quick copyright question....?

[look-closer.livejournal.com]

lately i've been doing a lot of mixed media collaging, and generally, if i want words, i use my own (being that i am a freelance writer) but i thought i should ask... is it a violation of copyright if i use, say, a quote from a book or song in a piece of art and then sell it?

logically, it seems like it would be, but i thought i'd check. thanks!