Stated simply, copyright law protects author by forbidding others to copy his or her original work for a limited period of time (generally for the life of the author, plus fifty years. 17 U.S.C. § 302). However, a key question is what constitutes"original work." (for example, reciting mere historical facts is not "original.")
In addition, certain exceptions exist to this general rule. For example, the Fair Use doctrine creates exceptions for educational uses of original works, for example a professor's use of excerpts in a classroom, or this site's use of excerpts of book and movie reviews.
With respect to literature, copyright is not extended merely to the
words of a text; if this were so, plagiarists could steal characters, plots,
and settings merely by changing a word or two of the original text. Instead,
courts inquire as to the part taken from the original -- be it a character,
plot, literal text, or other aspect -- is "substantial." Because
"plagiarism" is not a recognized cause of action by itself, it is usually
pled as claims for copyright infringement, breach of contract, breach
of confidence, fraud, negligent misrepresentation, unfair competition,
ar misrepresentation. Combined in a single complaint they create quite
a procedural puzzle because copyright infringement is a claim over
which federal courts have exclusive jurisdiction, while the other claims
are state law claims over which state courts have jurisdiction.