AP® Music Theory · Unit 8 · Topic 8.2
Phrase Relationships and Letter Labels
Phrase-relationship letters track what the melody actually does: a repeated phrase keeps its letter, a varied repeat gets a prime mark, and a genuinely new idea gets a new letter.
A phrase is a musical sentence, usually four measures ending in a cadence. When a tune has two phrases, the second almost always opens the way the first did, so your ear recognizes the tune, then closes differently, so you feel the piece has arrived somewhere. That opening-same, ending-different shape is why so much music feels both familiar and forward-moving at once.
Letters encode exactly that behavior. If the second phrase is identical to the first, it gets the same letter: a, a. If it shares its opening but changes at the cadence, trading a half cadence for an authentic one, say, it is labeled a, a prime, since the material is varied, not new. If the second phrase abandons the opening melodic idea entirely, it earns a fresh letter: a, b. The letter is a melody tracker only. It follows the tune's notes and contour, not the chords underneath, so a melody that repeats exactly but gets reharmonized the second time through still stays a, a. Change the harmony all you want; if the melody is unchanged, the label does not move.
This same labeling habit scales up. Once you can call a pair of phrases a and a prime or a and b, you can describe whole sections the same way: a binary form is built from two sections, often labeled A and B, and a ternary form returns to its opening material for a labeled A B A. Phrase letters are the small-scale version of the same listening skill that names the large sections of a piece.
Key terms
- phrase
- A musical idea, typically about four measures, that ends with a cadence.
- a, a prime
- Labels showing a phrase repeats another's opening but varies its ending or details.
- a, b
- Labels showing two phrases use contrasting melodic material throughout.
- cadence
- A harmonic goal that closes a phrase, ranging from a strong final arrival to a weaker pause.
Watch it explained
- How it worksHow do the labels for literal repetition, varied repetition, and contrast encode what you hear?
- Worked exampleFind the phrase labels for a melody whose second phrase repeats the first with a new ending.
- Common mistakeWhy doesn't a repeated phrase set to different harmony get a brand new letter?
- Ties togetherHow do repeated and contrasting phrase labels set up the sectional letters used in binary and ternary form?
Check yourself
End of topic.