While Chapter 3 was dedicated to metaphysical deductions, this chapter reconstructs transcendental deductions, which I take to accomplish the second task of transcendental philosophy as it is established in the Critique of Pure Reason. Transcendental deductions are tasked with determining that root concepts (Stammbegriffe) have objective validity. In a way similar to my analysis of metaphysical deductions, I identify a transcendental deduction of space and time in the Aesthetic, a transcendental deduction of the categories in the Analytic and a transcendental deduction of ideas in the Dialectic. However, objective validity does not mean the same in all these cases. I take it that the main sense in which Kant uses the term is the following: concepts have objective validity when through them we cognize something that really pertains to objects. This is not the sense of objective validity that Kant uses with respect to ideas. In this case, claiming that ideas are objectively valid means attributing to them what I call the ‘practical’ and the ‘indirect’ validity of ideas. I argue that transcendental deductions only establish positive results regarding the validity of the root concepts and are not tasked with determining limits of this validity.