Fair use allows individuals to use of copyrighted materials in specific circumstances:
These fair use provisions support the principle of promoting "progress of science and useful arts" (quoted text from the U.S. Constitution, Article 8, Section 1, Clause 8 which lays out the principles of copyright).
Just like copyright itself, fair use has limitations. Those limits are defined in U.S. Copyright Law 17 U.S. Code § 107 and are often called the Four Factors. When evaluating the use of a copyrighted work, these factors determine if the use is acceptable or infringes on copyright. The Four Factors are: