This is typically the worst month of the year for stocks, but August turned out to be so awful that perhaps some small flicker of light should have been expected. Besides, the Dow has had a winning September for four of the last five years (August is usually a plus month). From the WSJ:

Not everyone was convinced by Wednesday's bump. Some noted that volumes remain weak, stripping the day's gains of much of its significance. Recent sharp movements amid conflicting economic data could foreshadow a month of steep drops and heightened volatility, said Jim Paulsen, chief investment strategist at Wells Capital Management. "Normally at this point in the cycle, you're debating whether we get 3% GDP growth or 1.5% growth. This time, it's 3% or a depression, and that type of debate really sets us up for some potentially violent moves in bond yields and stocks, depending on how that works out," Mr. Paulsen said. "We got a flavor of that today."