It’s generally agreed that the late ’60s/early ’70s was an especially fertile period in rock music history, and perhaps the most provocative genre at the time was progressive rock (or “prog” among devotees), the dense, complex, lengthy, ambitious, lyrically puzzling music produced by a handful of British bands who strove to bring rock a degree of sophistication and critical respect.

I say prog rock was provocative because it truly provoked reaction.  It was a proud and radical departure from the three-minute mainstream rock, soul and pop songs that dominated the musical scene in the 1965-1977 period.  A huge, largely male demographic embraced it fully, spending hours under the headphones absorbing every nuance of these song suites and extended opuses, and religiously attended their concerts.  Others, though, turned up their noses, dismissing it as excessive and pretentious, and counter to the prevailing wisdom that “rock was and should remain tied to adolescence and youthful rebellion, not some medieval fairy tale,” as one writer put it.

Progressive rock is marked most prominently by:  virtuoso instrumental performances on keyboards, guitars and bass; ethereal, haunting vocals, sometimes with backing choirs;  sonically amazing production values; and mystical, surreal lyrics.  It is typically arranged in multi-part suites and extended tracks involving complex changes in keys, tempos, and time signatures.  These can stretch to 20 or 30 minutes or more, and the musicians say it can be extraordinarily difficult and challenging to learn and perform.  It also demands far more effort and focus on the part of the listener than many people are willing to make, but to those who do, the rewards can be high.

In the post-Sgt.Pepper period, rock had progressed to the point where the more adventurous musicians were eager to try new things, to push the boundaries, to employ classical and jazz instruments and structures in rock music, to abandon the three-minute pop song format in exchange for something weightier, longer, more complex.

These musicians, by and large, were British, raised at conservatories and colleges in Southern England with strong Anglican Church influence and a more serious approach to instrumental skills than was then typical of most rock bands.  Indeed, it was their considerable playing and composing talents (most notably on keyboards and guitars) that made so many young Americans sit up and take notice.  This was not music to dance to, they said, nor mindless pop to sing along to; this was meaty stuff that deserved our undivided attention.  “We find that people like listening to our albums alone, with candles lit,” said Genesis front man Peter Gabriel in 1974.  “It’s very escapist.  I personally think it’s a more satisfying way to hear music, being isolated.”  And it came along just as FM radio was beginning to play “album-oriented rock” formats, sometimes playing entire albums, or sides of albums.  For about five years or so, the two fed each other’s growth.

I did a little survey of some music loving friends to find out what they think of when they hear the term “progressive rock.”  Most responded along the lines of, “Stuff like Yes and Pink Floyd …you know, stoner bands.”  While the bulk of progressive rock’s listeners through the years have no doubt been regular weed smokers, interestingly, many of its most accomplished practitioners swear they rarely partake.  “The music we’re playing is complex and challenging,” said Martin Barre, longtime guitarist with Jethro Tull.  “It takes a lot of concentration.  You’ve got to keep your wits about you.”

There were roughly a dozen heavy hitters pumping out best-selling quality prog rock in its peak years (1971-1975):  Pink Floyd, Yes, Genesis, King Crimson, Emerson Lake & Palmer, Jethro Tull, The Moody Blues, Uriah Heep, Gentle Giant, Renaissance…  A few dozen more bands filled out the field, lesser known but avidly followed by a loyal fan base:  Camel, Hawkwind, Soft Machine, Caravan, Atomic Rooster, The Nice, Strawbs, Curved Air, Procol Harum, Supertramp…

Prog rock was pretty much exclusively a British export, with a few from Germany like Kraftwerk and Tangerine Dream, and Rush from Canada, but there were also a couple noteworthy American exceptions to the rule.  There are those who think Frank Zappa and The Mothers of Invention 1966 debut “Freak Out” was, in fact, the first progressive rock album ever made.  Zappa certainly experimented boldly with a broad array of styles, influences, instruments and genres throughout his 30-year career, as did Todd Rundgren, who has some dazzling prog rock tracks in his catalog, with and without his occasional band project, Utopia.

Also part of the picture were the bands — many of them American — who merely dabbled in prog rock.  They either began as prog but moved into hard pop rock (Journey, Kansas, Ambrosia, Styx) or used prog rock instruments and techniques in a pop song format (Electric Light Orchestra, Alan Parsons Project). Within the prog rock genre, there were specialties: a very theatrical sort of art rock was the calling card of Genesis; playing with symphony orchestras proved to be a breakthrough for The Moody Blues; spacey sound effects and lyrics about madness are found throughout the recordings of Pink Floyd; Elizabethan folk themes and soaring flute passages mark the memorable Jethro Tull tracks; hymn-like keyboard exercises dominate the oeuvre of Emerson Lake and Palmer.

