So let's say I like The Rover (Led Zep song), and I inadvertently (assume coincidence, no malice intent) take the chord progression and arrangement but change the melody and the lyrics so that the song becomes a brand new song. Is it really a brand new song, or a stolen idea? From what I've read on the interwebs the melody and lyrics are the key factor in determining infringement ... but then there is the example of Blurred Lines, where arrangement factored into the arguments ... I guess I am confused .... What makes a song a copyright infringement of another song? Assuming that my song is the one being copied, does a copyright even matter in this day and age? Or does it only "matter" if the new piece starts making money? How far does the copyright actually protect? Do I need a lawyer to review / validate my application (e.g. validity of claim, and Form SR or Form PA) before I submit it to copyright.gov? Is there a review board? If I do not copyright my original music, and assuming it is actually good and not just that I think its good, and I post it on Soundcloud (for instance) - am I in danger of having the song stolen outright? What protection do I actually have - with or without copyright? I'm especially interested in what the TGP members of the bar have to say, as well as what our singer songwriters are doing in practice. Thanks for all of your help with this guys. This is not academic (besides the first example) since I am at the stage myself.