Section 31.3 Altered Dominant Seventh Chords
Typically, a dominant seventh chord is considered altered if either or both the 5th or 9th are chromatically raised or lowered. (“G7alt” might mean a G7 with both an altered 5th and 9th, but is vague in that it doesn’t specify how the 5th and 9th are chromatically altered.)
- Root, 3rd, and 7th of dominant seventh chord remain unchanged.
- 5th may be raised or lowered (♯5 or ♭5, which can also be written with pluses and minuses as \(\left.\text{}{+}\right.\)5 or –5) and can be respelled enharmonically (the ♯5 of a C7♯5 could be written as an A♭ instead of G♯) for ease of reading because the chromatic spelling agrees with B♭ (the 7th of the chord)—it is easier to read a chord where the accidentals agree (all sharps or all flats).
- 9th may be raised or lowered (♯9 or ♭9, which can also be written in the lead-sheet symbol as +9 or –9). The ♯9 is often spelled enharmonically on the staff as ♭10 for ease of reading; therefore, a dominant seventh chord with a ♯9 will appear to have both a major and minor 3rd (C–E–G–B♭–E♭). You may be tempted to call such a chord a minor chord with a ♭11, but ♭11 is not used because it is the major third of a chord.
- Both alterations of 5 and 9 may occur simultaneously (±9/±5).
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♭13 is the enharmonic equivalent of the ♯5. In this text, ♯5 is preferred to ♭13, but you will see both on lead sheets. Also, ♭13 implies that the unaltered 5th occurs in the chord, while ♯5 does not.
If you are composing or arranging and want to know when to use altered chords, know that dominant sevenths are usually altered (with altered 5th or 9th or both) when they have dominant function (i.e., when the root is going to resolve down by a fifth). Dominant sevenths are often unaltered when they have tonic function, i.e., the first chord in a blues.
