Mill refined Bentham's utilitarianism by arguing in "Utilitarianism" (1863) that pleasures differ in quality as well as quantity, so that higher intellectual and moral pleasures count for more than lower bodily ones ("it is better to be a human being dissatisfied than a pig satisfied"). In "On Liberty" (1859) he defended individual liberty against social and state control through the harm principle, and in "The Subjection of Women" (1869) he argued for full legal and social equality between the sexes.
Intellectual setting
Mill wrote as heir to the Benthamite utilitarian tradition instilled by his father's rigorous childhood education, later revising its psychological and ethical assumptions after his own documented mental crisis and his intellectual partnership with Harriet Taylor Mill, whom he credited as a major influence on his political and feminist thought.
Key ideas
Qualitative hedonism
Against Bentham's purely quantitative treatment of pleasure, Mill argued that pleasures differ in kind as well as amount, and that competent judges who have experienced both consistently prefer higher intellectual and moral pleasures to lower bodily ones, even at a cost in quantity.
The harm principle
In "On Liberty," Mill argued that the only legitimate reason for society or the state to interfere with an individual's liberty of action is to prevent harm to others, not to enforce morality or promote the individual's own good against their wishes.
Legacy
Mill's "On Liberty" remains a foundational text of modern liberalism and free-speech theory, and "The Subjection of Women" is a founding text of liberal feminism; his qualitative utilitarianism continues to structure debates in contemporary ethical theory.