"Truth" is an absolute defense against defamation. See New York Times Co. v. Sullivan, 376 U.S. 254 (1964), and Time Inc. v. Hill, 385 U.S. 411 (1967). Consequently, a plaintiff has to provide convincing evidence of a defamatory statement's falsity in order to prove defamation.
The law does not require that a statement must be perfectly accurate in every conceivable way to be considered "true." Courts have said that some false statements must be protected for the wider purpose of allowing the dissemination of truthful speech. The resulting doctrine is known as "substantial truth." Under the substantial truth doctrine, minor factual inaccuracies will be ignored so long as the inaccuracies do not materially alter the substance or impact of what is being communicated. In other words, only the "gist" or "sting" of a statement must be correct.
The substantial truth defense is particularly powerful because a judge will often grant summary judgment in favor of a defendant (thus disposing of the case before it goes to trial) if the defendant can show that the statement the plaintiff is complaining about is substantially true, making the defense a quick and relatively easy way to get out of a long (and potentially expensive) defamation case.
Substantial truth can also be a flashpoint for libel cases involving public figures and officials who must show actual malice by the defendant in order to recover. In Masson v. New Yorker Magazine, 501 U.S. 496 (1991), the plaintiff tried to argue that inaccurate quotations were evidence of actual malice. The Supreme Court refused to adopt such a stringent rule, noting the difficulty of taking notes and translating from recordings and the need to edit a speaker's comments into a coherent statement. The Court stated: