Homotonal (same-tonality) is a technical musical term pertaining to the tonal structure of multi-movement compositions. It was introduced into musicology by Hans Keller. According to Keller's definition and usage, a multi-movement composition is 'homotonal' if all of its movements have the same tonic (keynote). The classical composer most closely associated with the homotonal principle is Joseph Haydn. Keller himself was keen to emphasise that different classical composers showed differing degrees of interest in homotonal structure: