Byron Wien and Jeremy Siegel both say stocks are headed higher. But while Wien says that the Federal Reserve's quantitative easing policies have been a big part of the market's bull run, Siegel believes that the effect of the Fed has been badly overstated.
"I think a large part of the appreciation in the market this year is a result of Federal Reserve monetary accommodation," said Wien, the vice chair of Blackstone Advisory Partners. "That's what drove the market. It drove stock prices higher, and it kept interest rates low."
(Read more: Byron Wien: Why I've become bullish on the market)
But Siegel, professor of finance at the Wharton School and one of the best-known market bulls, takes issue with that characterization.
"I have to disagree with you here," Siegel directly told Wien on Thursday's episode of "Futures Now." "I think that one of the biggest myths on Wall Street is that it's QE that's driving the market."
"I'm looking at the earnings and the interest rate and saying, 'I can certainly justify these prices without having to resort to QE,' " Siegel continued.
(Read more: You're wrong—QE has not boosted stocks: McKinsey)
Because he doesn't think the Fed's $85 billion-per-month bond-buying program has been the main driver behind stocks, he doesn't think that a reduction, or tapering, of that program will have a traumatic impact on the market.