On appeal, UMG also contends that the district court failed to give the jury an adequate instruction on “fair use,” an affirmative defense that it raised at trial. The doctrine of fair use operates to prevent the mechanistic enforcement of copyright law in a way that would work to repress creativity. It constitutes an affirmative defense that may be raised when there is substantial similarity between two works and evidence of copying. Under the federal copyright statute, fair use covers purposes such as “criticism, comment, news reporting, teaching ․, scholarship, or research.” 17 U.S.C. § 107. In determining applicability of the doctrine of fair use, courts consider these statutory factors: