Kantian ethics refers to a deontological ethical theory developed by German philosopher Immanuel Kant that is based on the notion that: "It is impossible to think of anything at all in the world, or indeed even beyond it, that could be considered good without limitation except a good will." The theory was developed in the context of Enlightenment rationalism. It states that an action can only be moral if (i) it is motivated by a sense of duty and (ii) its maxim may be rationally willed a universal, objective law. Central to Kant's theory of the moral law is the categorical imperative. Kant formulated the categorical imperative in various ways. His principle of universalizability requires that, for an action to be permissible, it must be possible to apply it to all people without a contradiction occurring. Kant's formulation of humanity, the second section of the categorical imperative, states that as an end in itself, humans are required never to treat others merely as a means to an end, but always as ends in themselves. The formulation of autonomy concludes that rational agents are bound to the moral law by their own will, while Kant's concept of the Kingdom of Ends requires that people act as if the principles of their actions establish a law for a hypothetical kingdom. The tremendous influence of Kant's moral thought is evident both in the breadth of appropriations and criticisms it has inspired and in the many real world contexts in which it has found application. Outline Although all of Kant's work develops his ethical theory, it is most clearly defined in Groundwork of the Metaphysics of Morals, Critique of Practical Reason, and Metaphysics of Morals. As part of the Enlightenment tradition, Kant based his ethical theory on the belief that reason should be used to determine how people ought to act. He did not attempt to prescribe specific action, but instructed that reason should be used to determine how to behave. Good will and duty In his combined works, Kant constructed the basis for an ethical law by the concept of duty. Kant began his ethical theory by arguing that the only virtue that can be unqualifiedly good is a good will. No other virtue has this status because every other virtue can be used to achieve immoral ends (for example, the virtue of loyalty is not good if one is loyal to an