Kant’s moral argument focuses on reason, good will, duty and the notion that we ought to strive towards moral perfection (Summum Bonum). He believes that people are ruled by a ‘moral law’. This moral law for Kant was universal and objective. An example of this might be seen in the wide scale agreement that murder or torture is wrong. There seems to be agreement across cultures that certain actions are intrinsically wrong. This, for Kant, suggests that there is a universal objective moral law. He believed that the highest form of goodness was the notion of good will, namely that someone would freely choose to do good for no reward whatsoever, only for the sake of goodness. Moreover, Kant believed that we have a moral duty to do such good things. He would argue that we have an awareness of what is right and wrong and that good will should make us act accordingly as reason dictates this to be the case. In a way it doesn’t make any rational sense to act in an immoral way.
Duty was seen by Kant as a way of fulfilling this end without being misguided by emotion or factors of personal gain. It is here that we come to a key point in Kant’s argument, namely the notion of ‘ought’ implies ‘can’. He believed that we can only have a duty to do something that we can do. For example, I cannot have a duty to fly unaided as it is not something that I can do; or if I were to come across someone drowning in a lake but could not swim Kant would suggest that I would not have a duty to jump in and save them. My duty in the latter case would be to find someone who could swim so I would need to raise the alarm. If I can choose to do the good (using reason, good will and duty) in one case then I should be able to do this in every case, moreover that I have a duty to achieve this moral perfection. Kant called this moral perfection the Summum Bonum. He argued that the Summum Bonum was a state of moral perfection existing coincidently with perfect happiness.