Fair use is a principle in United States copyright law, which permits limited use of a copyrighted work without the permisison of the copyright holder. The classic purposes of "fair use" are to allow commentary, criticism, discussion, and parody of a copyrighted work without the permission of the copyright owner. Fair use is not intented to allow copyrighted content to be used by itself without such permission.
U.S. Law specifies four factors that must be considered when a claim of fair use is made. The law setting them out (Section 107 of the copyright law) reads as follows:
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—
- the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
- the nature of the copyrighted work;
- the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
- 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The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
No one of the factors above is final, all are considered, and fair use determinations are made on a case-by-case basis. Typically any use which serves as a replacement for the original, and thus tends to hinder its market value, is not considered fair use. A use which is "transformative" — that is one which uses the copyrighted material in a very different way from the original, is rather more likely to be considered a fair use then one which is not. Thus a quote from a novel being used to criticise the novel is a transformative use. A copy of a product logo being used to discuss graphic design, or to identify a product being discused, is different from the use of the logo as a marketing tool, and thus is "transformative". A parody is generally transformative. But taking a story and changing the names of characters and the setting, while leaving plot and dialog intact, is not transformative.