People often get confused between the terms Hard Rock, Heavy Rock, Heavy Metal - and a whole raft of other terms, and the period of Metal's development from 1971-1975 does nothing to help matters.
The terms are widely used interchangeably to describe bands such as Deep Purple, Led Zeppelin and even Black Sabbath - and all are correct.
The term "Heavy" to describe music orignated in the late 1960s as I said earlier, to distinguish the bands playing music of a darker mood from the lighter bands - especially those that typified the "flower power" sound. "Rock" is a catch-all for all music that originated from Rock'n'Roll, although I think it would be more accurate to say that heavy music had it's origins more firmly in the blues, and the lighter music had it's roots in folk.
Led Zeppelin and Deep Purple were wonderful anomalies, with Zep drawing on both folk and the blues, and Purple drawing unusually on classical music - almost eschewing the blues in favour of rock and roll. Both bands were also borderline prog with their experimental approaches, but on the whole kept themselves firmly in the rock category. The progressiveness and experimental tendencies were probably part of the zeitgeist created by "proper" prog rock bands.
"Hard Rock" is more of a radio term, and doesn't seem to mean very much in and of itself, but as a generalisation, we can consider the bands with a heavy style and a tendency towards a major tonality and with lyrics that were more preoccupied with love/sex to fit this style.
Glam Rock also became popular in the 1971-5 period, with the likes of Marc Bolan and David Bowie, and culmimating in bands such as The Sweet. Glam was typically more romantic, although there was always a tinge of aggression. The Sweet added to the aggression with their "bad boy" attitudes in songs like "Hellraiser", "Ballroom Blitz" and "Blockbuster".
"Metal" is hard to define in this period; There were bands like Uriah Heep, with their prog-rock leanings lyrical content that ranged from love ("Sweet Lorraine") to fantasy ("The Magician's Birthday", "July Morning"). Heep's early material acknowledged the heaviness of the music ("Very 'Eavy, Very 'Umble"), but the overall sound tended towards a major key tonality.
There were a large number of developing American bands around this time; Alice Cooper, signed by Frank Zappa, who had a "heavy metal" sound as early as 1971 presumably based his OTT theatricals on the Crazy World of Arthur Brown and the sound on The New York Dolls, and later Kiss (1973) who would take theatricals to new levels. Also inspired by the NYD and the Rolling Stones, Aerosmith were another major player in the development of metal from the US, with the notable ability to produce both diamond hard ballads as well as hard-rockin' choons with huge riffs and dramatic changes. "Toys in the Attic" (1975) contains fantastic examples of their brutal riffs.
Other major players/albums that shouldn't be overlooked were Frank Marino and Mahogany Rush (Maxoom - 1973) - Frank is notably a man often cited by Steve Vai as an influence, Ronnie Montrose (Montrose - 1973, particularly notable for "Bad Motor Scooter" and "Space Station #5"), Rush (Fly By Night - 1975) and Blue Oyster Cult (Tyranny and Mutation - 1973).
Back in the UK, the Blues and psychedelia were still propelling two major underground players; The Groundhogs (recommended album : "Split") and The Pink Fairies (recommended album "Kings Of Oblivion"). The latter are especially important for their role in defining the Motorhead sound.
Of course, these are still generalisations, and many of these bands went on to redefine their styles later in the 1970s, again in the 1980s and yet again in the 1990s.
The next phase of Heavy Metal is 1975-1979, but the borderlines are very hazy - which is why this period follows on from 1971-1975.
The reasons for this are two bands/albums: "On Parole" by Motorhead, which was posthumously released due to a frightened record company, and "Stained Class" by Judas Priest - both of which are almost unarguably pure heavy metal, but both in very different styles.
Also worth mentioning are a quirky band formed by two Scottish brothers based in Australia, with Glam rocker Dave Evans on vocals. They released a lecherous song called "Can I Sit Next To You Girl", but Evans refused to go on stage, so was replaced by the band's chauffeur. Depite their Australian base, this band of bad boys with a wild sense of humour, whose music was unquestionably based in the blues but with the musical focus on the huge riffs and blues guitar, and lyrical content based on sleaze, would go on to be a major player in the NWOBHM, around 1979.
Any serious ommissions?
I've just thought of one that should have been in the 1967-1970 discussion;
Ten Years After - their contribution to the genre is both legendary and unquestionable - the Woodstock performance being a prime example. Recommended album "Ssssh".
...and Iron Butterfly I guess are kind of proto-metal - although the lyrical content is all wrong. I know Slayer covered "In-A-Gadda-Da-Vida", but then Voivod covered "Astronomy Domine". I wo't make any judgements here, as I can hear the potential for metal in "AD", but far more so in "Careful with that Axe, Eugene". I'm similarly not convinced by Vanilla Fudge, although the lugubrious nature of their interpretations of popular songs certainly resembles Sabbath at their most lumbering.
Edited by Certif1ed