A chord progression, is the harmonic function of the song. It is the chords used in a song, and the order they are used. Its not just the one that is uncopyrightable, No chord progression can have a copyright. Many are used over and over again. The harmony while important is not what identifies a song. Its the melody and the lyrics. If you have ever heard a twelve bar blues its the some chord progression, and about 10 million different songs .Same with the so called Axis progression, also known as the “Let it Be” progression. They key is not relevant either. There are quite a few other very familiar chord progressions (to musicians anyway). You can copyright individual notes either. In other words you cant own Bb. You also cant own the title. Which is why many songs have the same title.
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