The index could be up about 10 percent or down 10 percent this year, said James Paulsen, chief investment strategist at Wells Capital Management. "We're going to be in a broad trading range this year," he said Monday on CNBC.
In a "Squawk Box" interview, he said he's ultimately betting on a flat 2015. "We might see over 2,220 [or] 2,250 this year. We might also see 1,850."
Those views put Paulsen in the popular, cautious crowd among Wall Street watchers calling for slim gains and broad consolidation for the year ahead, after the S&P delivered double-digit gains in 2014, finishing at 2,058.
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"We have a more vulnerable market. I'm not saying it wouldn't go higher over the next few years. I think it's going to. But we have a market at 18 times earnings, sentiment is the calmest … it's ever been," Paulsen said.
He added the stock market is caught between two opposing forces.
"We've got much better [economic] growth ... 3.5 percent, maybe up towards 4 percent this year ... the best growth of the recovery," he said. "But we are also near full employment and are very close to setting off inflationary indicators, which I think will be problematic for the markets."
Last month, Paulsen, who had ridden the rally higher over the years, said he's going "underweight" U.S. stocks for 2015.
He further explained his position Monday: "We may melt up on better economic growth or melt down on bond vigilantes and the Fed having to reset rates during the year."
"We have to do one thing: ... Reconnect interest rates in the United States to the economic cycle. We can no longer have interest rate prices on fear … when the economy is growing like this," he added.
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In contrast, Jack Ablin, chief investment officer at BMO Private Bank, told CNBC on Friday that stocks can move higher in 2015, perhaps into bubble territory—kind of like the late 1990s.
Ablin's call follows a similar prediction from billionaire hedge fund manager David Tepper last month. The Appaloosa Management boss said "enjoy the ride" but be wary of overvaluation.