 Kant had delivered the latest grand attempt to address the relation between science and philosophy, by taking the former to provide objective empirical knowledge (exact, universal and necessary) and giving to the latter knowledge the task of laying out the conditions of intelligibility and possibility of such knowledge as the sole, critical scope of metaphysics and legitimate exercise of reason. Kant’s standard of a priori, an expression of rationality, was challenged and relativized by the Frege, Russell and Whitehead’s notions of mathematical numbers grounded in logic and by the new notions of space and time in Einstein’s relativity theories. Neither mathematics was synthetic, nor physics seemed a priori; and the synthetic a priori was dismissed as empty of content in the new scientific landscape.