ACCOMPANIMENT (i.e. that which "accompanies"), a musical term for that part of a vocal or instrumental composition added to support and heighten the principal vocal or instrumental part; either by means of other vocal parts, single instruments or the orchestra. The accompaniment may be obbligato or ad libitum, according as it forms an essential part of the composition or not. The term obbligato or obbligato accompaniment is also used for an independent instrumental solo accompanying a vocal piece. Owing to the early custom of only writing the accompaniment in outline, by means of a "figured bass," to be filled in by the performer, and to the changes in the number, quality and types of the instruments of the orchestra, "additional" accompaniments have been written for the works of the older masters; such are Mozart's "additional" accompaniments to Handel's Messiah or those to many of the elder Bach's works by Robert Franz. In common parlance any support given, e.g. by the piano, to a voice or instrument is loosely called an accompaniment, which may be merely "vamped" by the introduction of a few chords, or may rise to the dignity of an artistic composition. In the history of song the evolution of the art side of an accompaniment is important, and in the higher forms the vocal and instrumental parts practically constitute a duet, in which the instrumental part may be at least as important as that of the voice.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)