A report (No. 94-1476) from the The US House of Representatives goes into more detail by citing a 1961 report that highlights uses courts deemed to be fair:
quotation of excerpts in a review or criticism for purposes of illustration or comment;
quotation of short passages in a scholarly or technical work, for illustration or clarification of the author’s observations;
use in a parody of some of the content of the work parodied;
summary of an address or article, with brief quotations, in a news report;
reproduction by a library of a portion of a work to replace part of a damaged copy;
reproduction by a teacher or student of a small part of a work to illustrate a lesson;
reproduction of a work in legislative or judicial proceedings or reports;
incidental and fortuitous reproduction, in a newsreel or broadcast, of a work located in the scene of an event being reported.
The Four Factors
Figuring out what might be fair beyond the details
In addition to the above exceptions to copyright exclusivity, there are also four factors to consider when determining if a use benefits from the Fair Use Provision.
The purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes;
The nature of the work;
Amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
The effect of the use upon the potential market for or value of the copyrighted work.
Using the Four Factors
Ways to think about application
The Four Factors can be understood as weights on a balance scale, one side which favors fair use and the other which opposes. An analysis of the factors places a small or large weight in one pan or the other depending upon the determination. Once you consider all four factors, how balanced the scale is will help determine if the use favors fair use or not. (Read a case study: Can Arcadia University Use This Image for This Case Study?)
Is your use absolutely protected by the Fair Use Provision? There is no definitive answer. (Not that people haven’t tried, c.f., Building on Other’s Creative Expression) A reasonable evaluation of the Four Factors comes when you learn about them and understand how courts have ruled about them in cases.
Read Measuring Fair Use: The Four Factors at Stanford Copyright & Fair Use Center to learn in more depth about the Four Factors.
University of Minnesota Libraries' copyright website has a useful Fair Use Analysis Tool that will help you see how the four factors weigh with and against each other to help you decide what is fair use.
You may also get assistance from a copyright specialist or AU's Office of General Counsel.
Fair Use Guidelines
There are no bright lines between legal and illegal no matter what some might say.
Be aware that any guidelines you might use or read about are merely suggestions. US Copyright Law offers no quantities for assessing fair use. Guidelines may help you to think about amounts, but may severely limit your ability to use or reuse copyrighted works in reasonable ways that exceed the guidelines but still fall within the provisions of Fair Use.
In copyright, there are no true bright lines. Ultimately, only a court can determine if a use is fair. Statutory law can only say so much, then a judge must interpret through case law.