In a passage in both editions of the Critique of Pure Reason, Kant describes what he wants to accomplish there as a ‘doctrine of method’ (A82–3/B108–9). In the B-Preface, he adds that the Critique ‘is a treatise on the method’ (Bxxii). In this chapter, I argue that the best way to understand these claims is to see them as an indication that the Critique is the doctrine of method of metaphysics. I start by clarifying what a doctrine of method is for Kant and distinguish between the doctrine of method of general logic and the doctrines of method of particular sciences. In a second step, I argue that the Transcendental Doctrine of Method is the particular doctrine of method of metaphysics. Furthermore, I explain how this is compatible with regarding the whole Critique as the doctrine of method of metaphysics. Since cognitions belonging to a science must already be established in order for a doctrine of method to perform its task, the Transcendental Doctrine of Method requires that at least some doctrinal parts of metaphysics be established in the Transcendental Doctrine of Elements. I argue that this has important consequences for how we should depict the relationship between the critique of pure reason and transcendental philosophy.

In the Architectonic of Pure Reason, Kant claims that a condition for attaining the status of science is that a body of cognitions achieves architectonic unity. The chapter clarifies what this is and argues that this is more than mere systematicity. While there could be different ways of systematically ordering a body of cognitions, there is only one such order that bestows architectonic unity to it. Architectonic unity is achieved when the ‘idea’ of a science given a priori by reason is realized in an actual body of cognitions. I read this ‘idea’ as the correct description of the body of cognitions that form a science and its parts–whole relationships. In a further step, I discuss the ‘idea’ that is a candidate for providing unity to metaphysics. Kant identifies two candidate ‘ideas’ according to which metaphysics can be understood. Metaphysics can be construed according to either the ‘school concept’ (Schulbegriff) or the ‘worldly concept’ (Weltbegriff) of philosophy. I argue that it is only according to the ‘worldly concept’ that metaphysics can attain architectonic unity and become a science.