Binary form is an
AB form, where you have two contrasting musical parts in the piece. However in practice, each part is often repeated once, creating an
AABB structure which can be notated as follows:
Rounded Binary Form
A rounded binary form is like a repeated binary form, but with a return to the
A part in the second repeat. This "rounds off" the piece, and creates a sense of narrative. It can be notated as follows:
Sonata form is not a ternary form; it developed from rounded binary form. It is a development from opera.
The exposition is section
A, which is normally repeated in full. The development and recapitulation form section
B together, and is also repeated.
As sonata forms developed, this binary structure was gradually lost.
The exposition sets out contrasting themes and keys. It begins with an introduction in the tonic key, then leads into the first subject. The first and second subjects are separated by a transition, then it is ended with a codetta.
The exposition has two main themes, which we call the first and second subjects.
The first subject is a statement of the melody in the tonic key. The second subject is a contrasting idea in a related key; normally the dominant or relative key. This results in a modulation between the subjects handled by the transition, usually
I -> V in major and
i -> III in minor.
The development takes the ideas heard in the exposition and develops them. It can be understood as an exploration of the tension created by the contrasts between the first and second subjects.
Examples of Development
- Motifs and short phrases from the exposition may be examined or extended.
- New themes may be added.
- Tonal contrasts are extended as different keys are explored.
The recapitulation resolves the contrasts in key, bringing back together the two subjects.
Transition Between Subjects
In the exposition, the function of the transition between the two subjects is to modulate from the tonic to a related key. However, in the recapitulation both subjects are in the same tonic key. As a result, the transition becomes a bit of a crunch point - since it needs to not modulate.