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9ths, 11ths, and 13ths
Builds on Seventh Chords
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Once a seventh chord is in place, you can keep stacking 3rds past the 7th: a 9th (an octave plus a 2nd above the root), an 11th (an octave plus a 4th), and a 13th (an octave plus a 6th). Each extension adds one more color tone without necessarily changing the chord's basic major/minor/dominant identity.
In practice, extended chords are rarely played with every note below the top extension intact — a voicing might quietly drop the 9th or 11th and jump straight to the 13th, since the ear mostly cares about the highest, most colorful extension present plus the defining 3rd and 7th. Extended chords are the backbone of jazz harmony's rich, layered sound.
⚠️ Common mistake
Assuming a 9th, 11th, or 13th chord must sound 'more dissonant' in proportion to how many notes it has. Extensions are chosen specifically because they add color without clashing — a dom9 or maj9 often sounds smoother than the plain 7th chord it's built from, not harsher.
📝 Summary
Extended chords keep stacking 3rds past the 7th: 9th, 11th, 13th. Each adds one color tone above the underlying 7th-chord quality, and jazz voicings often thin out the middle notes and keep just the top extension.
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