The Categorical Imperative Universalisability An imperative is a statement of what should be done. We have said before that Hume realised you cant get a should statement out of an is statement. In other words, experience can only give us hypothetical imperatives (If you want to be healthy, then you should exercise and watch what you eat). A description of the way the world is cannot tell us the way we should act.
A Categorical Imperative is a should statement, but it is not based on experience, and doesnt rely on a particular outcome. Rather, it logically precedes experience, or helps us make sense of experience. In another area of thinking, Kant showed that we must presume that time moves forwards our mind imposes this on our experiences to make sense of them. We therefore could never demonstrate or prove this through experience.
It is like that with the categorical imperative: certain actions are logically inconsistent and would make no sense as universal laws, such as lying. As a result, Do not lie is a categorical imperative. This understanding that our mind plays an active role in ordering and shaping our experience was revolutionary, and is Kants greatest achievement.
Kant states the categorical imperative as follows:
I ought never to act except in such a way that I can also will that my maxim should become a universal law.