The Congress shall have Power … To promote the Progress of Science and useful Arts, by securing for limited Tımes to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.
This provision, from Article 1 Section 8 of the US Constitution, is a powerful tool that is designed to protect the creator's interests. However, this law is also designed to serve the public good. There is always this tension within the copyright law between the protection of copyright owners and exemptions designed for the public good.
The Fair Use Doctrine is one of those important exemptions. However, because this doctrine is ambiguous, there is often a tension in interpreting what exactly is "Fair Use." Therefore, each time you use a new work, or use a work in a new way, you need to apply these four factors:
- the purpose and character of your use
- the nature of the copyrighted work
- the amount and substantiality of the portion taken, and
- the effect of the use upon the potential market.
The links to the right do a fine job of defining these four factors.
