Utilitarianism

Jeremy Bentham, the founder of Utilitarianism, based his philosophy on this claim: "Nature has placed mankind under the governance of two sovereign masters, pain and pleasure. It is for them alone to point out what we ought to do, as well as to determine what we shall do. The said truth is that it is the greatest happiness of the greatest number that is the measure of right and wrong."

As an empiricist, he had to base his moral philosophy on observations of people’s actual behavior, falling into the error of claiming that what people actually do is a basis for deciding what people should do.  But there is an even more obvious error here.

Nature impels us to seek pleasure and avoid pain for ourselves and for a small number of relatives and friends, but nature obviously does not impel us to believe that everyone else’s pain and pleasure is as important as our own. In fact, hedonist philosophers before Bentham’s time, such as the Epicureans, based their ethics on pain and pleasure one’s acts cause to oneself, not to others.

How does Bentham jump from the empirical observation that people seek pleasure and avoid pain to themselves to the moral judgment that people should maximize pleasure and minimize pain for everyone?  There is obviously another principle that we do not know empirically added to the empirical observation that we people seek pleasure and avoid pain - something like “we should consider all people to be equally important” or “we should do unto others as we would have others do unto us” - and this added principle is not known by empirical observation of people’s usual behavior.

If this moral principle can be known by other means than observation, then it is plausible that other moral principles might be known by other means than observation - including principles that override the idea that the goal of life is to maximize pleasure and minimize pain.