Harmony and Chord Extensions
Like Duolingo, but for Harmony and Chord Extensions. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
For the part of you with thirty open tabs that never became anything.
Free during early access · No credit card · iPhone & Android
Key ideas in Harmony and Chord Extensions
- The 'add' label tells you to skip the 7th degree entirely
- The 9th adds color and texture without creating harmonic instability
- A standard C9 chord automatically includes the flat 7th
- Unlike the 7th, the 9th doesn't force the chord to resolve to a new key
- Adding a 9th without a 7th keeps the chord's basic structure intact
- Add9 chords maintain the functional 'rest' of a standard major triad
- The structural difference between an 'add' chord and a standard extension
- The functional impact of adding a 9th versus a 7th
- The 9th is the same pitch as the 2nd but voiced an octave up
- Spacing the 9th away from the root prevents 'muddy' frequency clashes
- Harmonic clarity comes from the wide interval between the root and the 9th
- The voicing and interval relationship of the 9th
- C9 contains a tritone between the 3rd and the flat 7th
- C add9 removes the 'bluesy' bite associated with dominant 7th chords
- The absence of the 7th eliminates the dissonant rub against the 3rd
- The sonic character difference between C add9 and C9
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives Harmony and Chord Extensions the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
If you are playing a 'C add9' chord, what specific note should you leave out of your hand?
Get it right to open this lesson and 69 more in the app.
Where Harmony and Chord Extensions takes you
Move beyond basic triads to master the sophisticated world of chord extensions, from the subtle shimmer of 'add' chords to the functional tension of dominant 9ths and 13ths.
- 1
The 'Add' vs. '7th' Distinction
- The 'Add' Rule for Immediate Color
- The Dominant 9th and Functional Tension
- 2
The Logic of the Tertian Stack
- Stacking Thirds Beyond the Octave
- Compound Intervals and Harmonic Spacing
- 3
The 7th as the Gatekeeper
- Major 7th vs. Dominant 7th Extensions
- Minor 9th and Minor 'Add' Chords
- 4
Advanced Extensions: 11ths and 13ths
- The 11th and the 'Avoid Note' Problem
- The 13th: The Ultimate Extension
- 5
Altered States and Spicy Harmony
- The Flat 9 and Sharp 9
- The Lydian #11 and Acoustic Scale
- 6
Voice Leading with Extensions
- Smooth Voice Leading for 9ths
- Shell Voicings and Extension Economy
- 7
Functional Substitution
- Replacing Triads with Extended Chords
- The 'Sus' Extension Hybrid
- 8
Modern and Polychordal Concepts
- Upper Structure Triads
- Quartal Extensions
- 9
The Physics of Why it Works
- The Overtone Series and Extensions
- Psychoacoustics of Harmonic Density
9 sections · 18 units · 70 levels. Built to play, not to enroll.
You pick the voice
Harmony and Chord Extensions is taught in the Explain Like I'm 5 style: no big words. promise.. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
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