Mill defines utilitarianism as a theory based on the principle that "actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness."

His Utilitarianism (1863) is a closely reasoned attempt to answer objections to his ethical theory and to address misconceptions about it; he was especially insistent that “utility” include the pleasures of the imagination and the gratification of the higher emotions and that his system include a place for settled rules of conduct.

utilitarianism, in normative ethics, a tradition stemming from the late 18th- and 19th-century English philosophers and economists Jeremy Bentham and John Stuart Mill according to which an action (or type of action) is right if it tends to promote happiness or pleasure and wrong if it tends to produce unhappiness or pain—not just for the performer of the action but also for everyone else affected by it.

Mill explains that utilitarianism seeks to increase pleasure in people’s lives, not avoid or prevent it. Mill also clarifies the definition of pleasure; he does not mean pleasure in the form of satisfying animalistic desires, but the higher forms of pleasure that only humans are able to appreciate.