Altered Diminished

It is not the altered scale — and the names collide badly

Search demand for this scale is almost entirely demand for a different one. The phrase people type is «altered dominant scale», and that is the altered scale, the seventh mode of melodic minor, spelled 1 ♭2 ♭3 ♭4 ♭5 ♭6 ♭7. This one has a double-flatted seventh instead, which changes the chord it belongs to.

The difference is one note and it is decisive. With a ♭7 the scale contains a dominant seventh chord and is used over altered dominants — G7♯5♯9 and its relatives. With a ♭♭7 — enharmonically a sixth — the scale contains a diminished seventh chord instead, and it belongs over that.

Because the two names are almost identical and one of them is far more common, most pages found by searching «altered» describe the melodic minor scale. If you arrived here expecting that one, it is catalogued separately under the altered scale.

Where it comes from and what it fits

Build a seven-note scale on the seventh degree of harmonic minor and this is the result. In A harmonic minor the seventh degree is G♯, and the chord standing there is G♯ diminished seventh — the chord classical harmony uses as a substitute for the dominant, because it shares three of its four notes.

The scale therefore has a narrow, specific job: it supplies the notes available while that diminished chord sounds. Every note of G♯ dim7 is in it, plus the passing tones that the parent key provides, which is exactly what a soloist needs over a chord that would otherwise offer only four pitches.

In practice most players never name it. They play A harmonic minor over the G♯ dim7 chord, which produces the same notes; the name matters when you are analysing what you played rather than when you are playing it.

How to read the double flat

The ♭♭7 looks like a notational curiosity and it is not. Spelling matters here because the scale is defined as a rotation: each degree of harmonic minor must keep its letter name, so the seventh degree of a scale built on G♯ has to be some kind of F. Written as F, it is a ♭♭7; written as E, the arithmetic of the mode breaks.

On an instrument the distinction disappears — F♭♭ and E are the same key, the same fret. The reason to keep the spelling is that it tells you which chord the note belongs to. Called a ♭♭7 it is the seventh of a diminished chord; called a sixth it is a colour on something else entirely.

This is the same principle that governs ♯5 against ♭13 elsewhere in the catalogue: the sound is identical, the function is not, and the notation records the function.

Frequently asked questions