Abstract

The achievement of Immanuel Kant lies in demonstrating the law-giving power of the human intellect in the metaphysical basis of human cognition and in defence of human freedom. The power of reason was his response to the mechanical view of nature and scepticism in morals, aesthetics and religion. While reason extended over theory and practice, it was, he insisted, one reason: a unity. I advocate the unity of reason as key to understanding Kant’s philosophical project. Given his huge output, this is an inevitably incomplete ambition. After an introductory chapter, comes an explication of the key role of the maxim followed by proposing a three-fold understanding of reason itself with its ideas and postulates. These extend our theoretical and practical knowledge in reason’s differing interests, albeit with conceptual difficulties in motivation and respect. Despite different faculties, theoretical and practical reason cannot conflict for there are not two reasons. One must have primacy which is shown to be the practical. The latter doctrine has implications for Kant’s rational theology and his broader world view. Morality’s supreme principle, a product of universalised reason, highlights the destiny of humankind and leads to a moral faith unique to humans. By virtue of reason, we have the will to realise our final end. The justification of reason’s unity leads to the regulative idea of a highest intelligence as a heuristic. Kant’s moral philosophy culminates in the concept of the highest good as the final end of human life. I discuss its secular and religious interpretations before concluding that, for Kant, we belong not only in the world of nature but in a noumenal world in which God and a future life may be the hope of our finite reason.