Chapter 3 turns to the fundamental metaphysical concept in Kant, the concept of the ‘really’ (not just logically) unconditioned, and to the conditioning relations between objects that speculative metaphysics tracks. Kant’s Rational Sources Account (his argument that the sources of speculative metaphysics lie in reason itself) rests on the claim that the logical use of reason naturally leads us to accept a principle he calls the “supreme principle of pure reason.” In this chapter, we will try to clarify this principle by asking what Kant, in the context of the Supreme Principle, means by ‘given,’ by ‘the conditioned’ and its ‘conditions,’ what it means for something to be ‘unconditioned,’ and why Kant thinks the series of subordinated conditions is supposed to be unconditioned in this sense. Finally, we will ask how that principle relates to the Principle of Sufficient Reason.