On a standard reading, a major result of Kant’s critical philosophy is the demotion of theoretical reason to a merely ideal and regulative role. Yet Kant also maintains that there is a legitimate real use of pure reason which survives critique and indeed is indispensable although his treatment of this topic is scattered and less well discussed than his negative remarks. This essay seeks to do justice to the systematic ambition of Kant’s positive account of theoretical reason. The real use of reason can be reduced neither to a mere empirical aid to science, nor to a source of merely ‘ideal’ speculations, nor to a purely logical framework for theory construction – even as reason does also play each of these roles.
Part I provides a taxonomy and evaluation of Kant’s systematic theory of the real use of reason, focusing in turn on reason’s conative, cognitive, and explanatory aspects. Special attention is given to case studies in Kant’s treatment of the physical and life sciences. Through a historical and contextual reconstruction beginning with his earliest works, Part II explores Kant’s critique of earlier accounts of reality, natural purposiveness, and of theoretical and practical accounts of the world. In each case, Kant does not simply abandon the heritage of rationalist metaphysics, but provides it with a new and systematic justificatory framework: his own account of theoretical reason as a faculty that can think absolute totality.