Binary and Ternary Form

An eight-measure period is not yet a piece. Becoming a piece requires several periods to combine.

What governs the combining is a strikingly simple pair of principles: contrast and return. Present something different, or bring something back. Nearly every form can be described as a distribution of those two.

Binary form — state, then contrast

Binary form consists of two sections, A and B. Present in A, contrast in B. That is all.

Baroque dance movements — allemande, courante, sarabande, gigue — are almost universally this shape. Each section carried a repeat sign, and the convention was to play A twice and B twice.

What matters in binary form is that B differs from A. Continuing with the same material produces one long section rather than two. Change the key, change the melodic direction, change the rhythm — something must contrast before two sections exist.

Rounded binary — binary, but with a partial return

Binary form has a slightly more involved variant: rounded binary.

At the end of B, material from A partially returns.

‖: A :‖: B  A' :‖

With A, B, and A’ laid out in a row it looks like ternary form. But there are only two divisions marked by repeat signs, and B and A’ are treated as one continuous second half — which is why it is classified as binary.

The form matters because it is the model for sonata form. Present in the first half; develop and then return to the theme in the second. Sonata form is that design enlarged.

Simple binary against rounded binary

▶Simple binary▶Rounded binary

Check: The first goes A, then B, and stops. The second brings the opening of A back after B. The only difference is whether anything returns at the end, and yet the second conveys a much stronger sense of having come full circle. Listen for the moment just before the return, where the music hangs.

A (4 measures) + B (4 measures)

Check

A piece runs A (8 measures) – B (8 measures) – A (8 measures), with B and the return of A enclosed together in one repeated span. What is it?

Simple binary formRondo formSimple ternary formRounded binary form

Check answer

Ternary form — state, contrast, return

Ternary form is A – B – A. It differs from binary in exactly one respect: A returns complete.

Consider what the return accomplishes. Throughout B, the listener is holding a memory of A. When A comes back, memory and sounding music coincide, and that coincidence registers as satisfaction.

So a return is a device that converts the listener’s memory into a reward. Which is why an overlong B weakens the effect: nothing is gained by the return of something already forgotten.

With a return, and without

▶A – B – A (with return)▶A – B – C (no return)

Check: The first is A – B – A and the opening shape comes back at the end. The second is A – B – C, with new material every time. Same length, and yet the first closes as a piece while the second sounds like a walk with no destination. Returning is what creates the sense of a whole.

the opening shape returns

Why B ends on a half cadence

The middle section of a ternary form usually ends on a half cadence, and that is no accident.

Closing B with an authentic cadence completes the music at that point. The return of A then sounds not like a return but like a fresh start, and the effect of the return evaporates.

Leaving B open on the dominant instead puts the listener in a state of waiting for resolution. When A comes back, the return itself becomes the resolution. Formal design and choice of cadence are directly linked here.

Check

You close the B section of a ternary form firmly with an authentic cadence in the home key. What happens?

B becomes self-contained and the return of A sounds like a new beginningThe form becomes binaryThe key changesThe return of A is emphasized more strongly

Check answer

Simple and compound — one more level

Ternary form comes in two sizes.

In simple ternary form, A and B are each about the size of one period, and the whole runs to roughly twenty-four measures.

In compound ternary form, A is itself a complete small form. A is a binary form, B — the trio — is also a binary form, and then the whole of A returns. The hierarchy gains another level.

Minuet and trio, and scherzo and trio, take this shape. The instruction to play the minuet da capo after the trio is exactly a direction to return to A.

	Content of A	Overall size
Simple ternary	one period (about 8 measures)	around 24 measures
Compound ternary	itself a binary or ternary form	dozens to over a hundred measures

Formal analysis is framed in terms of nesting because of this hierarchy. Motives make phrases, phrases make periods, periods make sections, sections make pieces. The same two principles, contrast and return, operate at every level.

▶ Compare binary and ternary in the form viewer Switch between binary and ternary form and confirm that the middle section ends on a half cadence Form Viewer →

Everything so far has been Western classical form. The next lesson takes up blues and popular music. The principles are the same, but the placement of divisions and the treatment of repetition are not.