classical 101 : a guide to numbers in composition titles

When at a concert reading a program or scanning through classical works on iTunes, you will always see abbreviations followed by numbers. But these abbreviations can (and will) vary with each composer…or sometimes there are multiple abbreviations in the name of a work. Without training in music…its probably easier to just ignore these…but if you ever wondered what they all mean, here’s a basic run down.

Op. (or the plural “Opp.”)

Opus Number : Started in the 1600s, the opus number basically serves as a label for composers to note what order they composed their works in. If I composed a work now, i would label it “Op. 1”, and my next composition would be “Op. 2” and so on. Ideally, you would be able to line up all the works by opus number and have a chronological catalog of all the works in a composer’s output, whether the works were published or not. Opus numbers are the standard…but sometimes there are exceptions that have to be dealt with differently…which leads us to the other notations.

ex. Cello Concerto No. 1 in A minor, Op. 33


Works without opus number : Most commonly seen with Beethoven, “WoO” is listed whenever a work was completed/published but not given an opus number by the composer. The why is typically up for debate : maybe they forgot, maybe they didn’t intend to finish it or maybe it wasn’t meant to be published with their other works. Sometimes it is a lost work that is rediscovered and it can’t be placed in their output. However, “WoO“‘s can also be numbered (usually chronologically), as shown in the example below.

ex. Rondo for piano and orchestra in B-flat major, WoO 6

Op. Posth.

Posthumous opus number : The composer died without providing an opus number (usually on unfinished or unpublished works) and they are published after his death by his next of kin. Sometimes they are not numbered…as where with other composers, like Mendelssohn, they can be given actual opus numbers (eg. Symphonies No. 4 + 5).

ex. Waltz in E major, Op. posth.

Why this system doesn’t always work :

Apart from composers inconsistently labeling their works, other issues have come up. A composer may start a piece with one opus number, put it on the shelf for a while, and when they return to it years later, give it a new opus number to their revised version…resulting in numbers for the same piece. It was also common practice to have a group of pieces under the same opus number; Beethoven’s three “Rasumovsky” string quartets are all labeled as “Op. 59”. This is where musicologists get frustrated and re-catalog a composer’s works chronologically under a new system, which is where the other abbreviations come from…making it possible to see both an opus number and the number of a separate library system, showing both how the composer and subsequent historians have cataloged it. Here are some of the most common symbols you’ll run into by composer. The names of the systems are typically the last names of the person who created it.

J.S. Bach : BWV (Bach Work Catalogue)

Mozart : K (Kochel number, probably the most successful catalogue, since Mozart’s original opus numbers are now almost never referred to)

Haydn : Hob (Hoboken numbers) <—who doesn’t enjoy saying hoboken?

Schubert : D (Deutsch numbers)

Hope this helps out the next time you’re wondering what all the numbers mean. Happy listening!