Kant's Categorical Imperative
"Act only according to that maxim whereby you can
at the same time will that it should become a universal law." -- Kant
http://www.philosophypages.com/hy/5i.htm
"The essence of immorality, then, is to make an exception of myself by
acting on maxims that I cannot willfully universalize. It is always wrong to act
in one way while wishing that everyone else would act otherwise. (The perfect
world for a thief would be one in which everyone else always respected private
property.) Thus, the purely formal expression of the categorical imperative is
shown to yield significant practical application to moral decisions.
...
Kant offered the "formula of the end in itself" as: "Act in such a way that you treat humanity, whether in your own person or in the person of another, always at the same time as an end and never simply as a means." This places more emphasis on the unique value of human life as deserving of our ultimate moral respect and thus proposes a more personal view of morality. In application to particular cases, of course, it yields the same results: violating a perfect duty by making a false promise (or killing myself) would be to treat another person (or myself) merely as a means for getting money (or avoiding pain), and violating an imperfect duty by refusing to offer benevolence (or neglecting my talents) would be a failure to treat another person (or myself) as an end in itself. Thus, the Kantian imperative agrees with the Christian expression of "The Golden Rule" by demanding that we derive from our own self-interest a generalized concern for all human beings.
Drawing everything together, Kant arrived at the "formula of autonomy," under which the decision to act according to a maxim is actually regarded as having made it a universal law. Here the concern with human dignity is combined with the principle of universalizability to produce a conception of the moral law as self-legislated by each for all. As Kant puts it,
'A rational being belongs to the kingdom of ends as a member when he legislates in it universal laws while also being himself subject to these laws. He belongs to it as sovereign, when as legislator he is himself subject to the will of no other.
A rational being must always regard himself as legislator in a kingdom of ends rendered possible by freedom of the will, whether as member or as sovereign.'"