Copyright law, which promotes the creation of cultural and artistic works by protecting these works from being copied, excuses infringement that is deemed to be a fair use. Whether an otherwise infringing work is a fair use is determined by courts weighing at least four factors, one of which is the effect of the otherwise infringing work on the market for the copyrighted work. The Supreme Court’s decision just over twenty years ago in Campbell v. Acuff-Rose Music, Inc., opened the door to a laudable analytical framework for the bearing of market effects on fair use. First, Campbell supports a more full-bodied investigation of the market effects — both harms and benefits — of defendants’ works on plaintiffs’ copyrighted works. Courts can eliminate conclusory reasoning by appreciating that both market harms and benefits can matter in assessing fair use. In so doing, courts avoid weighing only the mere possibility that a licensing market does or could exist for a copyrighted work as a reflection of market harm and ignoring the possibility that a use of a copyrighted work might confer benefits on the copyright holder. Second, Campbell implied two important ways to divide relevant from irrelevant market effects. One ought to exclude market effects from consideration if they are empirically unlikely or if there are effects unrelated to the protectable aspects of the copyrighted work, such as its ideas or the societal value attributed to the work. This analytical framework for market effects bearing on fair use advances copyright’s goal of promoting the creation of artistic and cultural works from which society can benefit.