20:25:30:36

The major-minor seventh chord is a tetrad in 5-limit harmony, tuned 20:25:30:36 (1⁄1–5⁄4–3⁄2–9⁄5) and sometimes considered a form of dominant seventh chord. It combines a 5/4 major third with the consonant 9/5 seventh that would be found in a Ptolemaic minor seventh chord on the same root, creating a 36/25 tritone between the two.

The major-minor seventh chord is found rooted at 1⁄1 (I) and 4⁄3 (IV) in the duodene.

In septimal meantone, the 36/25 tritone is equated with the more consonant interval 10/7, and the major-minor seventh chord becomes an essentially tempered chord in the 9-odd-limit.