Is fair use a question of law or a question of fact?

“[W]here the case is tried on stipulated facts, or both sides cross-move for summary judgment, there is no reason why the court may not decide the issue as a matter of law; indeed, fair use is frequently decided on summary judgment. On rare occasions, courts have decided fair use on a rule 12(b)(6) motion to dismiss for failure to state a claim. 4 Patry on Copyright § 10:159 (citations omitted; emphasis added).