2. Copyright Basics: Why it exists
U.S. Copyright Law has its origin in the U.S. Constitution:
“The Congress shall have the power … to promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors exclusive Right to their respective Writings and Discoveries.” - U.S. Constitution Article 1, Section 8
In other words: The U.S. Congress has the power to create laws that govern copyright.
The purpose of copyright is to encourage the creation and sharing of creative works. Copyright gives a creator the incentive to share their work by providing a limited monopoly so that the creator can profit from his or her creation. Congress determines the limits of this monopoly, including the length of time that copyright coverage lasts. These limits can, and have, changed over time.