Sonata Form

Form / Structure

Sonata form is the most important structure in classical instrumental music. It isn't a kind of piece but a way of organizing a single movement, and it shapes the first movements of most symphonies, sonatas, string quartets, and concertos from the Classical era onward. Despite the name, it's not limited to sonatas at all - which is why it's worth learning on its own.

At heart, sonata form is a story in three acts: two contrasting ideas are introduced, thrown into conflict, and finally reconciled.

The exposition: setting out the ideas

The exposition presents the movement's main material:

The first theme (or first subject), in the home key - often bold and memorable.
A transition (or bridge) that moves away from the home key.
The second theme, in a new key - usually the dominant (five notes higher) for a piece in a major key, or the relative major for a piece in a minor key. It often contrasts in character: gentler, more lyrical.
A closing section that rounds off the exposition in the new key.

The crucial point is the key change. Ending the exposition away from home creates a tension that the rest of the movement has to resolve. In 18th-century works the whole exposition is usually repeated, giving listeners a second chance to learn the themes.

The development: conflict

The development takes the exposition's material and puts it under pressure. Themes are broken into fragments, combined, turned upside down, and passed between instruments, while the music moves restlessly through different keys, often far from home. This is the most unpredictable and dramatic part of the movement. It usually ends with a passage called the retransition, which builds anticipation for the return home.

The recapitulation: resolution

The recapitulation brings back the exposition's themes, in the same order - but with one vital difference: the second theme now returns in the home key. What was once a conflict between two keys is now resolved, and the movement ends where it began. The transition is rewritten so that it no longer leaves home.

Many movements end with a coda ("tail"), a closing section that can be just a few bars or - as Beethoven liked to make it - almost a second development. Some movements also begin with a slow introduction before the exposition proper.

Hearing it: Mozart's Symphony No. 40

The first movement of Mozart's Symphony No. 40 in G minor is a perfect example:

Exposition - the violins open with the famous restless first theme in G minor. After a transition, a gentler, sighing second theme arrives in B-flat major, the relative major. The exposition is then repeated.
Development - fragments of the opening theme are tossed around the orchestra and driven through distant keys, growing more and more anguished.
Recapitulation - the opening theme returns in G minor. This time the second theme comes back in G minor too, now darkened, and the movement ends in tragedy rather than resolution into major.

Variations on the plan

Sonata form is a flexible framework, not a rigid rule. Variants include:

Sonata-rondo - a hybrid with a returning refrain, common in finales. See rondo.
Concerto form - in a concerto, the orchestra often presents the themes before the soloist enters.
Sonatina - a small sonata form with a very short development or none at all, beloved of piano students.

Composers also stretched the form: Romantic composers introduced more themes, wider-ranging keys, and longer developments, and 20th-century composers continued to use its basic plan even in very different musical languages.

A form named after the fact

Haydn, Mozart, and Beethoven never used the term "sonata form." They simply composed this way. The name and the textbook description came later, from 19th-century theorists such as Adolf Bernhard Marx, who analyzed the Classical masters' music to explain how it worked.

Where to start listening: the first movement of Mozart's Symphony No. 40 follows the plan clearly; listen for the moment, near the middle, when the opening theme returns - that's the recapitulation. Then try the first movement of Beethoven's Symphony No. 5, with its famously expanded coda. See also our symphony page.