Singer/keyboardist Robert Lamm has been part of a particular band of brothers for decades as Chicago, the group he co-founded, celebrates its 50th anniversary this year.  But just before the band’s latest summer tour hits Houston this Sunday (with co-headliners the Doobie Brothers), he’ll be inducted into another elite group: The Songwriters Hall of Fame, going in with a class that also includes his Chicago bandmate/trombonist James Pankow.

The pair found out about the honor last year, about the same time they were notified of the band’s (long) overdue induction into the Rock and Roll Hall of Fame. Lamm’s reaction, though, is a bit surprising.

“I’m a little ambivalent about it to be honest. I’m flattered, I never thought it would be bestowed on me. Some of the writers of the greatest American songs like Cole Porter, the Gershwins, and Burt Bacharach are in there,” Lamm offers. “But to a large degree, it’s for the very earliest work I did on the first dozen or songs I composed for Chicago. That was a long time ago. I didn’t know what I was doing then, but I know what I’m doing now!”

Still, it’s hard to argue when some of the band’s Lamm-penned (and usually sang) tunes include classic-rock and marching-band staples like “Saturday in the Park,” “Does Anybody Really Know What Time It Is?” “Beginnings,” “Questions 67 & 68”, “Dialogue (Parts I and II),” “Another Rainy Day In New York City,” and “Harry Truman.”

But it’s another numerically-inclined song – with its title literally inspired by the time of the morning that Lamm wrote it – that has been such a calling card that the band recorded it twice: “25 or 6 to 4.”

Lamm says there was one incident shortly after the tune came out that made him think it was something bigger than just a hit. “I do remember going to a dinner party a couple of years after it came out, and Ringo Starr and Harry Nilsson were there and another big performer whose name I can’t remember, and they were all talking about the song,” he recalls. “That’s when I realized there was something [extra]. And it’s been sampled a number of times by hip-hop and rap artists and been in movies. So that all adds up to it having more impact than I ever expected.”

For years, the three most egregious exclusions from the Rock and Roll Hall of Fame were Yes, Deep Purple, and Chicago. With all three acts entering in the past two years, Lamm’s frequent — and current — tourmates in the Doobie Brothers now occupy that short list.

“Their time will come, I know it,” Lamm says. “I love those guys, and we’ve worked with them a lot; we have a long history. Our tours are very successful and are really a joyous event. It’s music that has meant so much to multiple generations. And the staying power of their music along with ours performed in one evening is something. And they are professionals.”

For their current summer tour, Lamm promises a more “updated visual aspect” to the show, specifically for outdoor venues. As well as a set-balancing list of the big hits (including those originally written and sung by long-departed bassist Peter Cetera), alongside some deeper cuts for the hardcore fans, and different list from their previous tour.

And he says the band is not just tripping down memory lane. Lamm also promises a surprise in that one song played will be “a nod to EDM music,” as he notes in recent years an older remixed Chicago track has become an unlikely dance club hit (their 1979 song “Street Player”).

Finally, coming out in August is a Steven Wilson-remixed version of 1970's Chicago II. The white-hot, prog-leaning Wilson has done similar work for Jethro Tull reissues, and has a solo career along with his band Porcupine Tree. Lamm adds that the band is contemplating playing that entire double album in concert down the road.

“I never thought that it could sound better than the original release, but it’s really something very different, and it’s great what he’s done,” Lamm says. “I haven’t listened to any of those songs in decades!”

In fact, there has been so much new activity in the Chicago story recently, that the ending of last year’s career-spanning CNN documentary, Now More Than Ever: The History of Chicago had to be continually re-edited.

Lamm was happy with the result, though it was not without controversy in that it was produced by the nephew of a current band member. Ousted original drummer Danny Seraphine says he wasn’t represented well, and it did not include reflections from  Peter Cetera or original producer/manager James William Guercio, both of whom declined to participate in the project (as did keyboardist Bill Champlin). Aside from Lamm, the other co-founders still in the group are Pankow, Lee Loughnane, and (sometimes) Walt Parazadier.

As for Texas, Lamm notes the band has “probably played Texas 50 times in 50 years, starting when we used to open for Jimi Hendrix.” And he’s recently visited Marfa and Big Bend at the behest of his wife, a painter/sculptor who admired the natural light of the region.

He’s also celebrating the release of Time Chill, a retrospective anthology of his solo career since the early ‘90s with some unreleased and remixed material. So, while Lamm and Chicago are happy to revisit their past for big audiences on tour, they are not beholden to it.

“We’re not thinking about the 50 years behind us,” Lamm sums up. “We’re thinking about what’s ahead and all the new projects we are going to attempt!”

Chicago and the Doobie Brothers perform Sunday, June 18 at Cynthia Woods Mitchell Pavilion, 2005 Lake Robbins Dr., The Woodlands. Gates open at 6:30 p.m.; $30-$140.