Q1: Why does this article include hard rock bands like Led Zeppelin and Deep Purple who are not heavy metal?

A1: Reliable sources support the view that bands like Led Zeppelin were considered heavy metal in their time and were major pioneers of the genre in its early stages. There has been a long-standing consensus to include an explanation of their role in the article.

Q2: Why is hard rock not one of the stylistic origins in the infobox.

A2: Hard rock and heavy metal were used interchangeably for at least a decade, therefore one is not the progenitor of the other.

Q3: Didn't Black Sabbath invent heavy metal, for example by adopting the tritone?

A3: Black Sabbath made an important contribution to the development of heavy metal, but reliable sources indicate that they were only one of a number of bands that contributed to that process.

Q4: Aren't metal and heavy metal different genres?

A4: Reliable sources indicate that metal is just an abbreviation for heavy metal. The terms are sometimes used in different contexts, but it would be confusing to have separate Wikipedia articles about what is essentially the same genre.