Period
Usually an eight-bar formal unit of antecedent and consequent.
What it means
A period is a closed musical idea made of two halves related to each other: antecedent and consequent. In its basic form it comprises eight bars, four for each half. The two parts relate to each other like question and answer.
Musical use
The relation rests on two features. First, the shared beginning: the consequent usually begins with the same material as the antecedent, so that the kinship is audible. Second, the different ending: the antecedent ends open, typically with a half cadence on the dominant, the consequent closes with a full cadence on the tonic. The question stands still, the answer concludes.
The period is one of the basic models of tonal music and especially widespread in the Viennese Classical period, in dance movements, and in songs. It occurs in numerous variants: antecedent and consequent can be lengthened or shortened, the consequent can modulate into another key, and several periods can be joined into larger units.
The period is to be distinguished from the so-called sentence, the other basic model of Classical theme formation: there, a short basic idea is first repeated and then continued in a Fortspinnung that presses toward the close. The period is symmetrical and resting in itself, the sentence forward-directed. Many themes combine features of both models.
Strictly speaking, the period is more than a phrase: the period consists of phrases but is itself a larger unit.
The classical period is eight bars long and organizes into a four-bar antecedent with a half cadence and a consequent with a full cadence that takes up the antecedent. It is distinguished from the sentence, which consists of presentation, Fortspinnung, and cadence. The period is typical of themes of the Viennese Classical period, dances, and songs.
Performance practice
Shape the antecedent as open and the consequent as concluding — the difference should be audible. Keep the tension across the half cadence. And do not shape the shared beginning of both halves identically; the second knows what the first has asked.