HarmoniYou're listening to Herbie Hancock play the dominant just before the return to the minor i. Four notes, one second long, and the whole piece seems to tip into a color you cannot reproduce. You lay down a clean G7, it works. You lay down the same G7 raising the 5th a half step, lowering the 9th, adding the #9 on top, and suddenly it bites. That is an altered chord at the piano. Not a mystery, not an exotic scale reserved for conservatories, just a dominant 7 whose tensions have been twisted a half step to prepare a more violent resolution.
This article takes the thing apart piece by piece. Theory, voicings, context of use, patterns to practice tonight. No academic tunnel.
What is an altered chord on the piano?
An altered chord is a dominant 7 whose tensions have been moved a half step. The root stays, the 3rd stays (the note that gives it its major character), the flat 7th stays (the note that screams "I am a dominant, I want to resolve"). Everything else moves.
On a normal G7 you have the perfect 5th (D) and three possible tensions: 9 (A), 11 usually avoided, 13 (E). On G7alt, those tensions become: b9 (Ab), #9 (A# or its enharmonic Bb), #11 (C#, which replaces the perfect 5th), b13 (Eb, which also acts as #5). Four altered tensions in one shot, and the perfect 5th disappears from the voicing.
The "alt" symbol on a lead sheet means exactly that: "play any alterations you want, your call." It is not one fixed chord, it is a family. A G7(b9) is altered. A G7(#9b13) too. A G7(#9#11) too. The term altered is an umbrella.
Where do the b9, #9, #11, b13 tensions come from?
All these notes come from a single scale: the altered scale, also called superlocrian. It is the seventh mode of the ascending melodic minor scale. Concretely, the G altered scale is the Ab melodic minor scale played starting from G.
Notes of the G altered scale: G, Ab, Bb, B, C#, Eb, F, G. Read it vertically and you land on the entire arsenal: root, b9, #9, major 3rd (the B, spelled here as an enharmonic of Cb but sounding as the 3rd of G7), #11, b13, b7. Nothing else. It is a scale designed for the altered dominant, full stop.
A shortcut, popularized by George Russell and then by the entire hard bop generation: to improvise over G7alt, play the melodic minor scale a half step above. Ab melodic minor over G7alt. B melodic minor over Bb7alt. It is mechanical, it works everywhere, and it spares you from thinking in altered mode during a chorus at 240 to the quarter note.
How to voice an altered chord without it sounding sloppy
The classic trap: stacking the four altered tensions at once, plus the 3rd, plus the 7th, and getting a mush of half steps that no longer sounds like a dominant but like an experimental organist's cluster. Pro pianists select. Always.
The rule that saves you: 3rd and 7th on the bottom (the guide tones), one or two alterations on top. Never more. The typical rootless voicing on G7alt in the right hand looks like this: B (3rd) - F (b7) - Ab (b9) - Eb (b13). Four notes, spread intervals, no needless dissonance. If you want the #9 instead of the b9, replace Ab with Bb. If you want the #11 rather than the b13, replace Eb with C#.
| Target chord | Right-hand voicing | Active tensions |
|---|---|---|
| G7(b9) | B - F - Ab - E | b9, 13 |
| G7(#9) | B - F - Bb - E | #9, 13 |
| G7(b9#11) | B - F - Ab - C# | b9, #11 |
| Full G7alt | B - F - Ab - Eb | b9, b13 |
| G7(#9#11) | B - F - Bb - C# | #9, #11 |
The root G? To the bass player, or to your left hand walking if you play in a trio without an upright. The rootless voicing does not need the root to function, that is precisely the point. To dig into this technique, read our dedicated article on rootless voicings at the piano.
When do you place an altered chord in a progression?
Three contexts where the altered chord falls naturally, and one context where you should abstain.
On the dominant of a minor ii-V-i
Almost automatic. On a Dm7(b5) - G7alt - Cm, the G7alt is so expected that playing a clean G7 sounds bland. The b9 of G (Ab) prepares the flat 5th of the Dm7(b5) that preceded it, the b13 (Eb) already announces the minor third of the target Cm. Direct voice leading, an almost automatic resolution. To review the mechanics of the ii-V-i, see ii-V-I jazz piano.
On the dominant of a major ii-V-I when you want to bite
Optional but rewarding. A G7alt resolving to Cmaj7 creates a strong contrast: you go from a chord saturated with tension to a luminous chord. The device is all over Bill Evans, notably on Sunday at the Village Vanguard in 1961. Use it in moderation. Three G7alt in a row in a blues chorus is heavy.
On a secondary dominant aiming at a minor chord
If your progression contains a V7/vi (an E7 in the key of C major, resolving to Am), turning that E7 into E7alt sounds better than leaving it plain. The rule of thumb: a dominant that resolves to minor is a natural candidate for alteration.
When to abstain
On a dominant that does not resolve. On a minor blues dominant played in an open bluesy mode (the natural 9 sounds better). On a dominant with a melody that sings the natural 13 or the natural 9 in the right hand: altering underneath creates a head-on dissonance you did not intend. Always look at the melody before deciding.
Three altered-chord patterns to practice tonight
Theory without the fingers is just reading. Here are three short exercises that get the altered sound into your ear in a single session.
Pattern 1: minor ii-V-i in a loop, all twelve keys. Slow tempo, metronome at 60. Dm7(b5) - G7alt - Cm6, then move up a half step: Ebm7(b5) - Ab7alt - Dbm6. You go through all twelve keys. Fifteen minutes a day, every day, two weeks. The G7alt voicing ends up coming out on its own under the fingers.
Pattern 2: alternate b9 and #9 on the same dominant. Play Cmaj7 - G7(b9) - Cmaj7 - G7(#9) - Cmaj7. Listen to the difference in color between b9 (slightly sad, Spanish) and #9 (bluesy, electric, it is Hendrix's chord on Purple Haze). Your ear automatically sorts which one you want depending on the melodic context.
Pattern 3: tritone substitution and altered chord are linked. Play G7(b9b13). Now play Db7(9#11). They are almost the same notes. The root changes, the tensions swap, but the B - F tritone is shared. Understanding this unlocks tritone substitution at the piano and explains why the two tools sound so close.
How HarmoniKeys helps you integrate altered chords
The main block on altered chords is not the theory, it is visualization. You know that G7(b9#11) contains G, B, F, Ab, C#. But at a medium tempo, your fingers are still hunting. HarmoniKeys shows the voicing in color directly on the keyboard, plays you the sound, and has you chain onto the resolution chord to hear how the tension releases. Visual memory and aural memory build in parallel, without a theory detour on every repetition.
Practice altered voicings at the keyboard
Open HarmoniKeys, choose the minor ii-V-i progression, turn on the altered dominant option, and loop it through twelve keys.
Open HarmoniKeysGoing further
The altered chord is only one tool among those that turn an ordinary dominant into a high point of the piece. Its natural counterpart is the tritone substitution, which often reaches the same sound by a different road. Its rhythmic counterpart is the voice leading between the altered dominant and the target chord: without clean voice leading, the altered tension does not resolve, it collapses. Work the three together. That is where the sound really changes.