Chord
A chord is a collection of notes with well-defined pitches sounding together, or sometimes suggested in some manner, such as arpeggiation.
A chord's form is a description of its general structure, often using established categories (e.g. "major triad") or extensions thereof (e.g. "supermajor triad"), which summarize the intervals that constitute the chord. Most chord forms are named after the interval qualities of the intervals of the chord (e.g. "minor-major seventh chord"), while a few others are named after a harmonic function (e.g. "dominant seventh chord") or other composition techniques (e.g. "suspended second chord") when they are strongly associated. Chord forms do not provide precise tuning information, instead relying on interval regions to include a variety of similar chords.
A chord's function is a description of the context in which a chord is used, including how it relates to neighboring chords and to the scale upon which it is built (e.g. "Neapolitan" for a chord built on the ♭II degree of a scale).
Inversion
Chord inversion, or rotation
An inversion of a chord typically refers to a rotation of a chord, that is, a setting where one of the pitch classes is chosen as the lowest note. For example, a C major triad contains the tones C, E and G; its inversion is determined by which of these tones is the lowest note in the chord.
Melodic inversion
Melodic inversion, by contrast, describes literally inverting a chord, i.e. putting a chord upside-down. The two chords are inverses of each other. A chord whose inverse is itself is a palindromic chord, or palindrome. In negative harmony theory, chords are inverted with respect to the midpoint of the tonic and the fifth.
Chords by size
- Monad: 1 note
- Dyad: 2 notes
- Triad: 3 notes
- Tetrad: 4 notes
- Pentad: 5 notes
- Hexad: 6 notes
- Heptad: 7 notes