Freedom of speech and expression, therefore, may not be recognized as being absolute, and common limitations or boundaries to freedom of speech relate to libel, slander, obscenity, pornography, sedition, incitement, fighting words, classified information, copyright violation, trade secrets, food labeling, non-disclosure agreements, the right to privacy, dignity, the right to be forgotten, public security, and perjury. Justifications for such include the harm principle, proposed by John Stuart Mill in
On Liberty, which suggests that "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."
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The right to freedom of speech and expression is closely related to other rights, and may be limited when conflicting with other rights (see
limitations on freedom of speech) The right to freedom of expression is also related to the right to a fair trial and court proceeding which may limit access to the search for information, or determine the opportunity and means in which freedom of expression is manifested within court proceedings. As a general principle freedom of expression may not limit the right to privacy, as well as the honor and reputation of others. However greater latitude is given when criticism of public figures is involved.
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Freedom of speech is not an absolute right, and legal systems generally set limits on the freedom of speech, particularly when freedom of speech conflicts with other rights and protections, such as in the cases of libel, slander, pornography, obscenity, fighting words, and intellectual property.