You famously only need four chords to play everything, or maybe it's only three. But how true is this really? I decided to go look and see what was common. I looked at a large number of transcribed songs, writing down which chords were used. This isn't perfect: some chords are more optional than others, but it's about right. I only wrote down the triad: C7 and Cmaj7 are just C. I used three sour