Where is the line between hard rock and heavy metal and does it really matter? Who is the forerunner of heavy metal? A lot of people will tell you Tony Iommi is the godfather of metal and that Black Sabbath is the first real heavy metal band. To me, Black Sabbath is a hard rock band all the way, although lyrically and visually they had some elements now associated with the heavy metal genre that may lend credibility to the assertation that Black Sabbath is a metal forerunner. As far as I am concerned, you could make the same argument for Ozzy once he struck out on his own. He certainly introduced a sound and visuals that have become synonymous with the genre.
Bands like Judas Priest brought the metal sound more to the forefront by leaving the blues influence out of the music and focusing more on the highly distorted guitar sounds, the metal imagery, and metal-oriented lyrics. Motörhead, to me, could be classified as metal, but the lyrical and visual elements are primarily hard rock.
A Google search for metal bands will yield lists that I think are rather loose in their interpretation of what bands are considered heavy metal. Kiss, for instance, frequently appears on such lists. By no means do I think of Kiss as a metal band. I love Kiss, but heavy metal they are not.
Glam metal, pop metal, commercial metal, death metal, industrial metal, punk metal - I guess if you start putting more specific labels on bands, you could surely classify more bands as metal, but it begins to border on petty when we get to that point.
Bands that are undeniably metal include Metallica, Anthrax, Slayer, and Megadeth. These bands cannot be classified as anything else. Judas Priest is metal, to be sure, but not hard enough (and sometimes a bit too polished) for some of the die-hard metal lovers. I'd like to see some comments regarding Judas Priest and their position in the metal hierarchy.
Glam metal bands (also referred to has hair metal) include Poison, Ratt, Dokken, Kix, and Helix. Bands like Cinderella, Bon Jovi, and Great White often get thrown in here, though these bands fall more clearly in line with the hard rock genre for me. Whitesnake (a band I adore) went from being a blues-based rock band in the seventies to a wanna-be metal reinvention in the eighties and beyond.
You can argue the finer points of this topic forever. In the end, I'm not sure how much it matters. A good band is a good band. Good music is good music. Label it what you will.
