Thematic transformation (also known as thematic metamorphosis or thematic development) is a musical technique in which a leitmotif, or theme, is developed by changing the theme by using permutation (transposition or modulation, inversion, and retrograde), augmentation, diminution, and fragmentation. It was primarily developed by Franz Liszt and Hector Berlioz. The technique is essentially one of variation. A basic theme is reprised throughout a musical work, but it undergoes constant transformations and disguises and is made to appear in several contrasting roles. However, the transformations of this theme will always serve the purpose of "unity within variety" that was the architectural role of sonata form in the classical symphony. The difference here is that thematic transformation can