As most songwriters can attest, there often comes a point in the writing process where something stalls.

In 1970, Chicago's Robert Lamm, one of the group's primary songwriters in the early years, realized that perhaps there was a whole other song itself in that creative obstruction. The result, "25 or 6 to 4," became one of the band's best known hits.

"It’s a reference to time," he said of the track in 2009. "It’s a song about writing the song. I looked at my watch while I was writing, and it was 25 minutes to four in the morning or maybe 26."

With an intriguing and somewhat puzzling title, the song was often perceived as a reference to some sort of drug activity. The single was even banned in Singapore entirely in 1970 for its "alleged allusion to drugs." "Some of the guys in Earth, Wind & Fire say to me, 'I know you were doing acid when you wrote that song!'" Lamm explained. "Of course, I said, 'No, no, you’ve got it wrong.' Though it was the acid era."

Watch Chicago Play '25 or 6 to 4' Live in 1970

Still, Lamm knew the tune would need the input of his bandmates to round out the track. "Most songs that were written, especially in the early days, whenever I got them to the band and we started rehearsing them, that's when the songs took shape - once these guys got hold of them," he said on The Chris Isaak Hour. "There was definitely a lot of raw material. I thought it was a song when I wrote the words down, I wrote the changes down and I brought the charts to rehearsal, but it wasn't really a song until they all played it."

"25 or 6 to 4" began to really fall into place once guitarist Terry Kath laid down a blistering, distorted solo. Kath, who died in 1978 at age 31 from an accidental self-inflicted gunshot wound, had made a significant impression as a skillful guitarist during his tenure with Chicago. Among his fans: Jimi Hendrix.

“People say a lot of things about Chicago,” Matchbox Twenty's Rob Thomas said as he inducted Chicago into the Rock & Roll Hall of Fame in 2016. “And I know that ‘badass’ generally is not one of them, but just remember that when Jimi Hendrix met them for the first time, he told them that their horn section sounded like one set of lungs and their guitar player Terry [Kath] was better than him. That, kids, is badass."

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