Compositions for solo voices and piano are almost invariably art songs. They may also be arrangements that fall out of this category, such as fragments from opera or musical theater, reductions of vocal chamber music or orchestral songs, pieces with popular roots and/or folksongs not specifically adapted by a composer, sacred music not intended for concert, etc. In music for solo voice and piano, the piano naturally fulfills an accompaniment role, though the balance of this relation has been an element of exploration for composers during the 20th century.