The New Grove Dictionary of Music, music academia's Bible, gives the following definition of opera: "The generic term for musical dramatic works in which the actors sing some or all of their parts. Opera is a union of music, drama and spectacle." Its most extreme manifestation is Wagner's ideal, the Gesamtkunstwerk - "complete art work", combining music, drama and spectacle to the highest degree.
More generally, when you go to an opera, you expect to see a good story and believable characters, with music that is appropriate, inspired, sophisticated and well performed. You hope to come out moved and uplifted.
A purist, of course, would have plenty of objections to calling Tommy and Quadrophenia operas. For a start, in most operas, you find a variety of musical structures: dramatic scenas, choruses, love duets, solo arias and ensembles where characters simultaneously express different viewpoints. The singers have to act, staying in their roles for the duration.
But the majority of the songs in Tommy and Quadrophenia are simply songs. They progress, in Tommy, one after the other without speech; telling a story, but without the wide variety you'd expect in a "real" opera. In these staged versions, unlike the feature films, the members of the band aren't in costume, and they convey different viewpoints as the stories unfold. The guest artists do adopt characters: in Tommy, Patti Labelle sings the Acid Queen, Billy Idol the bullying Cousin Kevin, and there are guest spots for Phil Collins and Elton John; Quadrophenia features Billy Idol as the Ace Face.
On the other hand, Townshend - who'd penned operas and studied orchestration, but didn't expect The Who to perform such things - lets rip when opportunity allows. Tommy's recurring plaint, "See me, feel me, touch me, heal me", is as raw and vulnerable as anything you'll hear in Covent Garden, though probably not every singer could bring it off as convincingly as Daltrey. And Tommy's overture is as fizzy and galvanising as any Rossini.
Opera traditionally deals with emotion on a grand scale. Tommy and Quadrophenia both involve powerful emotions, springing from a shared underlying theme: the legacy of a generation's wartime traumas upon its children. Unlike many operas other than Wagner's, words and music originate (mainly) with the same creator. Tommy's plot lets it down a bit, requiring major suspension of disbelief: a child witnesses the murder of his father by his mother's lover, turns blind, deaf and dumb in consequence, becomes a pinball champion, then is cured by a smashed mirror and turns into a pseudo-Messiah who nonetheless remains alienated by his experience.
Quadrophenia is more internalised: most of it takes place inside Jimmy's muddled head. Yet this adolescent anti-hero's spiritual journey involves emotions that run so high, with imagery so strong and archetypal, that Townshend borrows directly from Wagner's Das Rheingold to depict a boat journey.
Wagner writes about gods building Valhalla, Townshend about an alienated teenager running away to Brighton; yet their protagonists are tormented to the limits of their experience, whether through godhood or through drink and drugs. Wagner's monumental power matches the myths behind his stories; Townshend's rock soundworld fits Jimmy's angry internal agony to perfection.
It's in Quadrophenia that Townshend really crosses the divide. The four different aspects of Jimmy's mind are each represented by a leitmotif, a Wagnerian association of idea with musical theme, which join together at the climax when Jimmy is stranded on a rock in the sea and experiences his spiritual epiphany. Meanwhile, there's a Gesamtkunstwerk idea, too: in this version, Jimmy's narration is portrayed on film, images of the sea return constantly, and a lengthy instrumental interlude accompanies a montage of newsreel footage, tracing the evolution of teenagers against a background of the Blitz, Hiroshima and The Beatles. What's more, Quadrophenia's subject matter - growing up - is timeless.
In some ways, Quadrophenia is more successfully operatic than many "official" operas of the same time, not least because it's a sophisticated fusion of art forms, primarily well-wrought music, with something powerful to communicate. Townshend reached his audience by writing about alienation; but his classical contemporaries, experiencing alienation themselves, frequently forgot their audience altogether.
Stockhausen's operas (such as Donnerstag aus Licht, 1978) are too navel-gazingly bizarre to expect much uptake. Michael Tippett, who wrote his own libretti, sometimes created psychological stories so convoluted that they can remain baffling even if you like the music.
But The Who's rock operas connect with a public wide enough to include classical-music journalists. We were all teenagers once. We've been there too, even if we were practising three instruments at the time. And we love good music, well performed, whatever its genre. Tommy and Quadrophenia are as characteristic of their era as any opera by Mozart or Wagner.
Labels can be deceptive. Quadrophenia may not be a traditional opera, but it's a marvellous band performing terrific music that tells a strong story, blending song, drama and spectacle in a manner of its own. Moved? Exhilarated? Uplifted? You bet. Rock opera? Yeah. Why not?
'The Who - Tommy and Quadrophenia Live with Special Guests' is released on 7 November by Warner Music Vision