Immanuel Kant introduced his moral theory in the late 18th century, which sought to establish a supreme principle of morality. He argued that there exists an ethical system whereby moral requirements are requirements of reason, and the rightness of actions is determined by their accordance with moral law. Therefore, an immoral action will always be considered an irrational action. For Kant, a supreme guiding moral principle must carry with it an absolute necessity and be done out of duty to the moral law in order to be free from corruption.
He said that morality is something one ought to abide by unconditionally, that is, without doing so to gain any reward or merit. Kant 's principle is rooted in a concept of duty, and sets forth the requirement that people not merely act in accordance with moral law, but instead for the sake of "pure duty" to following the moral law. He said that duty includes that of a good will, and is "the necessity of an action done out of respect for the law". For example, a shopkeeper faced with the decision of how to price his goods. The shopkeeper can overcharge his customers and receive the increased profits, but this will be an act contrary to moral law. The shopkeeper can also choose to price his goods inexpensively only in order to attract more sales, which will ultimately benefit him as well. However, in this case the shopkeeper would be acting in such a manner in order to reach desirable ends for himself, and not simply for the sake of acting morally, which is still not how morally right people ought to act. Only the shopkeeper who sets fair prices merely because it is the right thing to do for his customers is the man who is acting for the sake of the moral law and is fulfilling his duty to morality.
Kant’s philosophy referred to as the categorical imperative, which is the supreme moral law. Kant therefore
References: 1. http://www.lawandbioethics.com/demo/Main/EthicsResources/Kantian_deontology.htm 2. The Supreme Principle of Morality by Allen W. Wood. 3. Kant’s Search for the Supreme Principle of Morality by Samuel J. Kerstein.