The close similarities shared by hard rock and heavy metal can make it difficult to identify their differences. Both genres have similar, even at times overlapping, origin stories. Musically, they both include loud guitars, pounding drums, driving rhythms and often vitriolic vocals. However, each genre has its own defining characteristics, from its place in the musical lexicon to the technical specifications of its musicality.
Origins
The 1960s saw the birth and popularization of rock and roll by way of such bands as The Beatles, the Rolling Stones and The Kinks. Though certainly controversial at the time, the early sounds these bands produced were light and poppy but gave way to a whole host of young musicians armed with guitars and a love for the blues.
History vs. History
Taxonomically speaking, the classification of hard rock has existed longer than heavy metal, but not by much. Led Zeppelin is often credited as the original hard rock band, followed by such acts as Cream, The Who and Deep Purple. Though similar in sound and scope, and most assuredly influenced directly by hard rock, the origins of heavy metal music trace back to 1970s bands like Black Sabbath and Steppenwolf. The burgeoning of the movement signified a turn from the more melodic hard rock genre into exactly what the name "heavy metal" suggests: heavier sounds and darker themes.
Musicology
Because hard rock’s musical influences root themselves firmly in the blues, its main musical components often include virtuosic guitar and loose, swaggering bass and drum lines. The genre's most famous guitarists include the likes of Jimmy Page, Pete Townsend and Jimi Hendrix—all standout musicians. While hard rock remains complex and melodic, the musical composition of heavy metal remains simpler, and obviously louder, and features less blues influence—especially in the way of syncopation. Often quite muscular, a heavy metal band’s rhythm section features three main characteristics: speed, power and precision.
Fans and Commercialism
Some bands—especially Led Zeppelin and Black Sabbath—often find themselves lumped into both genres, which causes confusion for those trying to differentiate hard rock from heavy metal. To cut through this confusion, taking a look at other, nonmusical factors can help separate one genre from the other. Many heavy metal bands, because of their less-accessible musical attributes, rarely find commercial success, with the possible exception of a band like Metallica. The same principle does not apply for many hard rock bands, such as Van Halen and Aerosmith, two of the biggest-selling artists of any musical genre, who have won fan bases much broader and much more mainstream than those generally enjoyed by heavy metal bands.
Cult Followings
Though hard rock has a large share of devotees, its fans lack the type of rabidness often exhibited by heavy metal fans. Many metal bands are assigned a “cult status," thereby making many of their fans, in turn, de facto cult members who adopt lifestyles parallel to that of the bands’ images. Heavy metal's fan base, often considered a “subculture of alienation,” largely comprises young white males who adopt a certain fashion and boast of a separation from the rest of society.