Period and sentence – free music theory course

In classical music, phrases combine according to two main 8-bar models, which every pianist meets on every page of Haydn, Mozart or Beethoven.

The period: question and answer

A period is made of two phrases: an antecedent (the question), ending on a weak cadence — often a half cadence — and a consequent (the answer), which starts the same way but ends on a perfect cadence. The ideal example: Beethoven's “Ode to Joy”.

M:4/4
L:1/4
K:C
"C"E E F G | "G"G F E D | "C"C C D E | "C"E3/2 "G"D/ D2 |
"C"E E F G | "G"G F E D | "C"C C D E | "G"D3/2 "C"C/ C2 |]

Bars 1-4: the antecedent stops on D, over the dominant chord (half cadence): the music asks a question. Bars 5-8: the consequent repeats the same opening and concludes on C (perfect cadence): the answer. When both phrases start the same way it's a parallel period; otherwise, a contrasting period.

The sentence: presentation and continuation

The second model (the sentence, a term coined by Arnold Schoenberg) works differently:

Presentation (bars 1-4): a 2-bar basic idea, then its repetition (often transposed onto the dominant);
Continuation (bars 5-8): the idea fragments into shorter units, the harmonic rhythm speeds up, and it drives toward the cadence.

M:4/4
L:1/4
K:C
"C"c2 e g | e2 c2 | "G7"B2 d f | d2 B2 | "C"c e "F"f a | "Dm"f d "G7"B d | "C/G"e2 "G7"d2 | "C"c4 |]

The 2 + 2 + 4 scheme creates momentum: state, repeat, then accelerate to the goal. The opening of Beethoven's Sonata Op. 2 No. 1 is the textbook example.

For performance: in a period, let the “question” be heard (a slight suspension at the half cadence, without slowing heavily) and then the more conclusive “answer”. In a sentence, let the continuation gain energy up to the cadence.

Not every phrase is “square”: composers extend, compress and overlap these models. They are nonetheless an excellent lens to start with.