Developing variation
In musical composition, developing variation is a formal technique in which the variations are produced through the development of existing material. The term was coined by Arnold Schoenberg, twentieth-century composer and inventor of the twelve-tone technique, who believed it was one of the most important compositional principles since around 1750: Music of the homophonic-melodic style of composition, that is, music with a main theme, accompanied by and based on harmony, produces its material by, as I call it, developing variation.