Certainty and Practical Reason is concerned with Kant's practical response to epistemological skepticism and radical doubt. ;It begins from Kant's remark that the concept of freedom is the keystone of the arch of reason, theoretical as well as practical, and sustains reason against skepticism; and from Kant's account of the practical motives of transcendental realism, the source of skepticism, in the First and Second Critiques. The Critiques suggest both that Kant's response to skepticism is practical, and that skepticism is itself (...) both practically motivated and associated with practical error. ;In the first chapter, it is argued that the Transcendental Analytic of the First Critique is not a final refutation of skepticism and radical doubt, and that Kant does not see it as such. The theoretical arguments of the Transcendental Analytic need to be completed with an appeal to practical reason if we are to ground Kant's starting assumption, the fact of experience. ;The second chapter considers epistemological skepticism as involving a practical error answered by the practical cure of the categorical imperative. ;The third chapter begins by considering Cartesian doubt as a practically motivated attempt to pose the problem of practical rationality, and Kant's response to this problem. It then discusses Kant's view that the transcendental realist demand for knowledge of the noumenal, which gives rise to skeptical doubt, is a pursuit of the unconditioned whose hidden meaning is practical; and explains how Kant responds to the doubt by responding to and interpreting transcendental realism as a practical project. ;The fourth chapter discusses the Critique of Judgment as a response to "enthusiasm" or the transcendental realist claim to knowledge of the unconditioned, and thereby to skepticism as well. (shrink)