- Leonard G. Ratner
The interval of time between successive events, such as rhythmic pulses or peaks in a vibration pattern; commonly, a musical statement terminated by a cadence or built of complementary members, each generally two to eight bars long and respectively called ‘antecedent’ and ‘consequent’. A musical period has been compared with a sentence, or period, in rhetoric. Zarlino, in Le istitutioni harmoniche (1558), associated the two concepts when he described the cadence as a punto di cantilena, which could not appear until the sense of the underlying text had been completed (p.221); in this sense a period, however short or long, extends until its harmonic action has come to a close. It is this view of structure that governed musical form for much of the 18th century, extending below and above the period itself, from two- and four-bar phrases to entire movements. With the technique of Fortspinnung a composer such as Bach could build long periods out of short figures and motifs; the harpsichord cadenza to the first movement of Brandenburg Concerto no.5, for instance, constitutes a harmonic period 43 bars long (another example, in which a four-note motif in semiquavers is extended to a 12-bar period, is quoted in ...