"The only purpose for which power can be rightly exercised over any member of a civilized community against his will, is to prevent harm to others."--John Stuart Mill, On Liberty.

The harm principle is a theory by British philosopher John Stuart Mill that states that a government or society does not have the right to prevent people from actions unless the actions are harmful to others in society. Behavior or actions that do not affect or harm others should not be subject to government or legal scrutiny. Under this principle governments do not have the right to construct laws that protect the individual from actions that may do harm to on himself/herself. While this would seem to create an anarchy or free-for-all, Mill closely associates the principle of utility to his harm principle.

“My right to swing my arm ends where your nose begins.” --Zechariah Chafee, American judicial philosopher

The principle of utility commands that people make decisions based on how those decisions will bring the greatest amount of happiness to the most people. When making a decision between two different paths, the person making the choice should choose the direction that will please the most people. Mill understands that it is very rare for an action to not have an effect on others because all people in society are interconnected through various social systems.

Mill also takes care to define what is meant by "harm." Harm is not an action that simply offends others but actually interferes with the rights, interests, and benefits of another person. Having said that, Mill believed that the freedom of speech was one right that should be protected under the harm principle.