Inexplicably ignored by the Rock and Roll Hall of Fame, Britain's Jethro Tull made some of most innovative and sublime music of its generation. And Ian Anderson, from Day One the singing, songwriting and flute-playing centerpiece of all things Tull, has never stopped making music, despite the fact that his band will celebrate its 50th anniversary in 2017.

This week, Anderson releases a solo project, Homo Erraticus, that recalls that brief-but-successful period (1972 and ’73) when Jethro Tull was making “prog” (progressive) records alongside the noodling likes of Yes and Emerson, Lake and Palmer. Anderson, of course, quickly moved past those so-called concept albums (Thick As a Brick and A Passion Play) to make more conventional (for him, anyway) Tull records.

This one follows 2012’s Thick As a Brick 2, which found Anderson writing, tongue once again in cheek, in the guise of Gerald Bostock, a character he’d created for the original TAAB. Then, Bostock was presented as a cynical 10-year-old poet. For the sequel, he’d grown up (as, presumably, has Anderson) but remained rather prickly.

The fictional Mr. B “returns” for Homo Erraticus, which offers a themed series of songs —very “proggy,” as the English say—describing the various ages of man.

All of this raises the question, what then of Jethro Tull? Although Anderson has been the only constant through many personnel changes over the years, he was always been quick to point out that Jethro Tull, the band, was a separate entity entirely. Particularly crucial were the playing talents of lead guitarist Martin Barre, who took his place at Anderson’s side in 1969, for the second Tull album, and never left.

To bring you up to date, Jethro Tull hasn’t made an album of new material since 1999, the market for such things not being what it once was. Touring has long been the band’s bread and butter, with Anderson, Barre and an evolving cast of characters revisiting “Aqualung,” “Living in the Past,” “Locomotive Breath” and “Skating Away” for dedicated and adoring crowds everywhere.

Barre has of late been openly critical of Anderson’s “safe” song choices for Tull tours, and has started a band called New Day, which focuses on “deep cuts” for the hardcore fans. As for Anderson ...

You used to make fun of prog rock, and concept albums. Onstage.

Ian Anderson: Jethro Tull, we did that in '72 and '73, we were deliberately courting that disaster which became prog by making a little fun of it, in the case of Thick As a Brick. In the case of A Passion Play, my guilt was that I took it all a bit seriously and thought "Maybe we should really be playing this kind of thing. Maybe that should be our calling card." Because Thick As a Brick had been so hugely successful, having begun as being a bit more satirical. A bit more of a pastiche, in terms of the concept. The music behind it, of course, was often quite serious and quite dark.

It’s not something that over the years I felt I wanted to dwell on overly, but we’ve always continued to play excerpts from Thick As a Brick since then.

So why is Homo Erraticus a concept album?

IA: After the TAAB2 piece, which was very much written as a 40-year sequel to Thick As a Brick 1, I thought "Well, I'm not going to make a trilogy here, but let me have a little bit of continuity with Gerald Bostock coming back to write lyrics again." That was already in my head in late 2012. To be precise, at 9 o'clock in the morning on January the 1st, 2013, I set myself the very deliberate challenge of beginning to write an album. And very specifically, from an empty head, from having no preconceived bits stashed away. It was literally going from a clean sheet and seeing what happened. That evolved, over the next couple of days, into the first track, "Doggerland." Very quickly I then started to say "Where is this taking me?" On Day Two, I probably had the bullet points of the elements that would be the rest of the album. Then I had to develop those into real music and lyrics.

It was always the intention that it would be a rather rocky album, rather than so much acoustic music. That’s the way I wanted it to turn out, and I deliberately played acoustic guitar only in a couple of places. But of course, all the music was written with the acoustic guitar and the flute. All the demos were made on a laptop in a hotel room, strumming a treble guitar and singing very quietly so as not to disturb the other guests.

You’ve been performing as the Ian Anderson Band for several years now. Is this more satisfying for you than the latter-day Tull concerts?

