Much pop and rock music has been very similar in sound, instrumentation and even lyrical content. The terms "pop rock" and "power pop" have been used to describe more commercially successful music that uses elements from, or the form of, rock music. Writer Johan Fornas views pop/rock as "one single, continuous genre field", rather than distinct categories. To the authors Larry Starr and Christopher Waterman, it is defined as an "upbeat variety of rock music" represented by artists and bands such as: Andy Kim, the Bells, Paul McCartney, Lighthouse, and Peter Frampton.