Kant believed in the Theory of Duty, and that one’s duty is to perform actions that are morally required of them, so to have the highest form of goodness (Good Will) one must always do their moral duty. Kant argued that all moral decisions should be made upon the grounds of reason and his moral precepts were rooted in rationality, he thought it was wrong for people to be governed by human emotion and feelings (he did not argue against emotion, only being ruled by it). He followed the Categorical Imperative, which is the duty to perform a moral action. It is different to the Hypothetical Imperative which is not obligatory, only conditional. The main difference between them is that the Categorical Imperative is moral and the Hypothetical Imperative is not, thus in order to do your moral duty you must follow the Categorical Imperative. Presupposing freedom is an important part of doing your moral duty, as we are free to make moral choices. So, something that is not possible is not a moral act, therefore if you OUGHT to do something, this implies you CAN, and to do your moral duty, if you ought to do something and you can, then you should.
The Hypothetical Imperative takes the form “if... then...”, e.g. “If you want to get fit you should exercise frequently.” This imperative includes a personal goal and motive, and its outcome is conditional. For example, if you follow the imperative “If you feel guilty when you see a tramp begging for money, then you should give him some”, some days you might be feeling compassionate and when you see the tramp, you feel guilty, so you give him money. However, you may be having a bad day and be in a bad mood, so when you see the tramp you may not feel guilty, and you may feel that he is a nuisance and why should you give him any money? Therefore, the outcome can differ every time you apply it, therefore it is not moral.
The Categorical Imperative