In 1968, the Beatles had existed in the American public consciousness for just four years. Even Elvis Presley, who launched a major comeback that year, had been a national presence for just 12 years.

As such, that a mere rock 'n' roll band could exist — albeit in a greatly altered state, personnel-wise — for 50 years was simply inconceivable. After all, the musical genre that defined a generation was still, to some degree, in the "it's just a fad" stage.

But here we are in 2018 and Jethro Tull, which was named for the 18th-century inventor of farming implements, remains in business. Of course, it exists today primarily as the vehicle by which composer/lead singer/flautist/acoustic guitarist Ian Anderson — the groundbreaking group's sole remaining original member still touring under the Tull banner — recreates the band's singular music, which blends classic hard rock with everything from classical, jazz, and blues to pastoral British folk and third world motifs.

It's a blueprint that has yielded such classic-rock staples as the 1972 progressive-rock touchstone Thick as A Brick, "Bouree" (an adaptation of a J.S. Bach piece that Anderson has characterized as "cheesy cocktail jazz"), and two songs from the band's 1971 best-selling album, Aqualung, "Locomotive Breath" and the title track.

Despite his oft-professed distaste for the marking of milestones, Anderson, 71, is devoting this year to celebrating Jethro Tull's half-century of music-making, with the three-CD 50 for 50 boxed set, and a victory lap around North America that on Saturday, Sept. 8, brings his program, "Ian Anderson Presents Jethro Tull, the 50th Anniversary Tour" to the Mann Center for the Performing Arts.

During a recent phone call, Anderson, who is seldom — if ever — at a loss for words, covered such topics as Tull's earliest days, the absence of  flute in his most famous song, and why Tull didn't play Woodstock.

Take us back to the first time the original quartet — you, guitarist Mick Abrahams, bassist Glenn Cornick, and drummer Clive Bunker — got together.

It was in December of 1967, and we were in a school … somewhere in [the British towns of] Luton or Dunstable. Essentially, there was a little bit of common ground over 12-bar blues, and so we thought … the logical starting point was to play blues covers.

When did original songs enter the picture?

In those first few weeks, I started to [co-write with the band members] some songs in that style. Glenn and Clive had played together in a previous band or two, and Glenn and I had played up in the north of England with the John Evan Band [keyboardist Evan joined Tull in 1971]. So, it was kind of "two-plus-two," a fusion, essentially, of parts of two different bands.

You are universally acknowledged as the man who made the flute a rock ’n’roll instrument. Yet, “Aqualung,” the song for which the band is arguably best-known, doesn’t have a flute in it. Do you find that ironic?

It certainly is. I remember writing the song sitting in a hotel room somewhere with Glenn Cornick and coming up with the riff and chord sequences — at that point there were no lyrics. I was just playing it on an acoustic guitar, and then had to convey the essence of it to [second Tull lead guitarist Martin Barre]. I always intended it to be a loud electric guitar riff.

Sure, I could have made it a flute riff, but it seemed to fit the electric guitar. So I never added any flute parts because, of course, elsewhere in the song, I'm strumming the acoustic guitar, at least in all the quieter passages.

That is, indeed, the best-known Jethro Tull song, and it doesn't include the flute. So, yes, it is a quirky one. But I've more than made up for it. I came off stage in Florence, Italy a couple of nights ago and said, 'My God, these poor people, having to sit there for nearly two hours of penetrating, excruciating loud flute. It must drive them mad. I couldn't cope with it.'

Are there Tull songs you thought should have achieved the status of “Aqualung” but didn’t?

There are certainly lots and lots of songs that would be amongst my personal favorites from a musical standpoint that may not necessarily be those that have set the world alight elsewhere. For instance, on the Aqualung album, the song "My God" is one that I think is one of the important songs that I've written. On the Crest of a Knave album, the song "Budapest" is, I think, a very encompassing piece of music that does give a lot of the nuances of Jethro Tull in its eclectic stylings over the years.

Speaking of 50th anniversaries, next year will mark that of the Woodstock festival. Jethro Tull won’t be part of any  celebration because the band declined the invitation to play there. Why?

It was I, not the band's management, that declined the invitation.

It was relatively short notice, and we were on our second American tour at the time, and our second album, Stand Up, had just gone to No. 1 on the charts in the U.K., and I was very much aware that this album was the more eclectic beginnings of Jethro Tull in a more creative sense.

It really needed time to establish us, and I really felt at that point, in the middle of 1969, we were not really fully formed, we were learning our craft, we were learning our skills as performers and I was learning my job as a songwriter and performer, so it was just too early to be putting a stamp on something that was set to become a huge, epic festival.

Our early label-mates on Chrysalis Records was a band called Ten Years After. Ten Years After went to play Woodstock and were one of the hits of the festival. It took them from almost obscurity to being a household name throughout the world.

Ten Years After were playing at some German festival a few years back and I went over to Leo Lyons, who was still in the band at that time. And I noticed stuck on to the edge of his bass guitar there was a set list. I said, 'What songs were you doing?' And he said, 'Oh, the usual ones.' I said, 'That set list looks like it's been there a long time.' He said, 'This is the set list from Woodstock.' So that's what they were still playing some 40 years later.

I would find that somewhat limiting, to be known just for these very few pieces of music and for a very definitive style of music. In a way, that was a curse. They were never really able to move on from forever being associated with Woodstock.

It was certainly one of my best career decisions not to do Woodstock.

MUSIC

Jethro Tull

  • 8 p.m. Saturday, Mann Music Center for the Performing Arts, 5201 Parkside Ave., $39.50-129.50, manncenter.org