This article addresses a simple question that has rarely been asked of Kant’s philosophy of nature: why are attraction and repulsion the two fundamental forces of matter? Where proposals can be found in the literature, they are divergent. I provide a new answer, which has strong support from the historical context: Kant pursues a modified version of what I call the ‘reduction method’ that was much debated in the German metaphysical tradition. To this, Kant crucially adds his critical doctrine of regulative ideas, revealing an overlooked way that the Appendix to the Critique informs his philosophy of nature.
