Composers use opus numbers to systematically organize their musical works, typically assigning sequential numbers to their major compositions, such as symphonies, concertos, sonatas, string quartets, and other larger-scale pieces. By adding an opus number to a composition's title, composers provide a standardized and easy way to identify and catalog their works.
For example:
- Ludwig van Beethoven's Symphony No. 5 is commonly known as "Beethoven's Symphony No. 5 in C minor, Op. 67."
- Pyotr Ilyich Tchaikovsky's Piano Concerto No. 1 is often referred to as "Tchaikovsky's Piano Concerto No. 1 in B-flat minor, Op. 23."
Opus numbers are generally assigned chronologically based on the order in which the compositions were published or completed by the composer. However, some composers may choose to assign opus numbers out of order for various reasons, such as when revising an earlier work or publishing a composition posthumously.
Using opus numbers helps catalog and organize composers' works, making them easier to study, discuss, perform, and reference within music history. It also allows scholars, performers, and audiences to understand the chronology and development of a composer's musical output over time.