I won't call the author right or wrong on their categorizations, but metal - and maybe all genres of music - break down in the following ways: 1) Subject matte

I won't call the author right or wrong on their categorizations, but metal - and maybe all genres of music - break down in the following ways: 1) Subject matter, which for long-running bands tends to have a fad-like flavor (e.g. AC/DC's Highway to Hell and Back In Black have more satanic subject matter than DDDDC or Fly On The Wall.) 2) Presentation / aesthetics / "Dress code" -- For instance, Van Halen vs. Mötley Crüe. Both wore spandex; MC also wore obvious makeup, dyed / teased hair, and sort of shambling / fishnet clothing, VH did not. Black Sabbath tended a little more towards leather and black, while their equally-loud peers Led Zeppelin looked a little more hippy. 3) Band composition / Musical direction -- For instance, it is nearly impossible to call your band metal if it has a keyboard player (Sorry Styx and Deep Purple.) How about guitars? Some bands - GnR and Aerosmith had dedicated lead and rhythm guitarists, who harmonized a little; Other bands, such as Priest and Iron Maiden, had more-or-less two lead guitarists who would split leads and/or harmonize multiple times per song. Just a forinstance, KISS would be metal based on 2, but not so much 1 (their subject matter was mostly sex and drugs, very little death and hell.), and their approach to 3 was pretty much Rick Derringer territory.