For example, in Fox Film v. Doyal , the court said, The sole interest of the United States and the primary object in conferring the [copyright] monopoly lie in the general benefits derived by the public from the labors of authors. This fundamental decision explains why copyright is not required by the Constitution, only permitted as an option -- and why it is supposed to last for "limited times." If copyright were a natural right, something that authors have because they deserve it, nothing could justify terminating this right after a certain period of time, any more than everyone's house should become public property after a certain lapse of time from its construction. The "copyright bargain" The copyright system works by providing privileges and thus benefits to publishers and authors; but it does not do this for their sake. Rather, it does this to modify their behavior: to provide an incentive for authors to write more and publish more. In effect, the government spends the public's natural rights, on the public's behalf, as part of a deal to bring the public more published works. Legal scholars call this concept the "copyright bargain." It is like a government purchase of a highway or an airplane using taxpayers' money, except that the government spends our freedom instead of our money. But is the bargain as it exists actually a good deal for the public? Many alternative bargains are possible; which one is best? Every issue of copyright policy is part of this