A pentachord in music theory

Music theory

Music theory is the study of how music works. It examines the language and notation of music. It seeks to identify patterns and structures in composers' techniques across or within genres, styles, or historical periods...

 may be either of two things. In pitch-class set theory, a pentachord is defined as any five pitch classes

Pitch class

In music, a pitch class is a set of all pitches that are a whole number of octaves apart, e.g., the pitch class C consists of the Cs in all octaves...

, regarded as an unordered collection (Roeder 2001). In other contexts, a pentachord may be any consecutive five-note section of a diatonic scale

Diatonic scale

In music theory, a diatonic scale is a seven note, octave-repeating musical scale comprising five whole steps and two half steps for each octave, in which the two half steps are separated from each other by either two or three whole steps...

 (Latham 2002). A pentad is a five note chord (Bailey 1991, 450).

Under the latter definition, a diatonic scale comprises five non-transpositionally

Transposition (music)

In music transposition refers to the process, or operation, of moving a collection of notes up or down in pitch by a constant interval.For example, one might transpose an entire piece of music into another key...

 equivalent pentachords rather than seven because the Ionian

Ionian mode

Ionian mode is the name assigned by Heinrich Glarean in 1547 to his new authentic mode on C , which uses the diatonic octave species from C to the C an octave higher, divided at G into a fourth species of perfect fifth plus a third species of perfect fourth : C D...

 and Mixolydian pentachords and the Dorian

Dorian mode

Due to historical confusion, Dorian mode or Doric mode can refer to three very different musical modes or diatonic scales, the Greek, the medieval, and the modern.- Greek Dorian mode :...

 and Aeolian

Aeolian mode

The Aeolian mode is a musical mode or, in modern usage, a diatonic scale called the natural minor scale.The word "Aeolian" in the music theory of ancient Greece was an alternative name for what Aristoxenus called the Low Lydian tonos , nine semitones...

 pentachords are intervallically identical (CDEFG=GABCD; DEFGA=ABCDE).

The name "pentachord" was also given to a musical instrument

Musical instrument

A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...

, now in disuse, built to the specifications of Sir Edward Walpole

Edward Walpole

Sir Edward Walpole KB PC was a British politician, and a younger son of Sir Robert Walpole, Prime Minister from 1721 to 1742....

. It was demonstrated by Karl Friedrich Abel

Karl Friedrich Abel

Carl Friedrich Abel was a German composer of the Classical era. He was a fine player of the viola da gamba, and composed important music for that instrument.-Life:Abel was born in Köthen, the son of Christian Ferdinand Abel, the principal viola da gamba and cello...

 at his first public concert in London, on 5 April 1759, when it was described as "newly invented" (Knape, Carters, and McVeigh 2001). In the dedication to Walpole of his cello sonatas op. 3, the cellist/composer James Cervetto praised the pentachord "than which I know not a more fit Instrument to Accompany the Voice" (Charters 1973, 1224). Performances on the instrument are documented as late as 1783, after which it seems to have fallen out of use. It appears to have been similar to a five-string violoncello (McLamore 2004, 84).