Altered Chords
10 chords in this group
An altered chord is a dominant seventh with its fifth or ninth deliberately raised or lowered. The third and the seventh stay untouched, because those two notes are what make it a dominant at all — everything else is available for change, and changing it is how you make a chord pull harder.
What may be altered and what may not
The third and the minor seventh form a tritone, and that tritone is the engine. Take either away and the chord stops being a dominant. The fifth and the ninth carry no such duty, so both can move a semitone in either direction.
That gives four single alterations — ♭5, ♯5, ♭9, ♯9 — and their combinations. C7alt is the catch-all symbol meaning "use them", leaving the exact choice to the player.
One scale instead of a list
All four altered notes live in the altered scale, the seventh mode of melodic minor. From C that is C, D♭, D♯, E, G♭, A♭ and B♭ — every alteration and nothing else.
This is the practical way to think about the group. Rather than remembering which alteration goes with which chord, play one scale and let the voicing decide which of its notes appear on top.
Where they resolve
Usually into a minor tonic. A flat ninth and a flat thirteenth belong naturally to minor keys and sound sharply foreign in major ones, so C7alt leads to F minor far more comfortably than to F major.
The sharp ninth is the exception: blues and funk use it as a standing colour, not as tension. C7♯9 contains both a major and a minor third at once, and that contradiction is the sound rather than a problem to fix.
Voicings that fit under the hand
Drop the fifth and there is room for an alteration in the same number of notes. On guitar, C7♭9 is x32323, C7♯9 is x3234x, C7♭5 is x3435x, C7♯5 is x32314 — four shapes covering most of the group.
On the piano the standard approach is a shell: root in the left hand, third and seventh in the right, alterations above them. The fifth never appears, and nothing is missed.
The tritone substitution
Because a ♭5 chord is symmetrical, C7♭5 and G♭7♭5 contain the same four notes. One chord can therefore resolve into two different keys, and swapping a dominant for the one a tritone away is a standard reharmonisation.
It works because the tritone survives the swap while the bass moves down by a semitone — a motion the ear accepts without argument. Most altered chords in real arrangements arrive this way.
Frequently asked questions
What is an altered chord?
A dominant seventh with a raised or lowered fifth or ninth. The third and seventh stay unchanged.
What does C7alt mean exactly?
It names the approach rather than the notes: play a dominant with altered tones, chosen by the player from the altered scale.
Which scale fits altered chords?
The altered scale — the seventh mode of melodic minor. It contains every alteration and nothing else.