The model
The “sentence” (Schoenberg, later systematized by William Caplin) is the other major model of the 8-bar phrase:
- Presentation (bars 1–4): a 2-bar basic idea repeated (identically or transposed, often first on the tonic and then on the dominant).
- Continuation (bars 5–8): fragmentation of the idea into shorter units, acceleration of the harmonic rhythm, sequences, and a cadence.
Proportions 2 + 2 + 4, or in miniature 1 + 1 + 2.
Example in C major
- Bars 1–2: motive E–G–C over C.
- Bars 3–4: the same motive transposed (F–G–B) over G7.
- Bars 5–6: one-bar fragments over Am and F (only the beginning of the motive).
- Bars 7–8: Dm – G7 – C, cadence.
Period versus sentence
The period is “question and answer”; the sentence is “state, restate, develop, conclude.” Many themes combine the two: a period whose antecedent is a small sentence.
In pop
The “short–short–long” structure is everywhere: two parallel short lines followed by a longer line that resolves. It works in choruses, in rap hooks (two identical bars and a closing one), in synth riffs.
Real-world example
The opening of Beethoven's Piano Sonata Op. 2 No. 1 (1795) is the textbook example: a two-bar basic idea in F minor, repetition on the dominant, fragmentation and cadence. The Fifth Symphony also begins with a presentation (the motive and its repetition a step lower) followed by a fragmented continuation.