Rondo

Rondo form is built around a recurring theme — the refrain — that returns in the tonic key after each contrasting episode. The basic rondo pattern is ABACA (five-part rondo) or ABACABA (seven-part rondo), where A is the refrain and B and C are contrasting episodes in different keys. The refrain is typically a complete, self-contained theme in a simple periodic or rounded-binary structure, strongly characterized so that its returns are immediately recognizable. The form's appeal is the balance between the security of the familiar refrain and the variety of the episodes.

The refrain always returns in the tonic key, providing stability and a point of harmonic reference. The episodes depart to related keys — the dominant, relative major, parallel minor, or other closely related areas — and typically use contrasting thematic material. In some rondos the episode material is entirely new; in others it develops or varies material from the refrain. The transition from an episode back to the refrain often involves a retransition passage that re-establishes the tonic and creates anticipation for the familiar theme.

Rondo movements frequently appear as finales of multi-movement works (symphonies, concertos, sonatas) because their episodic structure creates a feeling of playful momentum and their refrain returns give the listener recurring moments of pleasure. The five-part rondo ABACA is the most common form in Classical finales. In the 18th century, composers including Haydn and Mozart sometimes blended rondo and sonata logic into the "sonata-rondo" form (ABACABA with the B sections functioning like the secondary theme of a sonata exposition and recapitulation), producing movements that combine the episodic charm of rondo with the tonal argument of sonata form.