I remember learning the theory of using these extended chords by studying compositions to see how they were used. I already knew the sound, so I learned to associate the sound with the notation. Of course, this was fifty years ago so I'm a bit hazy.

The 13 to me is the big brother of the 9th, not the little brother by any means, because the 13 chord includes the 9. I love dominant 13 chords that contain both the sixth and dominant sevenths: so many choices!

When you are studying #4, I suggest you look for #11 instead. You'll find that more frequently. And of course a #4 and b5 are enharmonically the same note; the b5 is far more common.


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