Fair Use* is determined by a balanced application of four factors set forth in the statute:
(1) the purpose of the use; (2) the nature of the work used; (3) the amount and substantiality of the work used; and (4) the effect of the use upon the potential market for or value of the work used.
The purpose of the use:
Nature of the Work
Amount and Substantiality of the Work Used
Effect of the Use on the Value of the Work Used
*A more elaborate statement of Fair Use may be found at the website of the U.S. Office of Copyright at: https://copyright.gov/fair-use/