Groundwork for the Metaphysics of Morals (1784) was Kant’s first major ethical treatise, predating the Critique of Practical Reason (1788). Perhaps the most famous and commented upon of all Kant’s ethical works, Groundwork introduced the categorical imperative. Kant says that the true vocation of reason is not to give us the means to some end, but to produce a moral will that is good in itself. He goes on to sharply distinguish actions done from duty from actions done from inclination as the only ones deserving of praise. He says that actions from duty get their moral worth from the worth of the maxim (i.e., rationale) that guides choice, rather than from the worth of the aim of the actions. Duty, he says, is the moral necessity of an action from respect for the law. The relevant kind of law must be universal, and the only thing fitting this requirement is the categorical imperative, which is defined in terms of a pure universality.
Kant goes on to argue that while we are constantly tempted to excuse ourselves from acting in accordance with universal moral duty, no utilitarian, prudential, or other excuses have any place in ethics. Everywhere, he says, “one runs into the dear self, which is always thrusting itself forward”. Any resolution of these issues requires common human reason to move into the field of practical philosophy. To be genuine, morality should hold with absolute necessity, binding for all rational beings. Of course, for Kant this does not mean that our subjective conclusions hold with such necessity. To believe that would be to fall for a trick of the “dear self”, and to claim it would be dogmatism.
For Kant, any genuine supreme principle of morality must depend on pure reason, independent of all experience. We should seek a “fully isolated” metaphysics of morals, “mixed with no anthropology, with no theology, with no physics or hyperphysics”, although its application to human beings also requires anthropology. All moral concepts originate in pure reason. The will, Kant says, is just pure practical reason. (See also The Autonomy of Reason.)