IA: For me, the name means nothing at all, whether it's Jethro Tull or Ian Anderson. I'm still singing my songs and playing my music. Nothing changes, except there are some personnel differences. And that's the nub of the issue. That's the question that I suppose has to be asked. It's not about solo albums versus Jethro Tull albums. To me, there's no difference. It's just me turning up for another day at the office, really.

Doane Perry, who’d been our American drummer since ’84, ’85, he was in the band for a long time. Whenever it was major tours in Europe or the USA, he’d be the drummer. For the odd show, or whenever Doane sometimes was not feeling terribly well, someone else would be the drummer. Just as Martin Barre once or twice, or three or four times, was not always the guitar player when he wasn’t feeling terribly well, or didn’t want to go to a particular exotic location where he thought he might get food poisoning. But most of the time, those two guys were in the band.

In deference to those two—apart from the 26 other ones who were also in Jethro Tull over the years—I just felt that maybe we should just leave this Jethro Tull description out of it, and it’s just me carrying on until I can’t do it any more. Using my own name, rather than the Tull name.

I say in the album artwork, this is a Jethro Tull album in all but name. That comes from people who’ve heard it saying “As soon as I heard the opening bars, I knew it was a Jethro Tull album,” then saying “Oops” when they’ve realized what they said. Of course it’s going to sound the same, because it’s me.

Is there still a Jethro Tull?

IA: There are essentially three Jethro Tulls. There's Jethro Tull, the 18th-century agriculturalist, If you Google the name Jethro Tull, you'll see him in there. I think he's currently Number Three. The other nine are me, and the band Jethro Tull.

There’s Jethro Tull, that vast repertoire of music released under the name Jethro Tull, through 2005-ish. And there’s Jethro Tull, the 28 members of Jethro Tull over the years who’ve been in the band. Obviously me, but under that band identity, many other people. All the members of the band I currently play with have performed as members of, simply, Jethro Tull.

So the question is, really, am I gonna play with Martin again? There’s no reason that won’t happen, it’s just that it’s not something that’s currently scheduled to result in a concert or tours in the next 12 months. Because I know what I’m doing for the next 12 months, and I’m sure Martin does as well.

He said some unkind things about you.

IA: I don't pay any attention to that. When I talk about Martin, it might sometimes be with a little frustration, in that he left it so long in his life to do the things I tried to suggest to him he ought to have done 10 years ago. Martin for a long time was just following his own pattern of doing the odd little bit of solo stuff. He made a few records and did the odd few dates, but he never really got to grips with it until two years ago.

In June 2011 I had a meeting with Martin and Doane Perry, about the future, and I said “Good time to start thinking about other options.” In Doane’s case, it was going to be inevitable because of health issues. He’s long been entertaining some fairly serious surgery, which was going to take him out of action for many months. He limps along, literally, and I think he’s happy doing what he’s doing.

Not to flog a dead horse, but there are loads of people who love and follow you, and they’ll say if it’s not Ian and Martin, it’s not Jethro Tull.

IA: Well, they're in absolutely safe territory, because it's not Jethro Tull right now. I'm busy doing stuff under my own name, and so is Martin. But that doesn't mean that we won't work again and call it Jethro Tull in the future. Or it might be Anderson, Barre and Palmer! Who knows?

People want to think that relationships like that go on forever, and unwaveringly to the bitter end. But life is too short, you know? I think it’s very important that people do try other things and play with other people. I know for a fact Martin’s having a great time doing what he’s doing. I’m so pleased that he is actually doing it. He has revolving door of musicians playing in his own band, and plans to do this, that and whatever.

This issue of solo-versus-whatever is, to me, kind of missing the point. The music, ultimately, is what people like. If they want you to stay married forever, I can only suggest they direct themselves to the 50 percent likelihood that their own marriages will fail. That seems to be the international statistic in the western world. Going on for a lifetime, most of a lifetime or half a lifetime, is something to feel—as I do—really good about. I don’t feel bad about it.

And I certainly don’t put behind me the possibility or even the likelihood that Martin and I will be on the stage together sometime before we actually can’t do it any more.