That's a question wary investors have been asking for a while, and they now have another reason to be concerned.
A survey conducted by Bespoke Investment Group shows that 68 percent of those surveyed believe the S&P 500 will be up one month from now. That's the highest number the poll has ever seen.
On the surface, this seems like good news. Stocks have rebounded to record highs after a sharp selloff last month, and investors are naturally bullish. But could the positive vibes be too much of a good thing?
"There are way too many bulls right now," said Gina Sanchez, founder of Chantico Global. "Everybody is calling for the next big bull run. To me, that's unsustainable."
According to Sanchez, a CNBC contributor, the math doesn't add up to the fundamental case for a bull market. She says that the S&P 500's growth has compounded well above the expected nominal GDP growth rate plus dividend yield.
The current dividend yield on the S&P 500 is 2 percent while the IMF forecasts 2014's GDP growth to be 2.2 percent. However, the S&P 500 is up 9.5 percent year-to-date.
"There has to be a relationship," Sanchez explained. "Over time, that will come back into line. The question is how and when."
But that doesn't mean the S&P 500 won't move higher despite the lack of a fundamental basis, she said. Given fairly low interest rates–the benchmark U.S. Treasury 10-year bond is under 2.4 percent–the hurdle rate for equities is relatively low. Institutions seeking yields are attracted to stocks, adding "excess liquidity" that will keep a bid on equities, said Sanchez.
"While these are reasons that equities are the only game in town, we must remember that the game is being rigged by central banks," she said. "That doesn't mean equities are necessarily a good fundamental buy. They are not."
Mark Newton, chief technical analyst at Greywolf Execution Partners, believes the technicals agree with Sanchez. "Sentiment has shifted from bearish to bullish a lot more quickly than any of us expected," he said. "But none of these issues that we were all worrying about have been solved."
Though Newton's chart of the recent price moves in the S&P 500 show the index is above its August lows and broke through a September downtrend, it may not be enough to be encouraging.
"The highs made in September were just barely above the levels that were reached back in July before we faded," Newton said.
Newton sees a short-term cap on the S&P 500 somewhere between 2,030 and 2,040. "We need to consolidate some of these gains after the election, and that would probably set up for a better area to buy dips heading into year-end," he said. "But it's tough when sentiment moves too dramatically in the opposite direction very quickly without any good reason."