Fair Use of Another's Copyrighted Work is Defined in Section 107 of the US Copyright Act (17 USC 101 - 810)

The United States Copyright Office provides some guidance regarding the fair use doctrine, as do other sites including Cornell University's LII - Wex and UCLA's Library. 

What is the Fair Use Doctrine?

In sum, it is a fair use of another's copyrighted work if you are using the work in order to provide criticism, in commentary, as part of news reporting, as part of teaching, in some form of scholarship, or in a research endeavor.

If there is litigation, courts are instructed to determine if the use is fair by applying a balancing test made up of several factors.  

Is Your Use a Fair Use?
The obvious place to start when considering whether or not your intended use of another's work comes within the fair use doctrine is to read the statutory definition itself.  According to the US Copyright Act, fair use is:

§ 107. Limitations on exclusive rights: Fair use


Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright.

In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include —
 (1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;

(2) the nature of the copyrighted work;


(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and

(4) the effect of the use upon the potential market for or value of the copyrighted work.


The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.

Two Things of Note After Reading the Fair Use Doctrine's Statutory Definition

1.  Notice that the statute does not give any set number of words that can be used before there is copyright infringement. There isn't one.

2.  Also, notice that if you give the hyperlink before the cut and paste of another's work, that's not addressed here. Attribution may help regarding a plagarism claim, but it's not going to be a solid defense against copyright infringement.

As lawyers and law firm write blogs and content for web sites, they may feel comfortable making their own legal call on whether or not their work falls within the fair use doctrine. Non-lawyers should seek legal guidance from an attorney to be on the safe side.