Fundamental Principles of the Metaphysic of Morals, The by Immanuel Kant (1724 - 1804)

is Immanuel Kant's first contribution to moral philosophy. It argues for an a priori basis for morality. Where the Critique of Pure Reason laid out Kant's metaphysical and epistemological ideas, this relatively short, primarily meta-ethical, work was intended to outline and define the concepts and arguments shaping his future work The Metaphysics of Morals. However, the latter work is much less readable than the Fundamental Principles. (Summary from Wikipedia)