"Fair use" is a legal exception to copyright control. Common examples of fair use include copying or quoting for the purposes of commentary, criticism, research, scholarship, news reporting, and classroom teaching.

Four factors must be balanced in each case to determine whether a specific use is fair:

1. The purpose and character of the use — whether the new use is commercial, nonprofit, or educational, among other relevant characteristics; and whether it is "transformative" or merely substitutes for the original. For-profit enterprises generally have less latitude as to the "fairness" of their use than do non-profit enterprises. More important than commerciality is whether a use is "transformative" or merely substitutes for the original work. A use that transforms the original in some way — for instance, a book review that quotes the original, a parody that references it, or documentary film that uses archival footage — is "fairer" than a use that merely substitutes for the original.
    
2. The nature of the original work — whether the original work is factual or creative; published or unpublished; in or out of print. Because copyrights don't protect "facts" or "ideas", but only "expression", if a work is primarily factual, then uses of the work are more likely to be considered fair. Indeed, if a work is only a compilation of facts, it is not protected by copyright at all, although the selection or organization of material might be original enough to have a copyright.
    
3. How much, and how substantial a part, of the original was taken — whether more was taken than needed, or whether the "heart of the work" was taken. The less of a work that is taken, the more likely it is to be fair. But even the whole work can be taken, if it is for a fair and legitimate purpose.
    
4. The effect of the new use on the market for or value of the original work — whether the new use substitutes for the original work in the commercial marketplace, or reduces its value by supplanting demand for the original. Deciding whether a new work undermines the value of, or market for, the original, of course depends on the first fair use factor — what is the purpose and character of the new work? Is it "transformative", or in some other way not a substitute for the original? It also depends on the third fair use factor — whether the original work is wholly appropriated, or less of it is taken.

Each of these four factors is open-ended. In different copyright cases over the years, courts have supplied interpretations, developed nuances, and applied the factors in ways that help us decide what uses are "fair". Decades of court interpretations define what is meant by fair use today. A fair use exception is most likely to be granted under the following conditions:

1. the use is for non-commercial purposes;
2. the original work was inexpensive to produce and/or distribute;
3. a relatively small amount of the original work is used;
4. the portion used is transformed, not merely copied; and
5. the economic impact is insignificant.

This article was derived in part from: Fair use of copyrighted material, Fair Use Network, the Brennan Center for Justice at NYU School of Law, 161 Avenue of the Americas, 12th Floor New York, NY 10013.

NOTICE: This article discusses general legal issues of interest and is not designed to give any specific legal advice pertaining to any specific circumstances. It is important that professional legal advice be obtained before acting upon any of the information contained in this article.

Further reading

• Fair Use Network by the NYU Brennan Center for Justice, Free Expression Policy Project
• Fair Use of Copyrighted Materials by the University of Texas System Office of General Counsel
• Fair Use in a Nutshell: A Roadmap to Copyright's Most Important Exception – By Lloyd J. Jassin; from CopyLaw.com
• Limitations on exclusive rights: Fair use – From the US Copyright Office
• A guide to the circumstances of fair use – From the University of Texas at Austin "Copyright Crash Course" program.
• Fair Use: Copyright Management Center, with Copyright Essentials including a fair use checklist.