Here are two excerpts that I think are informative. [Note
that they both are products of the U. S. Government and thus
in the public domain!]
"Copyright protects the particular way authors have expressed
themselves. It does not extend to any ideas, systems, or factual
information conveyed in a work."
— http://www.copyright.gov/fls/fl102.html
I think this is illuminating because it says something concise
and authoritative about what cannot be copyrighted. The next
quotation is from a a leagal ruling, and I think
it sheds some light on Fair Use and its limits.
"[A] reviewer may fairly cite largely from the original work,
if his design be really and truly to use the passages for
the purposes of fair and reasonable criticism. On the other
hand, it is as clear, that if he thus cites the most
important parts of the work, with a view, not to criticize,
but to supersede the use of the original work, and
substitute the review for it, such a use will be deemed in
law a piracy ... "
— Judge in Joseph Story in Folsom v. Marsh
(see http://en.wikipedia.org/wiki/Fair_use)