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."

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.

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 is the theory that laws and actions should be judged as good or bad based on their utility, meaning the results they produce. For a utilitarian, the best actions or laws are those that produce the greatest good for the most people, and the greatest good over the least amount of pain.

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.