Hermann Cohen and Alois Riehl on Geometrical Empiricism

When non-Euclidean geometry was developed in the nineteenth century, both scientists and philosophers addressed the question as to whether the Kantian theory of space ought to be refurbished or even rejected. The possibility of considering a variety of hypotheses regarding physical space appeared to contradict Kant’s supposition of Euclid’s geometry as a priori knowledge and suggested the view that the geometry of space is a matter for empirical investigation. In this article, I discuss two different attempts to defend the Kantian theory of space against geometrical empiricism. Both Cohen and Riehl defended the apriority of geometrical axioms. Cohen pointed out that knowledge necessarily requires both sensibility and understanding. Therefore, he maintained that space can be proved to be a condition of experience without admitting that some statements about it are intrinsically necessary. By contrast, Riehl emphasized universality and necessity as intrinsic properties of a priori knowledge. He was one of the first philosophers to discuss the space problem in detail and to distinguish between a priori properties of space and empirical properties. Nevertheless, I suggest that Cohen developed a more plausible view because he was not committed to any spatial structure independently of empirical science.