Introduction

'Two things fill the mind with ever new and increasing admiration and awe, the more often and steadily we reflect upon them: the starry heavens above me and the moral law within me.' These words, carved on Kant's tombstone, come from the conclusion of the Critique of Practical Reason. The first Critique showed that reason cannot know freedom, the immortality of the soul and God theoretically; the second shows that reason in its practical use, in moral action, can establish them. The moral law is an unconditional command that reason gives itself, and in being conscious of it we are conscious of our freedom. To make possible the highest good, in which virtue is matched by happiness, we must postulate the immortality of the soul and the existence of God. The book develops Kant's moral philosophy more systematically than the Groundwork.