|Art Rock, also known as Progressive Rock, is in essence, music with ambition. The focus is on musical content and expression rather than adherence to traditional rock formulas. In every case successful progressive rock is music which aspires to, and attains, higher levels of art than can be achieved by simple dance music (which is what rock, at bottom, is). Because rock itself is based on two simple forms - 32-bar pop songs, or 12-bar blues - any attempt to extend it beyond these forms calls into use advanced or extended forms of music. These forms of music incorporate a wide variety of compositional influences from the Renaissance, Baroque, Classical, and Romantic periods, as well as more modern styles like jazz, post-modern and neo-classical styles and even blues, folk, heavy metal and electronic. Art Rock is also characterized by the frequent inclusion of mixed and uneven/asymmetrical timing.