Kant's Fundamental Principles of the Metaphysics of Moral The central concept of Kant's Fundamental Principles of the Metaphysics of Morals is the categorical imperative. “The conception of an objective principle, in so far as it is obligatory for a will, is called a command (of reason), and the formula of the command is called an Imperative.” (Abbott, 30) An imperative is something that a will ought or shall do because the will is obligated to act in the manner in which it conforms with moral law. The categorical imperative is an obligation by the will to act so that the action can be classified as a universal law.