TERNARY FORM

musical form consisting of three sections, the last of which is a repeat of the first. The symmetrical construction of this scheme (aba) provides one of the basic shapes in music and may be found as a guiding principle in music from the Middle Ages (in Gregorian chant, for instance, the arrangement antiphon-verse-antiphon is common) to the 20th century (a well-known example being the Minuet and Trio from Arnold Schoenberg's Piano Suite, Opus 25). Although any kind of aba pattern may correctly be defined as ternary, the term most precisely denotes that form exemplified by the minuet and trio of the Classical symphony. Basic to the form in this strict definition is the requirement that each of its sections forms an intelligible musical entity, relatively complete within itself. Thus section a forms a logical whole, which is harmonically closed; i.e., it ends in the key in which it begins. It is most frequently in binary form, a variety of two-section form. The same may be said about section b, which is placed in a key different thanthough closely related tothat of section a. The origins of ternary form (still speaking in the strict sense) may be found in the Baroque instrumental suite, in which two dances (most often a minuet and trio) are performed in the standard aba pattern. It survived into the Classical era as the combination of minuet (or scherzo) and trio that serves as the third movement of the typical Classical symphony. In his symphonies No. 4 in B-flat Major and No. 7 in A Major and his String Quartet in E Minor, Opus 59, No. 2, Ludwig van Beethoven modified the form by giving both the a and b sections an extra repeat, thus producing a five-part (ababa) form. The even more striking phenomenon of a second trio (abaca) may be seen in the symphonies No. 1 in B-flat Major and No. 2 in C Major of Robert Schumann and in Anton Bruckner's Symphony No. 7 in E Major.