Motivational Kantianism: Cassirer's late shift towards a regulative conception of the apriori

Cassirer often pointed out that the physics of his time had progressively become a 'physics of principles' rather than a 'physics of models'. Until the 1920s, Cassirer regarded these principles (the energy principle, the relativity principle etc.) as a constitutive but provisional form of the a priori, imposing specific limitations on the form of the allowable laws of nature. This paper argues that Cassirer shifted the role of the a priori to a deeper level in the 1930s. The a priori acquires a regulative meaning, motivating the search for the laws of nature without providing any particular insight into their form. The paper contends that, in this way, Cassirer embraced what might be called a 'motivational Kantianism'. It can be argued whether this stance still deserves to be called a form of 'neo-Kantianism'. However, depriving the a priori of any specific content allowed Cassirer to attribute a constitutive role to 'statements of principle' without granting them a priori status. This paper concludes that this attitude towards the role of 'principles' in physics sets Cassirer's philosophy apart from its positivist and post-positivist counterparts.