Phrases in Combination
Updated: 2026-07-04Phrases rarely stand alone — they combine into larger units. To describe how phrases combine, we first need to distinguish how conclusively a cadence ends.
Key takeaways
- A Perfect Authentic Cadence (PAC) needs all three: V→I, both chords in root position, and the tonic in the top voice; miss one and it's an Imperfect Authentic Cadence (IAC).
- A sentence repeats or sequences an idea, then develops toward a cadence — a common model is 2 + 2 + 4 measures.
- A period is at least two phrases where the last one ends more conclusively than the first.
- The two phrases relate like question and answer: antecedent (less conclusive) and consequent (more conclusive).
- An asymmetrical period has 3 or 5 phrases; a double period has at least 4, grouped into antecedent and consequent groups.
How do perfect and imperfect authentic cadences differ?
The difference is those three requirements: a perfect cadence meets all of them, an imperfect one misses at least one. We split the authentic cadence (V–I) into two kinds. A Perfect Authentic Cadence (PAC) must meet all three requirements:
- V → I.
- Both chords in root position.
- The tonic (1̂) is in the highest voice of the I chord.
If any requirement is not met (a chord is inverted, the top voice isn't the tonic, or vii° replaces V), it is an Imperfect Authentic Cadence (IAC). The PAC is the most conclusive cadence — usually reserved for important points of arrival.
How is a sentence constructed?
A sentence states an idea, restates it, then develops toward a cadence. A sentence is a phrase with a characteristic melodic construction: a musical idea (a motive or subphrase) is repeated or sequenced, then followed by material leading to a cadence. A common model is 2 + 2 + 4 measures: state the idea — restate it — develop and cadence.
What is a period?
A period is two or more phrases combined, where the last one ends more conclusively. A period consists of at least two phrases, where the final phrase ends more conclusively than the first. This requires distinguishing conclusive from inconclusive cadences:
| Inconclusive (end off the tonic) | Conclusive (end on I) |
|---|---|
| Deceptive cadence (V–vi) | Authentic cadence (V–I) |
| Half cadence (ends on V) | Plagal cadence (IV–I) |
The two phrases relate like a question and answer:
- Antecedent: the phrase with the less conclusive cadence — the "question."
- Consequent: the phrase with the more conclusive cadence — the "answer."
A period is parallel if both phrases begin with similar melodies, or contrasting if they begin differently. The prime mark (as in a′, read "a prime") labels a phrase that resembles an earlier one but ends with a different cadence.
How do asymmetrical and double periods differ?
An asymmetrical period has an uneven count of antecedents and consequents, while a double period groups many phrases into two larger halves.
- Asymmetrical period: made of 3 or 5 phrases, with an unequal number of antecedents and consequents (e.g. one antecedent, two consequents).
- Double period: made of at least 4 phrases, grouped into an antecedent group and a consequent group; the second group ends with a cadence that "answers" the inconclusive cadence of the first.
See Melodic Analysis for phrase and subphrase, and Roman Numerals & Cadences for the cadence types.
Frequently asked questions
What's the difference between an antecedent and a consequent? The antecedent ends with a less conclusive cadence — the "question" — while the consequent ends more conclusively — the "answer." That difference in finality is what gives a period its question-and-answer feel.
How is a sentence different from a period? A sentence is a single phrase with a repeat-and-develop construction (often 2 + 2 + 4 measures), whereas a period combines at least two phrases, with the last ending more conclusively than the first.
What makes a period parallel versus contrasting? A parallel period has two phrases that begin with similar melodies; a contrasting period has two phrases that begin differently.