What is the test for fair use in copyright law?

The Copyright Act of 1976, 17 U.S.C. Secs. 101-810 (1982) grants the owner of an original work the sole right to use and to authorize use of that work. Id. Sec. 106. The principal purpose of the legislation is to encourage the origination of creative works by attaching enforceable property rights to them. Absent such property rights, creation would be discouraged by the ease of reproduction and use without the permission of the author. However, concern that the public interest in the development of intellectual property would be impaired by overly rigid restrictions on dissemination led early on to the development of a judge-made defense of "fair use". This defense focused primarily on the injury to the copyright owner and whether "so much is taken, that the value of the original is ... diminished, or the ... original author['s labors] are substantially to an injurious extent appropriated by another." Folsom v. Marsh, 9 F.Cas. 342, 348 (C.C.D.Mass.1841) (No. 4,901) (Story, J.).

The Copyright Act of 1976 codified this judge-made doctrine in Section 107 which provides in pertinent part: