There is the doctrine of "fair use" which basically says small amounts of copying are ok when you use them to explain something about the work in question. Wha

There is the doctrine of "fair use" which basically says small amounts of copying are ok when you use them to explain something about the work in question. What is fair use is up to the courts. In a song if you copy part of the melody that really is the main thing and that really helps you sell your song, I don't think that's fair. Songs can not "explain" other melodies. So musical composition is a little different from text.