Liberty should be limited only to prevent harm to others

Mill's foundational claim, often called the harm principle, is that the sole legitimate reason for society or the state to interfere with an individual's liberty of action is to prevent harm to other people; a person's own good, physical or moral, is never sufficient justification for coercion. This means society cannot rightly force someone to act in their own best interest — to eat healthily, avoid risky hobbies, or hold correct beliefs — as long as their choices don't damage others. Mill distinguishes this from anarchism: he fully accepts laws against fraud, violence, and other harms to third parties, and even accepts that people can be compelled to perform certain positive duties toward others. His target is paternalism — the idea that authority can override someone's own judgment about their own life for their own supposed benefit. He argues this principle protects not just comfort but the deeper human capacity for self-directed development, since a life managed by others' judgment rather than one's own loses much of its value regardless of outcome. Takeaway: Society may stop you from harming others, but not from making your own mistakes.