Music 160A: Basic Formal Units (Motive, Phrase, Period)

Motive
A motive is a short, distinctive, memorable melodic unit, a "motivating idea...the small cell out of which the music evolves."[1] There are of course many short melodic gestures in a work, but only those few that figure prominently in its growth are designated as motives. It is "the smallest characteristic unit, distinctive in melodic and rhythmic content, whose significance is established in development. [It is] a stimulus to its own development and continuation."[2] The opening of Beethoven's Fifth Symphony is a particularly clear example of a motive, a melodic kernel that has minimal melodic and rhythmic interest by itself, but whose significance emerges over the course of the work.

Phrase
A phrase is "the smallest structural unit that terminates with a cadence."[3] Like a number of music-analytical terms, "phrase" originated in ideas about how verbal communication is organized. A phrase is roughly equivalent to a clause in language, a unit that expresses a single (if incomplete) thought. In music, it is a unit that traces a course of melodic action from a beginning through a midpoint, and from there toward a discernible arrival point, though that arrival may not bring final melodic or harmonic closure. [NOTE: For an example, see the class anthology, p. 1, excerpt 1, mm. 1-4, and excerpt 2, mm. 1-4.

The normal length of phrases in tonal music is four measures, but length is variable. In a slow tempo, it might be two measures, in a fast tempo, eight.

Phrases are often grouped in pairs to create larger units (as in a "period"), though not necessarily (as in a "phrase group"). Because consecutive phrases are generally associated in some fashion, a phrase can generally be understood only in light of its relationship to surrounding ones.[4]

Period
A pair of phrases with complementary cadences, the first inconclusive, the second conclusive, is called a period. The first phrase of the pair is often called the antecedent, the second phrase the consequent. If the second phrase modulates to a new key—for example, to the dominant—we speak of a modulating period.

The contrasting, complementary cadences are the definitive feature of a period, not the melodic content of the two phrases. However, the melodic content does, of course, influence the nature of the period. If the melodic content of the two phrases is similar, perhaps nearly identical (except for their endings, to allow for the contrasting cadences), it is a parallel period, if dissimilar, a contrasting period. [NOTE: For examples of a parallel period, see the class anthology, p. 4, excerpts 13 (Mozart) and 15 (Schumann). For examples of a modulating period, see p. 1, excerpt 4 (Haydn), and page 8, excerpt 24, mm. 1-8 (Mozart).]

Sometimes, four phrases are grouped together in two pairs such that the cadence at the end of the first pair is less conclusive than the one at the end of the second pair, whose cadence is the most conclusive of all. Such a complementary arrangment of two phrase pairs is called a double period. [NOTE: Examples appear in the class anthology, p. 6, excerpt 20, and p. 9, excerpt 25 (both by Mozart).]

Composers may expand phrases and periods by various means, e.g. by repeating a melodic fragment, a measure or measures within a phrase or appending something to it, by lengthening rhythmic values in such repetitions, and so forth. Ignoring such expansions for analytical purposes, we often find that long phrases (longer than the established norm) reduce down to the expected length (e.g. four measures).

Section
A section is a major structural unit, composed of phrases and periods strategically designed (harmonically, melodically, tonally, rhythmically, texturally, etc.) and ordered to convey a sense of purposeful motion toward a final goal (the cadence that ends the section), with intermediate goals along the way (at the ends of phrase groups or periods). Sections are combined in conventional ways to create familiar musical forms (binary, ternary, sonata, rondo). [5]