There aren't many things we can really count on in life, but during the '70s, you could pretty much bank on a new Chicago record every year — and expect to see it at or near the top of the charts. Chicago X was no exception.

The group had certainly struggled with the demands of its massive success in recent years, but they entered the studio to record Chicago X on something of a creative upswing. Singer/keyboardist Robert Lamm had shouldered much of the songwriting burden for their early LPs, but as time wore on — and he found it more difficult to keep up with the constant demands for new product — other members of the band stepped up.

By the time they entered the studio in the fall of 1975, Chicago had settled into a rough democracy with room for five or six songwriters on a record, helping keep things fresh even after years of steady touring and recording.

In time, certain members of the lineup would come to feel that the everyone's-a-songwriter approach worked to the band's detriment, but for Chicago X, it kept the multi-platinum machine running at a time when Chicago were still truly more than the sum of its parts. Lamm contributed four songs to the LP, trumpeter Lee Loughnane added one and two each came from guitarist Terry Kath, bassist Peter Cetera and trombonist James Pankow, adding up to an eclectic set that also managed to present a fairly clear picture of each member's strengths.

Still, for fans who'd been with Chicago from the beginning, it was clear that their time in the spotlight had taken a toll. Chicago X may have arrived on June 14, 1976 with a little more spark and overall energy than you might expect from a group that had been on the road for a decade, but it lacked the compositional depth and musical muscle they'd shown earlier in their career. It was essentially a pop album — not a bad one, outside the somewhat lyrically dunderheaded "Skin Tight" and "You Get It Up," but one that couldn't help but feel a little light when held up against the double-LP sets of years past.

Listen to Chicago Perform 'Once or Twice'

On the other hand, if their ability to stretch musically had earned them a hardcore following, it was the commercial component of their sound that made them a household name. The die had already been cast with a series of radio-friendly singles, many of which featured Cetera's distinctive lead vocals.

Cetera was riding a particularly hot streak when Chicago X came out, having been at the mic for a string of major hits — "Feelin' Stronger Every Day," "Just You 'n' Me," "(I've Been) Searchin' So Long" and "Call on Me" — that helped define the band's sound for the mainstream audience. To the group's increasing chagrin, Cetera's flair for pop balladry made his songs the natural choice for singles.

That approach would eventually come to impact Chicago's creative dynamic in some major ways, not all of them positive. But it paid major commercial dividends with Chicago X, which arrived at a time when the group's sales profile outside the U.S. had dipped.

Any new music was also threatened to be overshadowed by the release of their first greatest-hits record, which had topped the charts the previous fall. Their label needed a fail-safe single to keep record sales coming, and they found it in Cetera's gentle, strings-laden "If You Leave Me Now."

In later years, the band members would insist that "If You Leave Me Now" almost didn't make the album, describing it as a song they finished at the last minute in order to round out the track listing. The placeholder bass and acoustic guitar parts recorded by producer James William Guercio ended up on the final recording — and woodwinds player Walter Parazaider later admitted he was so unfamiliar with the end result that he thought he was listening to a new Paul McCartney single the first time he heard it on the radio.

Listen to Chicago Perform 'If You Leave Me Now'

However it came together in the studio, "If You Leave Me Now" ended up becoming one of Chicago's biggest hits. The single topped the charts on either side of the Atlantic — their first to do so. It also spurred Chicago X to double-platinum sales while giving the band its first charting LP in the U.K. since Chicago V.

The debate over Cetera's influence on the group continued for decades, but as far as the record-buying public was concerned, the verdict was obvious.

Chicago would soon face far bigger problems than which songs were chosen for singles. They'd make it through another tour and album, releasing Chicago XI (featuring yet another Cetera hit, "Baby, What a Big Surprise") the following fall, but in early 1978, Kath was killed after accidentally shooting himself.

His absence opened an emotional and creative void that sent the band toppling off its axis — but even if he'd lived, it's hard not to wonder whether Chicago would have found a way to continue the original lineup's winning streak.

"To be sure, the ballad-ness that the band became identified with through the singles after 'If You Leave Me Now,' that drove me crazy," Lamm recalled in the liner notes to the band's Group Portrait box set in 1991. "I know it drove Terry crazy, because that isn't what we set out to be and it isn't how we heard ourselves. It's still not how we think of ourselves."

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