Added sixth chord

The term sixth chord refers to two different kinds of chord, the first in classical music and the second in modern popular music. The original meaning of the term is a chord in first inversion, in other words with its third in the bass and its root a sixth above it. This is how the term is still used in classical music today, and in this sense it is also called a chord of the sixth.

In modern popular music, a sixth chord is any triad with an added sixth above the root as a chord factor. This was traditionally (and in classical music is still today) called an added sixth chord or triad with added sixth since Jean-Philippe Rameau (sixte ajoutée) in the 18th century. It is not common to designate chord inversions in popular music, so there is no need for a term designating the first inversion of a chord, and so the term sixth chord can be used in popular music as a short way of saying added sixth chord. When not otherwise specified, it usually means a major triad with an added major sixth interval (a major sixth chord). However, a minor triad is also used, together with the same interval, resulting in a minor sixth chord (also known as minor major sixth).

In early music, what is today called a sixth chord or first inversion in classical music was considered an autonomous harmonic entity with the root named by the bass, while it was later simply considered an inversion of a chord with the bass being the third (not the root) and the root being the sixth (not the bass). In jazz, this form is referred to as a major sixth chord.

Alternatively, rather than as a six three chord, the note a may be analyzed as a suspension or appoggiatura, "first resolved and later...retained as a part of the chord, no resolution taking place.":

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