Comparable copyright limitations can be found in many nations' copyright statutes, though these differ in scope. Most other common law countries have a related doctrine known as fair dealing, which is defined in a constrained manner through an enumerated list of causes for exemption that allows little room for judicial interpretation. Civil law countries have codified similarly specific and narrowly drawn exceptions. Fair use, however, tends to be an open-ended legal doctrine, as statutory factors are balanced by U.S. judges on a case-by-case basis rather than strictly applied.
[A] reviewer may fairly cite largely from the original work, if his design be really and truly to use the passages for the purposes of fair and reasonable criticism. On the other hand, it is as clear, that if he thus cites the most important parts of the work, with a view, not to criticise, but to supersede the use of the original work, and substitute the review for it, such a use will be deemed in law a piracy.
The Folsom court went on to formulate the basis for the factors used today in an analysis of the fair use defense. It continued to be a purely judge-made and applied law until it was finally codified as part of the 1976 Copyright Act at 17 USC § 107, excerpted here:
Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include--
(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
Though according to the Supreme Court, copyright law is not supposed to discriminate based upon the quality or artistic merit of the work at issue, fair use analysis nonetheless looks at whether the copied work was creative or informative. Facts and ideas are unprotected--the particular expression of those facts or ideas is what merits copyrightability. (see idea-expression divide) In application to written works, this factor will tend to weigh for a copying defendant if the original work was a work of nonfiction rather than fiction or fantasy. Functional images--those that are merely illustrative of their subject matter or serve a purely utilitarian purpose--are also more likely to support a finding of fair use than more fanciful, expressive ones.
Also considered critical under this factor is whether or not the original work has been published and/or distributed to the public. Copyright law highly values the author's right to control how his work is first released to the public, and so a work's unpublished nature will tend to weigh against a finding of fair use.
For several years some decisions led many to suppose that one of the few cases where this factor was irrelevant was in sampling a piece of a copyrighted sound recording. Subsequent decisions have shown that this is not the case and a normal fair use analysis must be performed. The US National Association of Music Retailers is one trade group which believes that sampling is not inevitably infringement, in the case of its members when the sample is used as part of the process of selling new or used musical works (position statement).
In regards to the digital reproduction of images it may be argued that a lower resolution sample of the image (i.e. thumbnails) is a lesser sample of the image (the sound recording sample is not analogous here) and thus the whole image is only being approximated by the lower resolution sample (limiting further reproduction outside an informational context) see the Kelly v. Arriba Soft Corporation case below.
Fair use is an affirmative defense to copyright infringement. This means that if the defendant's actions do not constitute an infringement of the plaintiff's rights (for example, because the plaintiff's work was not copyrighted, or the defendant's work did not borrow from it sufficiently), fair use does not even arise as an issue. However, it also means that, once the plaintiff has proven (or the defendant concedes) that the defendant has committed an infringing act, the defendant then bears the burden of proving in court that his copying should nonetheless be excused as a fair use of the plaintiff's work.
Because of the defendant's burden of proof, some copyright owners frequently make claims of infringement even in circumstances where the fair use defense would likely succeed in hopes that the user will refrain from the use rather than spending resources in his defense. Because paying a royalty fee may be much less expensive than having a potential copyright suit threaten the publication of a completed work in which a publisher has invested significant resources, many authors may seek a license even for uses that copyright law ostensibly permits without liability.
Producers or creators of parodies of a copyrighted work have been sued for infringement by the targets of their ridicule, even though such use may be protected as fair use. To be protected as a parody, a work must use the copyrighted material in a manner that is intrinsically a commentary, ridicule, or criticism of it. Fair use will not apply if the use was merely for attention getting.
In Campbell v. Acuff-Rose Music (1994), the Supreme Court recognized parody as a fair use, even when done for profit. Roy Orbison's publisher, Acuff-Rose Music Inc, had sued 2 Live Crew in 1989 for their use of Orbison's "Oh, Pretty Woman" in a mocking rap version with altered lyrics. The Supreme Court viewed 2 Live Crew's version as a ridiculing commentary on the earlier work, and ruled that when the parody was itself the product rather than used for mere advertising, commercial sale did not bar the defense. The Campbell court also distinguished parodies from satire, which they described as a broader social critique not intrinsically tied to ridicule of a specific work, and so not deserving of the same use exceptions as parody because the satirist's ideas are capable of expression without the use of the other particular work.
A recent court case, Kelly v. Arriba Soft Corporation, provides and develops the relationship between thumbnails, inline linking and fair use. In the lower District Court case on a motion for summary judgment Arriba Soft was found to have violated copyright without a fair use defense in the use of thumbnail pictures and inline linking from Kelly's website in Arriba's image search engine. That decision was appealed and contested by Internet rights activists such as the Electronic Frontier Foundation, who argued that it is clearly covered under fair use. On appeal, the 9th District Court of Appeals found that the thumbnails were fair use and remanded the case to the lower court for trial after issuing a revised opinion on July 7, 2003. The remaining issues were resolved with a default judgement after Arriba Soft had experienced significant financial problems and failed to reach a negotiated settlement.
In the U.S., there is also a fair use defense in trademark law based on similar principles as the doctrine under copyright (such as free speech), but with different exceptions. Fair use is consistent with the more limited protection granted to trademarks, generally specific only to the particular product market and geographic area of the trademark owner.
Most trademarks are adopted from words or symbols already common to the culture (such as Apple), instead of being invented by the mark owner (such as Kodak). Courts have recognized that ownership in the mark cannot prevent others from using the word or symbol in these other senses, such as if the trademark is a descriptive word or common symbol such as a pine tree. This means that the less distinctive or original the trademark, the less able the trademark owner will be able to control how it is used.
Trademarks may also be used by a nonowner nominatively--to refer to the actual trademarked product or its source. In addition to protecting product criticism and analysis, U.S. law actually encourages nominative usage by competitors in the form of comparative advertising.
Both of these exceptions require that the mark not be used by the nonowner in a way that would be likely to confuse consumers about the source of their (or the trademark owner's) product. Generally this translates into the requirement, similar to that in fair use under copyright, that no more of the trademark is used than is necessary for the legitimate purpose.