The Phrase, Archetypes, and Unique Forms

Two archetypal phrase groupings govern most tonal music at the phrase level: the sentence and the period. A sentence is an eight-measure structure (in the normative case) divided into two halves. The first four measures form the presentation, which states a basic idea and then repeats it at the same pitch level or sequentially. The second four measures form the continuation, which fragments the basic idea, accelerates harmonic rhythm, and drives toward a cadence. The sentence thus moves from stability (presentation) through instability (continuation) to resolution (cadence).

A period consists of two phrases — antecedent and consequent — that together form a complete musical statement. The antecedent phrase ends with a weaker cadence (typically a half cadence or an imperfect authentic cadence) that leaves the music feeling unresolved. The consequent phrase responds by repeating or varying the opening material and ending with a stronger cadence (a perfect authentic cadence). The period is defined by this two-phrase dialogue: question (antecedent) followed by answer (consequent). A parallel period begins both phrases with the same basic idea; a contrasting period begins the consequent with new material.

Some phrases do not fit the sentence or period mold. An independent phrase — sometimes called a "phrase" proper — is a single unit that ends with a cadence but does not combine with another phrase to form a larger archetype. A phrase group is a series of phrases that are related but do not form a strict period or sentence. These unique and loosely organized structures are common in folk and popular music, and appear in art music wherever composers depart from the two archetypal models for expressive or structural reasons.