The author defends utilitarianism by arguing that all moral systems require secondary principles derived from human experience, and that the theory should not be blamed for the inherent complexities of human nature.

The author refutes the claim that utilitarianism is impractical due to lack of time for calculation, arguing that humanity has used its entire history to learn the consequences of actions through experience.

Mill defines the foundation of utilitarianism as the Greatest Happiness Principle, which holds that actions are right if they promote pleasure and wrong if they produce pain.

The author explains how instruments of happiness, such as power or fame, can through association become desired for their own sake and thus transform from mere means into integral parts of an individual's happiness.

Mill argues that because human nature is psychologically driven to desire happiness, it serves as the sole end of human action and the ultimate criterion for morality.