Fair use as related to copyright:
"Fair use" provisions may be interpreted as allowing quoting as much as a couple of paragraphs from a longer work or a few lines from shorter works such as poems WITH CLEAR CITATION.
There's no exact rule for all situations, but the point should be the honest, fair treatment of the copyright owner. As a rule of thumb, anything over 250 words exceeds "fair use". Most Bible versions permit longer quotes as long as the quote is no more than 50% of the total message.
written on October 2, 2003