Critics of perpetual copyright also point out that creative activity often involves the creation of derivative works that recast or build upon previous material. If this prior material were perpetually copyrighted, their respective copyright holders would have the indefinite right to license their intellectual property or deny its use as they see fit. Many new derivative works could not be produced if the interested parties were denied permission or could not afford the licensing fees. Moreover, the longer copyright persists, the more copyrighted material falls into the category of orphan works. Anyone seeking to create derivative works based upon orphan works faces the risk of copyright infringement if the copyright holders were to come forward at some later time to enforce their rights. Perpetual copyright would create a significant disincentive to the creation of new literary or artistic works which build upon older material.