The work opens by noting that philosophy has long struggled to establish a definitive criterion for right and wrong, much like the foundational debates found in mathematics and science. Mill sets out to examine and defend the utilitarian theory, which posits that actions are right in proportion to their tendency to promote happiness and wrong as they produce the reverse. He immediately confronts the common objection that viewing pleasure as the ultimate end of life is a doctrine worthy only of swine. In response, he distinguishes between lower physical sensations and higher mental pleasures, arguing that competent judges consistently prefer intellectual pursuits, moral sentiments, and the exercise of higher faculties even when accompanied by discontent.
Moving to potential objections, the author addresses the claim that happiness is unattainable and that humans must learn the virtue of renunciation. He argues that a satisfied life relies on a balance of tranquillity and excitement, supported by mental cultivation and genuine social affections. While genuine heroism may require self-sacrifice, Mill insists that sacrifice is never an end in itself; it derives its moral value entirely from its contribution to the happiness of others. The ultimate standard of utilitarianism is therefore not the agent's own greatest happiness, but the greatest amount of happiness altogether, requiring the individual to remain as strictly impartial as a disinterested spectator.
Mill then explores the internal and external sanctions that give the principle of utility its binding force. External sanctions include the hope of favor and fear of displeasure from others or from God, while the internal sanction is conscience—a subjective feeling of pain linked to the violation of duty. He argues that this moral feeling is a natural outgrowth of human social instincts and the desire for unity with fellow creatures, reinforced by education and civilization. Because human beings are inherently social, the habit of coordinating interests and pursuing collective well-being naturally strengthens over time, providing a solid foundation for utilitarian ethics.
The discussion turns to the proof of the principle of utility, where Mill acknowledges that ultimate ends do not admit of proof in the ordinary sense. Just as the only evidence that something is visible is that people see it, the sole evidence that something is desirable is that people actually desire it. While humans desire things like virtue, money, and power, these objects either become integral parts of happiness or serve as means to achieve it. Ultimately, human nature is so constituted that nothing is desired except happiness itself, making the promotion of general happiness the ultimate test of all human conduct.
In the final section, the author tackles the complex relation between utility and justice. Many critics view justice as an absolute standard independent of expediency, but Mill demonstrates that justice represents a collection of moral rules more vital to human well-being than any other. The sentiment of justice originates from the natural impulse of self-defence and sympathy, combined with a demand for punishment when rights are violated. Because security is the most indispensable of all human needs, the rules protecting it assume an absolute character that distinguishes them from ordinary expediency. Ultimately, all maxims of equality and distributive justice trace back to the foundational utilitarian principle that equal amounts of happiness are equally desirable for every individual.
