The common law traditionally presumed that a statement was false once a plaintiff proved that the statement was defamatory. Under modern law, a plaintiff who is a public official or public figure must prove falsity as a prerequisite for recovery. Some states have likewise now provided that falsity is an element of defamation that any plaintiff must prove in order to recover. Where this is not a requirement, truth serves as an affirmative defense to an action for libel or slander.

A statement does not need to be literally true in order for this defense to be effective. Courts require that the statement is substantially true in order for the defense to apply. This means that even if the defendant states some facts that are false, if the “gist” or “sting” of the communication is substantially true, then the defendant can rely on the defense.