The term "four-part harmony" refers to music written for four voices, or four musical instruments, where the various parts give a different note of each chord of the music. Typically, the first of the four parts will sing (or play) the melody, with the other three parts providing the supporting harmonies. It is unusual for any of the four parts to share the same note, although it happens at times.
Four parts for voices
In choral music, the four main voices are typically labelled as: soprano (or treble), alto (contralto or countertenor), tenor, and bass. Because most singers have a relatively limited range, the upper notes of the soprano or tenor part cannot be sung by a bass singer. Conversely, the lower notes of the bass part typically cannot be reached by a soprano voice, with some notes so low that alto and tenor voices cannot reach them either.
Groups of just four people, singing as quartets, can perform in four-part harmony. A special genre in this music is the "barbershop quartet" usually consisting of four men or women who sing tenor, countertenor, baritone, and bass parts. A barbershop quartet typically sings with extra focus on emphasizing, or exaggerating, the harmonies in a piece of music, rather than singing in quiet supporting roles to a louder, solo melody voice. All four voices often sing with such intensity that it is difficult to mimic the sound from just hearing the melody part separately, where the supporting voices can provide counterpoint melodies, close harmonies, or a walking bass to the melody line.
Four parts for instruments
Some music is written, in four-part harmony, for small groups of only four instruments, such as a string quartet, a brass quartet, or a woodwind quartet. Each instrument could be scored to mimic the four voices of choral music. However, due to the range of musical instruments covering more pitches than a typical human voice, a quartet might play some harmonies with very high notes or very low notes, rather than the blended range of choral music.
Beyond quartets, in large orchestras or musical bands, the larger sections of instruments, such as violins, cellos, clarinets, flutes, trumpets, or French horns often have music written in four-part harmony. Similar to vocal music, the first part for a section of instruments typically plays the melody line, in some passages of a composition, with the other parts playing the supporting harmonies. The third part is often a harmonic mirror of the first part, which will sound somewhat melodic as well (if played separately). However, the second and fourth parts usually play close harmonies, in a more monotonous range, and rarely sound as melodic as the third part. Because musical instruments typically have a wider range than a human voice, any instrument in each section of a band or orchestra is able to play any of the four parts, although the first part often has high notes, or faster notes, that only a more experienced musician can play well.
- Benward & Saker (2003). Music: In Theory and Practice, Vol. I, p.159. Seventh Edition. ISBN 978-0-07-294262-0.
- McKinney, James (1994). The Diagnosis and Correction of Vocal Faults. Genovex Music Group. ISBN 978-1-56593-940-0.
- Boldrey, Richard (1994). Guide to Operatic Roles and Arias. Caldwell Publishing Company. ISBN 978-1-877761-64-5.