Opus number developed other catalogue-number systems; among them the "Bach-Werke-Verzeichnis" (BWV-number), and the "Köchel-Verzeichnis" (K- and KV -numbers) with which are organised the works of Johann Sebastian Bach and Wolfgang Amadeus Mozart, respectively. In the classical period, the Latin word "opus" ("work", "labour") was used to identify, list, and catalogue a work of art. By the 15th and 16th centuries, the word "opus" was used by Italian composers to denote a specific musical composition, and by German composers for collections of music. In compositional practise, numbering musical works in chronological order dates from 17th century Italy, especially Venice. In common usage, the
John Field (composer) were influenced by these works, which are particularly notable for their central movements, frequently nocturne-like. Some of the less known works were also historically important: particularly the piano fantasies, in which Field pioneered the Romantic large scale episodic structure. None of his piano sonatas, and only two of his 7 piano concertos, have a formal slow movement. In performance, Field would interpolate an existing nocturne in a related key or improvise one. This list is arranged according to Hopkinson numbers, introduced in the 1961 catalogue by Cecil Hopkinson. Many of these works were arranged for other instruments and (or) revised