Over his career, Kant engages in a long attempt – which reaches a high point in the Prolegomena – to forge what in the Physical Monadology he calls a ‘marriage’ of metaphysics and geometry. The chapter traces the development of Kant’s thought on this union from its pre-critical roots to its flowering in the Prolegomena, and focuses on the role that geometric construction in natural science plays in connecting the two disciplines. This has implications both for how we should understand Kant’s desire to discover the ‘common origin’ of mathematics and natural science that is spelled out in the Prolegomena, as well as how this bears on Kant’s broader views about the status of natural science and laws.

The chapter explores the ways in which Hume’s Dialogues Concerning Natural Religion influenced Kant. Both Hume and Kant have deep reservations about traditional theistic arguments about God, but each declines to reject them entirely, choosing instead to allow that there is some legitimacy in thinking of the world ‘as if’ it were created by God. The essay argues that Kant’s and Hume’s positions are – at least on this issue – much closer than might be expected, particularly in light of Kant’s attempt in the Prolegomena to distance himself from Hume’s attacks on deism.