Practice Journal – Opus Numbers and a Small Discovery

While working on Beethoven’s Les Adieux Sonata, Op. 81a by Ludwig van Beethoven, I became curious about that small but unusual “a” in the opus number.

At first, I assumed it had something to do with grouping or multiple related works. But looking into it more closely, I found that the reason is actually much simpler and quite interesting.

the front page of Beethoven piano sonata Opus 81a

The “a” in the opus number is not a musical marking, but a practical solution to a historical issue. Another work by the composer Twelve German Dances, now catalogued as WoO 13, was later assigned the opus number 81 by publishers after Beethoven’s death. This created a duplication, so the sonata was labelled Op. 81a to distinguish it. This small detail highlights how naming conventions are sometimes shaped by publishing history rather than purely by the composer’s intentions.

How Classical Music Works Are Named: Opus, WoO, and Catalogue Systems

The most familiar system is the opus number (Op.). Opus numbers are typically assigned to works either by the composer or by the publisher. They usually follow the order of publication rather than the order of composition. This means that a piece with a lower opus number is not always earlier in composition. In some cases, if more than one work is associated with the same number, letters such as “a” or “b” are added—for example, Beethoven’s Op. 81a. While opus numbers are useful, they are not always perfectly consistent, as they can be influenced by publishing decisions.

For works that were never given an opus number by the composer, the WoO system (Werke ohne Opuszahl) is used. This German term means “works without opus number.” These pieces are often early works, sketches, fragments, or compositions that were published after the composer’s death. In the case of Ludwig van Beethoven, many such works are catalogued under WoO numbers. These are typically organised by scholars in an attempt to place them in a logical, often chronological order.

In addition to opus and WoO numbers, some composers have their own catalogue systems, created by musicologists to organise their complete works more accurately. For example, Johann Sebastian Bach’s works are catalogued under BWV (Bach-Werke-Verzeichnis), Wolfgang Amadeus Mozart’s works use the Köchel catalogue (K.), and Franz Schubert’s works are listed with Deutsch numbers (D.). These catalogues aim to reflect a more reliable chronology and provide a comprehensive overview of each composer’s output.