Groundwork of the Metaphysics of Morals: The Categorical Imperative

“Everything in nature works according to laws. Only a rational being has the power to act according to the idea of laws, that is, according to principles; and this power is the will.When reason gives a command to a will that does not always obey it, the command is called an imperative, and it is expressed by the word “ought”.

Now all imperatives command either hypothetically or categorically.A hypothetical imperative says that an action is necessary as a means to something else that one wants: if you want to be healthy, you ought to exercise.A categorical imperative says that an action is necessary in itself, without reference to any other purpose. It does not say “if”; it simply commands.There is therefore only one categorical imperative, namely this: Act only on that maxim by which you can at the same time will that it should become a universal law.

Here is an example. A man finds himself forced by need to borrow money. He knows that he will not be able to pay it back, but he also sees that nothing will be lent to him unless he firmly promises to repay it by a certain time.He wants to make this promise, but he still has enough conscience to ask himself: “Is it not wrong, and against duty, to get out of a difficulty in this way?”Suppose he decides to do it. Then the maxim of his action would be: “When I think I need money, I will borrow it and promise to repay it, although I know that I never can.”

Now I turn this rule of self-love into a universal law, and ask: “How would it be if my maxim were a universal law?”Then I see at once that it could never hold as a universal law of nature, but would necessarily contradict itself.For if everyone in difficulty could promise whatever he liked with no intention of keeping it, promising itself would become impossible. No one would believe anything was promised to him, and everyone would laugh at such statements as empty pretences.”