Seventh chord

In its earliest usage, the seventh was introduced solely as an embellishing or nonchord tone.

The seventh destabilized the triad, and allowed the composer to emphasize movement in a given direction.

Additionally, the general acceptance of equal temperament during the 19th century reduced the dissonance of some earlier forms of sevenths.

It is denoted using popular music symbols by adding a superscript "7" after the letter designating the chord root.

An often heard example of the harmonic seventh chord is the last word of the modern addition to the song "Happy Birthday to You", with the lyrics, "and many more!"

The harmony on the word "more" is typically sung as a harmonic seventh chord.

As pianos, and other equal-temperament instruments cannot play this chord, it is frequently approximated by a dominant seventh.

As a result, it is often called a dominant seventh chord and written with the same symbols (such as the blues progression I7–V7–IV7).

While the dominant seventh chord is typically built on the fifth (or dominant) degree of a major scale, the minor seventh chord is built on the second, third, or sixth degree.

The major seventh is sometimes notated as Δ7 (a delta chord) or just a Δ (which has the same meaning).

The diminished seventh chord has been used by composers and musicians for a variety of reasons over time.

Some reasons include: as a symbol of Sturm und Drang; modulation; and for characterisation.