The book chapter (Ch. 12: Phrase Structure and Grouping) is relatively clear, so I’m not going to rehash everything from it, or class, here. I’ll just post some useful things to remember.
Phrase lengths are typically multiple measures of two, with four being the most common. Since pickups balance out at beginning and end to make a full measure, you don’t count the pickups as a measure.
Phrases usually have a strong cadence to mark their end. If you don’t find a strong cadence, it probably isn’t a phrase ending. Remember that you don’t end a half-cadence on V7 — only on V (the triad).
Tempo and strength of cadences help to determine phrase endings. In very slow tempos it isn’t unusual to have two measure phrases. In faster tempos, eight measure phrases often appear.
Two phrases can group together to form a period. Periods have an antecedent and consequent relationship, usually through open and closed harmonic cadences. Additionally, we can specify if a period is parallel or non-parallel based on the thematic content of the two phrases. Double periods can occur when two periods from and antecedent/consequent relationship. Usually the first period will end on a half-cadence, and the second period will end on an authentic cadence.
Phrases that don’t form period relationships can be referred to as phrase groups.
Miniature formal design refers to the grouping of phrases thematically. We’ve covered binary, song form, and ternary.
Phrases tend to repeat at the same length. We refer to this property as phrase periodicity.
Extension of phrase length happens either through cadential extension with rhythmic emphasis on the final cadential harmony (most often), or through internal extension (something added or repeated not at the cadence).
Contraction of phrase length is also possible. This most often occurs from simply dropping measures (all or part) from a thematic repetition of a phrase. Elisions are different. Phrases that elide share the same ending measure (first phrase) and beginning measure (second phrase).
Phrases can subdivide internally. Any subdivision of a phrase is a sub-phrase.
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