 Cassirer’s next important contribution to scientific epistemology [Cassirer 1921] explores the relationship between Einstein’s general theory of relativity and the “critical” (Marburg neo-Kantian) conception of knowledge. Cassirer argues that Einstein’s theory in fact stands as a brilliant confirmation of this conception. On the one hand, the increasing use of abstract mathematical representations in Einstein’s theory entirely supports the attack on Aristotelian abstractionism and philosophical empiricism. On the other hand, however, Einstein’s use of non-Euclidean geometry presents no obstacle at all to our purified and generalized form of (neo-)Kantianism. For we no longer require that any particular mathematical structure be fixed for all time, but only that the historical-developmental sequence of such structures continuously converge. Einstein’s theory satisfies this requirement perfectly well, since the Euclidean geometry fundamental to Newtonian physics is indeed contained in the more general geometry (of variable curvature) employed by Einstein as an approximate special case (as the regions considered become infinitely small, for example). Moritz Schlick published a review of Cassirer’s book immediately after its first appearance [Schlick 1921], taking the occasion to argue (what later became a prominent theme in the philosophy of logical empiricism) that Einstein’s theory of relativity provides us with a decisive refutation of Kantianism in all of its forms. This review marked the beginnings of a respectful philosophical exchange between the two, as noted above, and it was continued, in the context of Cassirer’s later work on the philosophy of symbolic forms, in [Cassirer 1927b] (see [Friedman 2000, chap. 7]).