As Chicago celebrates its 50th anniversary this year, the band is flying high with an induction into Rock and Roll Hall of Fame in 2016, and a place among the 2017 Songwriters Hall of Fame class. Founding member Jimmy Pankow, the songwriter and trombone virtuoso who's responsible for threading Chicago's signature horns throughout five decades of music, spoke with Billboard about his writing process, the surprising story behind one of Chicago's most cherished love songs and why the band won't retire from touring any time soon.

Pankow will join the SHOF 2017 class at a celebration on June 15 along with fellow Chicago bandmate Robert Lamm, Kenneth "Babyface" Edmonds, Berry Gordy, Jay Z, Max Martin, and Jimmy Jam and Terry Lewis of The Time. Also to be honored at the June 15 celebration are Ed Sheeran, Alan Menken, Caroline Bienstock and Pitbull.

You were the lead architect on many of the band's hits. Can you share the story behind one of them?

Yeah, I've got a good one, "Just You 'n' Me." This is a song dealing with a former relationship. We had had a huge fight, it was a nasty lovers' quarrel, if you will. She locked herself in the bathroom and wouldn't come out; she was crying hysterically. I was asked to leave, she never wanted to see me again. I said, "Open the bathroom door, we have to talk. You can't lock yourself in the bathroom all day. I'm going to count to 10 and I'm going to come through the door." I counted to 10 and she didn't open the door, so I busted through the door. And I saw the look on her face and it was so terrifying it freaked me out as well, and I backed out of the bathroom and I turned my head and saw my piano down the hall and I went right to the piano and sat down and "You are my love and my life, you are my inspiration" came out of me. "Just You 'n' Me" poured out of me in its entirety. Usually when I write songs I come up with an idea for a chorus or a hook and fill in the blanks in stages. This was a moment of clarity I've never experienced before or after. It remains a special event in my songwriting experience.

There are so many facets to a Chicago song. What's the band's songwriting process been like through the years?

It's very organic. Somebody will come up with a song and we'll pass it along and throw ideas into it and it will come to fruition. My job has been, for all these years, to sketch out an approach for the horn section. But in terms of my own songs, inspiration is a constant thing. You can be inspired with an idea in any given moment. There have also been songs in my catalog that are instrumentally challenging for the band and for the horn section, and I enjoy that as well.

That horn section… it's Chicago's signature.

When we put the band together we basically were talking about a rock n' roll band with this horn section and we said, "What are we going to do with that horn section that makes it a main character in a song?" And that really is a big part of our signature. If you take the horn section out of the songs, it's still Chicago because of the people performing it, but that horn section is an ID, it's a trademark. I took a melodic lead-voice approach to our horns, where the horn section becomes another lead vocal and interweaves in and around the actual vocals and becomes a part of the story of the song.

How hard is it to play those trombone parts year after year, show after show?

It didn't dawn on me when I wrote this stuff -- we'd be in the studio writing two songs a day sometimes -- and it never dawned on me that we'd be playing all these songs back to back in concert for two and a half hours. So at the end of the show your lips feel like you were just in the ring with Muhammad Ali. When I have a very important personal event I need to be present for, I call in my stunt double. His name is Nick Lane, and he's a very fine trombone player from L.A. And when he goes out for a couple dates in my absences he always calls me and says, "Jimmy, no matter how much I practice at home this show is the toughest show I've played." It's an honest assessment. The horns are playing in every part of the damn song.

Chicago just celebrated its 50th anniversary. That's a remarkable number, with a remarkable number of dates clocked on the road.

Recording is still something we do. We have a mobile rig -- the technology has made it easy to record in hotel rooms, backstage, on the tour bus. But the live performance is your connection with the audience, that's what puts you on the map. There's too many artists that don't understand that without everyday people that spend their hard-earned money on those tickets, you wouldn't amount to anything. An audience is what gives you credibility. Picasso wouldn't be Picasso without an audience for his art. So when you get on stage and you get that approval of a crowd, it's amazing. And it's amazing every night. I'll never get sick of it. There are nights I go on stage with 103 fever and come off feeing like Superman because of the adrenaline of the audience. When you look out at the crowd you can see them relating to that moment in their lives that this music resonates with, and they come back every year to relive those moments with the band, live. We're going to do it until we can't do it anymore. It's pretty cool to be celebrating the 50th anniversary. Where do you go from here?

Good question. What is next for Chicago?

There's a few really cool possibilities for the next chapter for Chicago that I'm not at liberty to discuss at the moment. But on a personal note, I've begun to reach out and put the word out that I'm available to do other projects and I'm starting to become busy with outside projects as well. A trombone player in guitar-land is kind of a fish out of water, but guess what? I'm discovering there are amazing musicians of all genres here. There's jazz going on, there's pop going on, there's classical, rockabilly, you name it. The songwriting process is ongoing. To get back to Picasso, maybe I'll die with a drafting pencil in my hand as I'm writing that last song. And that would be would be a good way to go, with my boots on. And the band continues to evolve, too. New music is being discussed as we speak.