 Christgau, writing in 1972, said in spite of some exceptions, "rock and roll usually implies an identification of male sexuality and aggression".Since the term "rock" started being used in preference to "rock and roll" from the late-1960s, it has usually been contrasted with pop music, with which it has shared many characteristics, but from which it is often distanced by an emphasis on musicianship, live performance, and a focus on serious and progressive themes as part of an ideology of authenticity that is frequently combined with an awareness of the genre's history and development.According to Simon Frith, rock was "something more than pop, something more than rock and roll" and "[r]ock musicians combined an emphasis on skill and technique with the romantic concept of art as artistic expression, original and sincere".