Binary form

What it means

Binary form consists of two main parts, A and B, that follow one another without the first returning at the end. Both parts are often repeated, which is shown by repeat signs, so that in performance the sequence AABB results. It is one of the oldest and most widespread forms of instrumental music.

Musical use

Binary form is especially formative for the dance movements of the Baroque. Its layout there follows a harmonic plan: the first part begins in the home key and modulates to a related key — in major mostly to the dominant, in minor mostly to the relative major — where it closes. The second part begins in this secondary key, often touches further keys, and returns to the home key. The form is thus harmonically closed, even though thematically no part returns.

Often the second part begins with the material of the first, now in the secondary key, and both parts end with related closing phrases. If, in the second part, the beginning of the first additionally returns in the home key, one speaks of rounded binary form — a layout from which sonata form developed in the eighteenth century.

Binary form is to be distinguished from the ternary song form ABA, in which the first part returns completely after a contrasting part, and from the period, which likewise consists of two halves but forms a smaller unit within a form.

Binary form is typical of Baroque dance movements: the first part modulates to the dominant or the relative key, the second leads back to the home key; both are repeated. Sonata form developed from it.

Performance practice

Make the harmonic plan clear to yourself: where does the first part modulate, how does the second return? Shape the close of the first part as a provisional goal and that of the second as the final one. Agree within the ensemble whether repeats are played, and shape them slightly differently, so that the second pass is audible as a deliberate repeat.