In this paper I intend to explain why the practical aspects of Kantian metaphysics are obviously the main achievement of his Copernican Revolution. More than that, though: they are the key for understanding the Critical Philosophy itself. Setting off with some remarks on the Critique of Pure Reason, the paper delves into the critique of Practical Reason and ends with the Ceritique of Judgment, thus showing the interconnection of the three masterpieces within a new understanding of human reason as a living organism.
