald

This article deals with the Copenhagen interpretation of quantum mechanics and its epistemological discussion by Ernst Cassirer and Richard Hönigswald. The starting point is Cassirer's treatise Determinism and Indeterminism in Modern Physics, published in Stockholm. Both philosophers and several physicists were involved in the subsequent exchange of letters. From a physical point of view, the Copenhagen interpretation was particularly criticised by v. Laue and Einstein. Both demanded a revision of the foundations of quantum mechanics or a critical examination of essential physical concepts. The epistemological implications of the Copenhagen interpretation were rejected, in particular that the interactions between observation, the observed and the observer in quantum physics experiments should lead to a renunciation of the concept of causality or an objectively unambiguous description of natural processes. Cassirer argues here that quantum mechanics fulfils the epistemological requirement of transforming ontological “concepts of things” into epistemological concepts of relations and is therefore compatible with the neo-critical approach he advocates. At the same time, Hönigswald was working on two major treatises on the structure of physics and the concept of causality. Here he undertakes an epistemological foundation of physics as a whole. A transcendental foundation of the concept of experience and its specifications in principles such as contemplation, observation or experiment appears to be called for. Hönigswald therefore essentially rejects the Copenhagen interpretation, as it draws epistemological consequences by physical means and thus inadmissibly reverses the transcendentally necessary relations of justification. These arguments are examined and could be used for a current discussion on the epistemological foundations of quantum mechanics and physics as a whole. A post-Neo-Kantian, transcendental philosophical foundation of scientific knowledge, especially of modern physics, seems possible and necessary.