What is the secret of the work number in classical music?

Have you ever seen the letters “Op.

Op.” is used in the names of classical music works, for example, Chopin’s “Waltz in C-sharp minor, Op. 64-2” and Beethoven’s “Sonata Op. 49-2, 1st movement.

In fact, this is read as “opus,” and each is a work number assigned to a composer’s work to classify it. In Japan, it is sometimes called “Opus No. XX.

There are several different ways to write this work number, the most typical being “Op.

However, there are also work numbers that bear the names of musicologists who have specialized in typing the works of particular composers.

In this issue, we introduce a few of them.

Koechel number (catalogue of Mozart’s music)

The Köchel numbers are used for Mozart’s works and are named after the musicologist Ludwig von Köchel, and are arranged chronologically from K.1 to K.626. Mozart’s last work, K.626, is the famous unfinished “Requiem.

Deutsch number

Deutsch numbers are used for Schubert’s works and are named after the musicologist Otto Erich Deutsch. They are arranged in chronological order, from D1 to D998, but Deutsche himself was particular about the numbering system. The works are numbered D1 through D998 in chronological order, but Deutsche himself is particular about the way in which they are numbered: he wants D to be used only as Schubert’s work number, so they are generally numbered D1 rather than D.1 (because adding a period would imply an abbreviation of Deutsche’s name).

Hoboken number

Hoboken numbers are used for Haydn’s works and are named after the musicologist Antony Van Hoboken.