Fair use, as defined in Section 107 of the Copyright Act, allows, in certain cases, the legal (non-infringing) use of copyrighted works without the need to obtain permission from the copyright holder. It is important to understand that what counts as fair use of copyrighted material is subjective and must be determined case by case. While the following four factors are guidelines for fair use, there are no hard-and-fast rules for determining when a specific use of copyrighted material is fair versus when it is an infringement of copyright.
The Four Factors of Fair Use
Four factors are considered when determining whether on not fair use applies.
1. The purpose and character of the use.
2. The nature of the copyrighted work.
3. The amount and substantiality of the portion taken.
4. The effect of the use upon the potential market.
Before explaining what each of the factors mean in practice, it is important to note that each of the four factors are considered equal in determining fair use and all four factors must be considered as a whole. This means that even if a use of a copyrighted work is not considered fair use based on one factor, when the other factors are weighed that use could still be considered fair.
Say, for example, you wanted to share the entirety of a copyrighted article with students in your class. Using the entire article would weigh against fair use factor number 3. However, if the other three factors weighed heavily in favor of fair use, then sharing the article could be considered fair use. As mentioned above, determining fair use is subjective, and what one person sees as fair use, another may not.
You can use the UC Merced Checklist for Fair Use to help determine if an intended use of copyrighted material is or is not fair use.
The Stanford University Copyright & Fair Use website provides a thorough overview of what the four factors of fair use mean in practice. What follows is a summary explanation:
1. The Purpose and Character of the Use
In general, using copyrighted material for non-profit educational purposes is more likely to be considered fair use than using it for a commercial purpose. This does not mean, however, that non-profit educational use is automatically considered fair use. For one example, if a commercial work has been created specifically for the educational market--as is the case with textbooks--then it is unlikely that use of the work in an educational setting (whether non-profit or for-profit) will be considered fair use.
Another element of character and use is whether or not the use is transformative. For a use to be transformative, it must create something new rather than being a cut-and-paste copying of the copyrighted material. One example of transformative use is parody, as when "Weird Al" Yankovic transforms a serious song into a comical song by setting new words to the original music and, typically, rearranging the instrumentation. Another example of transformative use is criticism, as when an art critic uses an image of a copyrighted painting in order to comment upon it. Similarly, using a portion copyrighted work for research, education, news reporting, or scholarship can be considered transformative. A philosophy professor's use of a clip from the Three Stooges' 1941 film So Long Mr. Chumps to make a point about Nietzsche's concept of the Übermensch is likely to be considered transformative because such a use is far removed from the original comedic purpose of the film. As is true of every fair use factor, whether or not a use is transformative is a judgment call.
2. The Nature of the Copyrighted Work
If a work is non-fictional/factual, use of it is more likely to be considered fair use than if the work is fictional/creative. This means that using a copyrighted non-fiction scholarly article about Nietzsche's concept of the Übermensch is more likely to be considered fair use than is the use of the fictional film So Long Mr. Chumps.
Also, use of a work that has been published is more likely to be considered fair use than is use of an unpublished work.
3. The Amount and Substantiality of the Portion Taken
As a rule, the smaller the portion of a work that you use, the more likely it is to be considered fair use. Using a fifteen-second clip from So Long Mr. Chumps (total length 17' 23") is more likely to be considered fair use than is using a five-minute clip from the same film.
However, if you use what is considered the "heart of the work," that use is unlikely to be considered fair use even if the amount used is very small. For example, suppose the five-seconds of So Long Mr. Chumps that you use consists of the scene of Moe bopping Curly in the nose. If the copyright holder of So Long Mr. Chumps successfully argues that this one bop in the nose is the heart of the film, your brief use might not be considered fair use. For another example, (spoiler alert) posting the paragraph from Harry Potter and the Deathly Hallows which reveals Severus Snape's unrequited love for Lily Potter might not be considered fair use on the grounds that this paragraph, though only a small part of a novel that runs some 600 pages in length, comprises the heart of the novel (if not of the entire series of seven novels).
On the other hand, in cases where use of the entire work is essential, such as with the study of photographs and paintings, use of the entire work may be considered fair use. So too, a parody may be considered fair use even if it uses the entirety of a work.
4. The Effect of the Use Upon the Potential Market
If a copyrighted work is readily available so that you could reasonably purchase or license it, then use of the work is less likely to be considered fair use than if it is not readily available. A book you can order a new copy of via Amazon.com or pick up at a local bookstore? Probably not fair use to post a copy on your course website. A book that has been out of print so long that new copies have not been available for forty years? Fair use is the more likely verdict.
How you use a work also factors into effect upon the potential market. Making the entirety of So Long Mr. Chumps available via a password-protected course management system so that only the twenty-five students enrolled in the course you are teaching can access it could be seen as having insignificant effect upon the potential market. On the other hand, openly posting a copy of the same film on YouTube so that you can profit from advertising revenues would very likely be seen as having a big effect on the potential market and so not be considered fair use.
While all four factors of fair use are considered equally important, in the unlikely event a copyright lawsuit ends up in court the effect upon the potential market may be seen as the deciding factor in the eyes of a judge or a jury.