The announcement that Led Zeppelin, the rock'n'roll deities of the early 1970s, are to reunite for a tour without their singer Robert Plant calls many important issues into question. One is the issue of authenticity.

Can the band present itself to its worshippers as the genuine article, when it lacks Plant's unique falsetto screech? They may point to several instances when a replacement singer has been, as it were, grafted on to the vestigial musical body: Paul Rogers replacing the late Freddie Mercury as front man of Queen, Ronnie James Dio standing in for Ozzy Osbourne in Black Sabbath, similar substitutions in Deep Purple, Motley Crue and Iron Maiden. They seldom work.

When Phil Collins replaced Peter Gabriel as singer with Genesis, the band nosedived into mediocrity. Next month sees the 1970s stadium band, Yes, reforming for a tour in which the straining falsetto of Jon Anderson will be substituted by Benoit David, whose stage experience has been confined to Yes tribute bands in Canada. So we must ask: if the singer is a professional Yes fake, why should fans accept the new-look Yes as authentically Yes?

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In the case of Led Zeppelin, our confusion is compounded by two things. First, the talented Mr Plant cannot now quite reach the astonishing high notes to which he once had unfettered access. Should a replacement singer mimic Plant's incapacity, or should he be employed because he can sing as high as Plant used to? If the latter, does this make him "better" than the genuine Robert Plant? Second, the drummer on the Led Zeppelin tour will be Jason Bonham, son of the late John Bonham, the band's original drummer. Jason was barely alive in the Zeppelin heyday, but has been accepted by fans as a kind of mystical manifestation of his father. Is he, therefore, "the real thing" by some genetic osmosis?

All of which enquiries are as chaff in the wind to the average Zeppelin fan, who will happily pay £100 for a ticket to the new tour. Those who attended the band's one-off 02 Arena gig last year speak of the experience in hushed whispers, as the greatest rock gig in history.

To suggest that the fans were merely adulating their own fiery, long-haired youth, and will continue to do so, would be cynical; but clear thinking is not part of the rock fan's mental repertoire. As long as it summons up their past with sufficient conviction, they will love a reunion by Sham 69 or Blodwyn Pig or Dave Dee, Dozy, Beaky, Mick and Tich – even if aware that Mick and Tich have been replaced by people with quite different names.

The only person who emerges with dignity out of rock music's current strip-mining of the past is Robert Plant. No amount of cash will persuade him back on the yellow brick road, while he pursues his new interest in making beautiful music with the country fiddler Alison Krauss. A 1970s musician who puts creative exploration above money? It's not very rock'n'roll, is it?

j.walsh@independent.co.uk