Kant invented the categorical imperative, which is a tool that can be used to understand whether certain maxims are rational or not. Kant formulated the categorical imperative in two different ways: the formula of humanity and the universal formula. “Act only according to that maxim by which you can at the same time will it to become a universal law.” This is Kant's universal formula, which one should use and reflect on before carrying out a certain action. This means that one should perform an action only if one believes that this particular action can be used as a universal law. In other words, only if he believes that we can get out safely into a world where everyone could repeat the same action. Dr. Arnold used the example of promises. If Tim makes promises to Ben but doesn't intend to keep them. He should think about what the world will be like if everyone makes promises that they don't intend to keep, after a certain time no one will ever believe the promises