When the plaintiff has made a case of copyright infringement under US law, the defendant can still avoid liability by showing fair use. The defense comprises four factors, arguably the most important of which is the fourth, namely “the effect of the use upon the potential market for or value of the copyrighted work.” The word “potential” connotes a focus on the future, a need for courts to evaluate how events could unfold in days to come and what effect will thereby arise in that future world.