How is fair use determined? What are the “four factors”?

There is no simple formula or method to easily determine whether a particular use of a copyrighted work is a fair one.

The copyright statute gives us four factors to apply on a case-by-case basis:

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.
4. The effect of the use upon the potential market for or value of the copyrighted work.

The four factors are more than a checklist. They have to be analyzed at an individual level and taken together as a whole, but they might be weighted differently depending on the facts of your particular case.

Courts use these factors to decide whether a particular use qualifies, but remember that they can only do so after you have been sued for copyright infringement. The burden of establishing the fair use exception always falls on the person asserting it; the copyright holder does not have to prove the lack of fair use.