Minor Seventh

In classical music from Western culture, a seventh is a musical interval encompassing seven staff positions (see Interval number for more details), and the minor seventh is one of two commonly occurring sevenths. It is qualified as minor because it is the smaller of the two: the minor seventh spans ten semitones, the major seventh eleven. For example, the interval from A to G is a minor seventh, as the note G lies ten semitones above A, and there are seven staff positions from A to G. Diminished and augmented sevenths span the same number of staff positions, but consist of a different number of semitones (nine and twelve).

Minor seventh intervals are rarely featured in melodies (and especially in their openings) but occur more often than major sevenths. The best-known example, in part due to its frequent use in theory classes, is found between the first two words of the phrase "There's a place for us" in the song "Somewhere" in West Side Story. Another well-known exception occurs between the first two notes of the introduction to the main theme music from Star Trek: The Original Series theme.

The most common occurrence of the minor seventh is built on the root of the prevailing key's dominant triad, producing the all-important dominant seventh chord.

Harry Partch distinguishes between the 16:9 "small just 'minor seventh'" and the 9:5 "large just 'minor seventh'". A minor seventh in just intonation, also known as Pythagorean small minor seventh, typically corresponds to a pitch ratio of 16:9 (Pythagorean small minor seventh Play) or 9:5 Play (5-limit large minor seventh), while in an equal tempered tuning it is a ratio of 25/6:1 (about 1.782), or 1000 cents, 3.91 cents wider than the 16:9 ratio and 17.60 cents narrower than the 9:5 ratio. The 9:5 greater just minor seventh arises in the C major scale between E and E and A and G. The 16:9 lesser minor seventh arises in the C major scale between G & F, B & A, and D & C.

An interval close in frequency is the harmonic seventh, or septimal minor seventh, with an exact 7:4 ratio (i.e., 1.75), which makes it quasi-harmonically significant. This interval is about 969 cents, or one-third of a semitone flatter than the equal-temperament minor seventh (1000 cents).

Consonance and dissonance are relative, depending on context, the minor seventh being defined as a dissonance requiring resolution to a consonance