"I think there are some objective [musical] qualities... how complex something is, how melodic, how diverse the tonality is, et cetera. But I could also make a piece of music that contains all of those and yet isn't "good" from a subjective viewpoint. For example, take Beethoven's "Moonlight Sonata", Beatles "Yesterday", and Underworld's "Born Slippy", and play them all on top of each other at the same time. Great music in their own right, but terrible sounding together."