A Dictionary of Music and Musicians/Chorus
CHORUS. 1. The body of singers at an opera, oratorio, or concert, by whom the choruses are sung.
2. Compositions intended to be sung by a considerable body of voices—not like glees, which are written for a single voice to each part, or like part-songs, which may be sung indifferently by single voices or larger numbers. Choruses may be written for any number of parts, from unison (Bach, No. 5, in 'Ein' feste Burg'; Mendelssohn, parts of No. 7 in 'Lauda Sion') and two parts (Haydn, Credo of Mass No. 3; Mendelssohn, No. 2 of 95th Psalm) to 40 or 50; but the common number is from 4 to 8. Handel mostly writes for 4, though occasionally, as in 'Acis and Galatea,' for 5, and, in 'Israel in Egypt,' for 8, divided into two choirs. In the latter days of the Italian school, Gabrielli, Pitoni, etc., wrote masses and motets for as many as 10 and 12 choirs of 4 voices each. Tallis left a chorus in 40 independent parts, called his '40-part song.' Choruses for 2 choirs are called double choruses; those in Handel's 'Israel in Egypt' and Bach's 'Matthew Passion' are the finest in the world. The two choirs answer one another, and the effect is quite different from that of 8 real parts, such as Palestrina's 'Confitebor,' 'Laudate,' or 'Domine in virtute' (see De Witt's ed. ii. 132, etc.), Gibbons's 'O clap your hands,' or Mendelssohn's 'When Israel out of Egypt came.' Handel often begins with massive chords and plain harmony, and then goes off into fugal treatment. In the 'Darkness' chorus in 'Israel,' he introduces choral recitative; and Mendelssohn does something similar in the chorus in 'St. Paul,' 'Far be it from thy path.' In his 'Kirchen Cantaten' Bach's choruses are often grounded on a chorale worked among all the parts, or sung by one of them, with independent imitative counterpoint in the rest. But for these varieties see the article Form.
In the opera the chorus has existed from the first, as is natural from the fact that opera began by an attempt to imitate the form of Greek plays, in which the chorus filled an all-important part. Till Gluck's time the chorus was ranged in two rows, and however stirring the words or music they betrayed no emotion. It was he who made them mix in the action of the piece. In modern operas the choruses are absolutely realistic, and represent the peasants, prisoners, fishermen, etc., who form part of the dramatis personæ of the play.
[App. p.591 adds that "the word was very commonly used, in the 17th and 18th centuries, to denote the concerted conclusion of duets, trios, etc., and was in fact the exact equivalent of our 'ensemble.' The meaning of the word has frequently been misunderstood, as for in many modern editions of Purcell's well-known duet 'Hark, my Daridcar!' where the last ensemble section, beginning 'So ready and quick is a spirit of air' has been omitted, no doubt under the impression that the word 'Chorus' meant that these bars were to be sung by many voices. Conclusive proof that the word was used commonly in this sense is afforded in many of Handel's Italian operas, in the scores of which the names of the quartet of soloists are placed at the beginning of their respective lines in ensemble numbers, though the movement is entitled 'Coro.'"]