Shouldn't this thread be in the music section, above the line? :)

I believe that short segments of a literary work (including songs) can be "cited" in a scholarly or journalistic work, with proper author and copyright attribution, without permission or paying royalties. I'm just not sure about the specifics (e.g., how many lines, what portion of the work it can be).

I've actually researched this to some extent at a Stanford U. site concerning copyrights, but, as usual, the law is complicated and there's no quick and easy answer.