A pentachord in

music theory Music theory is the study of the practices and possibilities of music. ''The Oxford Companion to Music'' describes three interrelated uses of the term "music theory". The first is the " rudiments", that are needed to understand music notation (k ...

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

pitch class In music, a pitch class (p.c. or pc) is a set of all pitches that are a whole number of octaves apart; for example, the pitch class C consists of the Cs in all octaves. "The pitch class C stands for all possible Cs, in whatever octave positio ...

es, regarded as an unordered collection . In other contexts, a pentachord may be any consecutive five-note section of a

diatonic scale In music theory, a diatonic scale is any heptatonic scale that includes five whole steps (whole tones) and two half steps (semitones) in each octave, in which the two half steps are separated from each other by either two or three whole st ...

. A pentad is a five-note chord . Under the latter definition, a diatonic scale comprises five non-transpositionally equivalent pentachords rather than seven because the Ionian and Mixolydian pentachords and the Dorian and Aeolian pentachords are intervallically identical (CDEFG=GABCD; DEFGA=ABCDE). The name "pentachord" was also given to a

musical instrument A musical instrument is a device created or adapted to make musical sounds. In principle, any object that produces sound can be considered a musical instrument—it is through purpose that the object becomes a musical instrument. A person who pl ...

, now in disuse, built to the specifications of Sir Edward Walpole. It was demonstrated by

Karl Friedrich Abel Carl Friedrich Abel (22 December 1723 – 20 June 1787) was a German composer of the Classical era. He was a renowned player of the viola da gamba, and produced significant compositions for that instrument. Life Abel was born in Köthen, ...

at his first public concert in London, on 5 April 1759, when it was described as "newly invented" . In the dedication to Walpole of his cello sonatas op. 3, the cellist/composer

James Cervetto James Cervetto (8 January 1748 – 5 February 1837) was an English cellist, playing in aristocratic venues and in important concerts of the day. He was the soloist for the premiere of Haydn’s second cello concerto. Life Cervetto was born in Lo ...

praised the pentachord, declaring: "I know not a more fit Instrument to Accompany the Voice" . 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 The cello ( ; plural ''celli'' or ''cellos'') or violoncello ( ; ) is a bowed (sometimes plucked and occasionally hit) string instrument of the violin family. Its four strings are usually tuned in perfect fifths: from low to high, C2, G2, D ...

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