Fair use allows you to use copyrighted works without permission for a limited and transformative purpose, such as commentary, criticism, news reporting, teaching, scholarship, research, or parody. Fair use exception to copyright is not as defined as other exceptions, such as classroom or library uses. Only court cases provide definitive exceptions.
17 U.S. Code § 107 spells out four factors to determine if a use is fair. You must weight each of these factors, no single factor is decisive. The ALA's fair use analysis tool will assist you with weighing the factors and will email you your choices so you'll have a record.
Nonprofit, education uses of a work are generally favored over commercial uses. The transformative uses listed above are frequently employed at Virginia Tech. Including quotations in a paper, using small parts of a work in a teaching presentation, or using sections of a work as a part of a commentary or criticisms are more likely to be considered fair use.
Not all nonprofit, education uses would be considered fair. All four factors must be considered.
Factual or nonfiction works or published works lend themselves to fair use over creative works (fiction, poetry, music, film, works of art) or unpublished works (personal correspondence or manuscripts).
Works produced specifically for education markets, like workbooks or case studies, would not favor fair use.
While copyright law does not set exact limits, generally the more of a work you use, the less likely you are within fair use. Consider the amount you want to use against the length of the entire work. Even a small portion of a work may be considered the heart of the work and not fair use.
This factor includes both actual markets and potential markets; just because a work is not currently available for sale does not mean the potential to profit from the work isn't there.