1
Why 13th Chords
As the background to my music theory is more classical in nature, it used to puzzle me when I saw jazz chords like C9, B♭11 or F13. I mean, I knew what a 9th, 11th and 13th note were but I wondered why you'd call a note a 9th rather than a 2nd, or a 13th rather than a 6th and so on.