A raft of intellectual, often ponderous subjects — romantic literature, medieval warfare, woodland folklore, the work of J.R.R. Tolkien, social class commentary, utopian morals, the Apocalypse, mental illness, spiritual transformation, the struggle between good and evil — have been explored in progressive rock lyrics.  Are they taking themselves too seriously?  Sure, sometimes.  Isn’t it a little too wordy and vague?  Undoubtedly.  And yet, it’s an important piece of the prog rock puzzle.  For avid listeners, the impenetrable lyrics are part of what make the genre interesting and open to repeated listenings and multiple interpretations.

Mythology and surrealism are favorite topics of prog rock lyricists, as shown in these examples:

“The keeper of the city keys put shutters on the dreams, I wait outside the pilgrim’s door with insufficient schemes, the black queen chants the funeral march, the cracked brass bells will ring, to summon back the fire witch to the court of the crimson king…” King Crimson, 1969

“Changed only for a sight of sound, the space agreed, between the picture of time behind the face of need, coming quickly to terms of all expression laid, emotions revealed as the ocean maid, all complete in the sight of seeds of life with you…” Yes, 1972

Even the album artwork played an important role.  Mesmerizing cover art, like those of artists Roger Dean and Barry Godber found on Yes’s and King Crimson’s LPs, could transport you into the parallel universes their songs were trying to describe.  Tull even concocted an elaborate 18-page newspaper parody as its cover for “Thick as a Brick,” poking fun at the whole notion of “concept albums.”

There’s a marvelous book called “Yes is the Answer” by Marc Weingarten, a collection of deep, subjective essays about progressive rock.  In his foreword, he cops to being a huge prog fan in his teens while cheerily confessing that the critics aren’t wrong in labeling it sometimes overblown, pretentious or self-indulgent.  “We would laugh at some passages, marvel at others,” he writes.  “When you’re a certain kind of cloistered 15-year-old male, you’re looking for music to lay out an alternate universe much the same way that Tolkien, weed and comic books did.  Prog delivered the goods like nothing else.”

Some point to Yes’s “Tales of Topographic Oceans” (1974) as the “jumping the shark” moment in progressive rock’s life arc.  It was a double album with only four songs — four 20-minute songs.  That’s asking a lot of anyone but the most diehard fans to tolerate.  Similarly, concerts had evolved into multimedia extravaganzas with rotating keyboard platforms, levitating drums and multiple costume changes.  It was all designed to add dynamic visuals to the experience but too often ended up an excessive overshadowing of the music.

By 1975 and the economic downturn in England, punk was born, a loud, fast and sweaty blast of hard rock that served as a slap in the face to the pomposity and intellectualism of prog rock.  Punk proponents vilified the progs for preposterously drawn-out material based on Herman Hesse’s “Siddhartha” (“Close to the Edge” by Yes), T.S. Eliot’s “The Waste Land” (“Selling England By the Pound” by Genesis) and George Orwell’s “Animal Farm” (“Animals” by Pink Floyd).  Punk didn’t last too long, but by exposing the sheer silliness and self-indulgence of much prog rock music, its audience began to dwindle.

Still, progressive rock has never really gone away.  There’s not only a devotion to those classic ’70s albums among the crowd that grew up with them, there has also been a sort of neo-prog movement going on under the radar for most of the past 30 years.  Bands like The Mars Volta and Tame Impala are producing work that certainly qualifies as a new generation of mind-expanding, barrier-breaking progressive rock.  It may not be the same prog rock music we’re speaking of here, but hey, if it shakes things up, shatters barriers, fuses disparate things in a new and pleasing way, I’m all ears.

To some ears, progressive rock may be tough to absorb, it may require repeated listenings to appreciate, it may not be everyone’s cup of tea, but you’ve got to admit it’s ambitious and often breathtaking in its artistry.  It challenges, it impresses, it compels you to dig deeper for further rewards, and if you’re receptive, you’re usually not going to be disappointed.

20 essential progressive rock albums:

Pink Floyd, “The Piper at the Gates of Dawn,” 1967

Moody Blues, “In Search of the Lost Chord,” 1968

King Crimson, “In the Court of the Crimson King,” 1969

Moody Blues, “A Question of Balance,” 1970

Genesis, “Nursery Cryme,” 1971

Emerson, Lake and Palmer, “Tarkus,” 1971

Yes, “Fragile,” 1972

Pink Floyd, “Meddle,” 1972

Jethro Tull, “Thick as a Brick,” 1972

Yes, “Close to the Edge,” 1972

Genesis, “Selling England By the Pound,” 1973

Pink Floyd, “Dark Side of the Moon,” 1973

Emerson Lake & Palmer, “Brain Salad Surgery,” 1973

Jethro Tull, “A Passion Play,” 1973

Genesis, “The Lamb Lies Down on Broadway,” 1974

Renaissance, “Scheherazade and Other Stories,” 1975

Kraftwerk, “Autobahn,” 1975

Rush, “2112,” 1976

Pink Floyd, “Animals,” 1977

Pink Floyd, “The Wall,” 1979