How much of someone else's work can I use without permission?
If you use a copyrighted work without authorization, the owner may be entitled to bring an infringement action against you. However, under the “fair use” doctrine, it is permissible to use limited portions of a work, including quotes, for purposes such as commentary, criticism, news reporting, and scholarly reports.
Whether a particular use qualifies as “fair use” depends on all the circumstances. There is no specific number of words, lines or notes, or percentages of a work that may safely be used or taken without permission. And, merely acknowledging the source of the copyrighted material does not substitute for obtaining permission.
In cases of doubt, the U.S. Copyright Office recommends you request permission from the copyright owner. Since the doctrine of “fair use” can be somewhat complicated, you may need to consult an attorney in order to fully understand if and how the “fair use” doctrine applies to you.