What is the American approach to assessing "fair use" in copyright law?

The American approach is called “fair use”. The U.S. Code provisions create an open set of purposes for fair use which include criticism, comment, news reporting, teaching, scholarship, or research: 17 U.S.C. § 107. The analysis proceeds straight to the assessment of fairness, an assessment based on factors enumerated in the Code or established by the case law. Although one of those fairness factors includes whether the use is transformative, it is not at all clear that a transformative use is “absolutely necessary” for a finding of fair use: Campbell v. Acuff-Rose Music, Inc., 510 U.S. 569 (1994), at p. 579.