Dominant seventh chord
A dominant seventh chord is a tetrad comprising a root, a major third, a fifth, and a minor seventh.
The name of the chord derives from the dominant[1] scale degree, which is the only degree of a diatonic scale on which it is found. However, in many musical genres, “dominant seventh chord” informally refers to any chord with this general structure, regardless of where it appears in the overall scale.
JI Tunings
In the 3-limit:
- 576:729:864:1024, the Pythagorean dominant seventh chord, is found on the dominant scale degree (V or 3⁄2) of the Pythagorean diatonic scale.
In the 5-limit:
- 36:45:54:64, the Ptolemaic dominant seventh chord, is found on the dominant scale degree (V or 3⁄2) of Ptolemy's intense diatonic scale (Zarlino), perhaps the most common 5-limit diatonic.
- 20:25:30:36, the major-minor seventh chord, combines a major third with the consonant seventh that would be found in a Ptolemaic minor seventh chord built on the same root. It is found rooted at the I (1⁄1) and IV (4⁄3) of the duodene.
- 108:135:160:192 is found on the dominant scale degree (V or 3⁄2) of a diatonic scale with the second degree tuned a comma lower than in Zarlino (10/9 instead of 9/8), such as in left-handed nicetone.
- 128:160:192:225, an inversion of the Neapolitan[2] or German sixth[3] chord, is found rooted at the ♭II (16⁄15) and ♭VI (8⁄5) of the duodene. (Although 225/128 is often considered an augmented sixth rather than a minor seventh, in septimal meantone it is tuned identically to the harmonic seventh.)
In the 7-limit: