Mill, John Stuart: Utilitarianism, v1, IMP, 22 Dec 2007.
 

A philosophical classic.

Wikipedia notes:
The canonical statement of Mill's Utilitarianism can be found in Utilitarianism. This philosophy has a long tradition, although Mill's account is primarily influenced by Jeremy Bentham, and Mill's father James Mill. Mill’s famous formulation of Utilitarianism is known as the "greatest happiness principle." It holds that one must always act so as to produce the greatest happiness for the greatest number of people. One of Mill's major contributions to Utilitarianism is his argument for the qualitative separation of pleasures. Bentham treats all forms of happiness as equal, whereas Mill argues that intellectual and moral pleasures are superior to more physical forms of pleasure. Mill distinguishes between "happiness" and "contentment," claiming that the former is of higher value than the latter, a belief wittily encapsulated in his statement that it is better to be Socrates dissatisfied than a fool satisfied.