Having investigated the Logical Maxim and the Supreme Principle, Chapter 4 turns to the transition from the former to latter. In a suggestive passage from the Introduction to the Transcendental Dialectic, Kant claims that the Logical Maxim can become a principle of pure reason only by our assuming the Supreme Principle. In order to understand this, we look, first, at the final paragraph of the Introduction, where Kant raises the question of whether the Supreme Principle is ‘objectively valid,’ and then at the Appendix to the Transcendental Dialectic, where he also claims of various ‘logical principles’ that they presuppose ‘transcendental principles,’ which we must therefore ‘assume.’ In light of the distinction between the regulative and the constitutive use of principles, there are two very different ways of understanding what it means to ‘assume’ a principle. Our result will be that the transition to the metaphysical Supreme Principle involves two steps not made explicit by Kant: one from the Logical Maxim to the regulative use of the Supreme Principle, and another from the regulative use of the Supreme Principle to its constitutive use.