In the Constitution, copyright was included as a way to protect people from theft and influence them to promote creativity and enlightenment as the country progressed. At the beginning, copyright was not a restricted right. But as more and more people started creating their own pieces of work, copyright became more and more restricted. This was influenced by Thomas Jefferson, who believed copyright could bring creativity to the United States. There have been several shifts in how copyrighted work is used. For example, if an author has been dead for more than 70 years, then work could be used with special permission from a person or source. Most works, including some outside the United States, have this special privilege. However, some big name authors who have been dead for more than 70 years, follow the same basic rules as those who have been dead for less than 70 years. Overall, copyright is a basic way to protect the people who have created works from theft and allow the people to boost their own creativity and uniqueness, as Thomas Jefferson proposed when the Constitution was created.
For more info on copyright: please see this two sources:
http://copyright.cornell.edu/resources/publicdomain.cfm
http://chnm.gmu.edu/digitalhistory/copyright/1.php
http://elastico.net/copyfight/upload/siva_jefferson.pdf
