Variation forms are among the simplest and most characteristic of Baroque forms. Although they are not as common as other forms, they project the Baroque desire for systematic, thorough structures in a very direct way. This is because variation form entails the successive, uninterrupted repetition of one clearly defined melodic unit, with changes that rouse the listener’s interest without ever losing touch with the original unit, or theme.

That theme may be a complete melody in the soprano range or a shorter melodic phrase in the bass. Given the emphasis in the Baroque era on the basso continuo (see page 82), it is not surprising that Baroque variations tend to occur above repeating bass patterns. A name for such patterns is basso ostinato, meaning “persistent” or “obstinate” bass. Sometimes the bass itself is slightly varied — though never in such a way as to hide its identity. Dynamics, tone color, and some harmonies are often changed in variations. Tempo, key, and mode are changed less often.

There are a number of names for compositions in variation form, which grew up independently all over Europe, first as improvisations — opportunities for impromptu display on various instruments — and then as written-out compositions. Besides the French chaconne and the Italian passacaglia (pah-sa-cáhl-ya), there was the English term ground (the repeating bass figure being called the ground bass). One seventeenth-century Italian composer, Girolamo Frescobaldi, left a passacaglia for organ with exactly a hundred variations. More compact examples of variation form sometimes appear as one movement in a larger Baroque genre, such as a concerto.*

The term ostinato has come to be used more broadly than just for repeating Baroque bass lines. It can refer to any short musical unit repeated many times, in the bass or anywhere else, especially one used as a building block for a piece of music. Ostinatos are by no means unique to European music; in some form they are found in almost all musical traditions (see, for example, pages 94 and 201).