A number in music is a self-contained piece that is combined with other such pieces in a performance. In a concert of popular music, for example, the individual songs or pieces performed are often referred to as "numbers." The term is applied also to sections of large vocal works (such as opera, oratorio, or musical) when the written or printed score for such a work designates the titles of the pieces with sequential numbers, hence the aptness of the term. The use of numerical designations in extended vocal musical works has the practical advantage of facilitating rehearsal plans, especially when their designations include assignment of characters.
The number opera (Italian: opera a numeri; German: Nummeroper) is an opera consisting of individual pieces of music ("numbers") which can be easily extracted from the larger work.[1] They are often numbered consecutively in the score and may be interspersed with recitative or spoken dialog. The numbers primarily consist of arias but also occasionally ensemble pieces, such as duets, trios, quartets, quintets, sextets or choruses and may also include ballets and instrumental pieces, such as marches, sinfonias, or intermezzi.[2] Number operas were common up until the early 19th century and included opera seria, opera buffa, opéra comique, ballad opera, Singspiel, and some grand operas.[1]
The replacement of numbers with more continuous music began with operas by Jommelli, Traetta, Gluck, and especially Mozart, whose late operas Le Nozze di Figaro and Don Giovanni contain several segments in which different numbers are unified by bridge passages to form a musical whole. This trend became even more striking in the operas of the German composers Beethoven, Weber, and Meyerbeer, while their Italian and French contemporaries Rossini, Donizetti, Bellini, and Auber retained the number-opera style.[2]
The number opera was strongly condemned by Wagner for dramatic reasons, and he replaced it with continuous music that follows the drama without interruption.[2] The number opera became unfashionable, and the late operas of Verdi and those of Puccini and the verismo school, cannot be described as such.[1] In fact, almost all operatic composers subsequent to Wagner adopted this procedure.[2] However, in the 20th century some composers intentionally revived the number opera style, e. g., Busoni's Arlecchino (1917),[3][4] Berg's Wozzeck (1925),[1] Hindemith's Cardillac (1926, rev. 1952), and Stravinsky's The Rake's Progress (1951).[2]