The purpose of parody in fair use copyright laws?

More recently, there’s the legal brouhaha of Sony vs. Beatallica. From Wikipedia:

Considering how much power the media industry holds over our current administration, I shudder to think what would’ve happened to our civil rights had this issue reached a federal courtroom…

Actually, IIRC, “Happy Birthday” is now in the public domain, is it not?

No, it’s not.

has the copyright on “Happy Birthday” expired yet?

Fair use also covers uses for educational purposes, criticism, political discussion, etc. I’ll go out on a limb and say this is probably not infringing.

This is a fascinating thread that I intend to read in its entirety when I’ve got the time. I’ve only skimmed it now, so forgive me if this has been covered (though I don’t think it has).

This comment inspired my question, which is this. Let’s say I copy a work, like a song, unchanged and completely, but I perform it in such a way as to parody it, would I be protected? I’m asking, essentially, if style or tone can convey parody, or just content?

Song performances are covered by what are called mechanical licenses. You always have the right to sing a song in any fashion you want, as long as you pay any necessary royalties given the situation.

Cecil covered it here.

What if I write different lyrics to an existing song, but not parody lyrics. I keep the exact music, just change the lyics. Can I do this if I give full credit for the music to the original author, or do I need to seek permission from them first before publishing my new song?