Relationship with classical music
Ritchie Blackmore, inventor of Deep Purple and Rainbow, famous for the neoclassical approach in his guitar performances. Robert Walser maintains that, alongside R&B and blues, the "assemblage of disparate musical styles known...as 'classical music'" has been a key influence on heavy metal from the genre's initial days. He asserts that metal's most dominant musicians have been guitar players who have also learnt classical music. Their adaptation and appropriation of classical models sparked the growth of a new form of guitar virtuosity and modifications in the melodic and harmonic language of heavy metal.
Although several metal musicians quote classical composers as motivation, metal and classical are rooted in various cultural conventions and practices—classical in the art music convention, metal in the common music convention. As musicologists Nicola Dibben and Nicolas Cook denote, "Analyses of common music similarly sometimes disclose the influence of 'art traditions.' An example is Walser's linkage of heavy metal music with the ideologies and even some of the performance practices of nineteenth-century Romanticism.
According to researchers Stephen Millward and David Hatch, Black Sabbath, and the several metal bands that they motivated, has specialized lyrically on depressing and dark subject matter to an degree hitherto unprecedented in any type of pop music. They take as an example Sabbath's second album Paranoid (1970), which included songs dealing with personal trauma—'Paranoid' and 'Fairies Wear Boots'—as well as those challenging broader issues, like the self-explanatory 'Hand of Doom’ and 'War Pigs'. Deriving from the version’s roots in blues music, sex is another imperative topic—a thread running from Led Zeppelin's suggestive lyrics to the more overt references of glam and nu metal bands.
King Diamond, known for writing conceptual lyrics about horror stories
The thematic message of heavy metal has for a long time been a target of censure. According to Jon Pareles, "Heavy metal's prime subject matter is easy and almost universal. With grunts, moans and subliterary lyrics, it celebrates...a party without limits. The bulk of the music is stylized and formulaic." Music censures have frequently deemed metal lyrics juvenile and banal, and others who have opposed to what they see as advocacy of misogyny and the occult. During the 1980s, the Parents Music Resource Center petitioned the U.S. Congress to control the famous music industry due to what the group affirmed were objectionable lyrics, specifically those in heavy metal songs. Music censure Robert Christgau termed metal "an expressive mode it sometimes seems will be with us for as long as ordinary white boys fear girls, pity themselves, and are allowed to rage against a world they'll never beat".