Posy undertakes to give a precise characterization of the difference between Kant’s critical and precritical philosophy. The need to do this becomes vivid when we notice that many doctrines generally identified with the critical philosophy are already present in Kant’s precritical Inaugural Dissertation (1770). By exposing the Leibnizian roots of Kant’s preoccupation with the metaphysics–mathematics interface, Posy pinpoints the subtle but decisive shift in philosophical standpoint that separates the Critique from the Dissertation.