Question: No one may use a patent without the patent-holder's permission. But in a limited set of circumstances, others may use copyrighted material without the copyright-holder's permission. These circumstances-called the "fair use" exception-allow, for example, reviewers to quote from copyrighted material without permission, teachers to photocopy or distribute electronically and assign limited portions of copyrighted material to their classes, and musical groups to include or "sample" copyrighted music in their own compositions. Use economic theory to explain why it may be efficient to allow the fair use exception.