"When it comes to volume, be careful what you wish for. A common criticism of the bull market in recent years is that buyers do not have a lot of conviction because volume has not been strong. The implication has been if volume does not pick up, the market may decline. However, the past few years show the opposite: that markets climb on relatively quiet trading for long stretches of time and then briefly pull back as volume jumps," he wrote.
The fast decline in stocks has also led to lots of chatter about whether the market would decline 10 percent, widely viewed as "correction" territory, or even signal the onset of a bear market. The market has not fallen more than 10 percent since 2011, though it fell 9.8 percent in 2012. It is viewed as a bear market when the market falls 20 percent.
While 10 percent is often referred to as correction territory, Art Cashin, director of floor operations at UBS, said he does not think it necessarily designates a correction. "Over the years, I don't think that was anything I was taught," he said. "What is wrong with saying the market has a 7 percent correction. A correction is a pullback that is not converted to a bear market."
Paul Hickey, co-founder of Bespoke, agrees that the 10 percent number is a bit arbitrary. "You look at the numbers. When you have a 10 percent correction, the average decline is 15 or 16 percent," he said.
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Jeff Hirsch, publisher of Stock Traders's Almanac, also says it's not that simple.
"20 percent is pretty much the unwritten rule, which is fair enough. Anywhere in the 15 to 20 percent is bear market territory but a correction can be 1 or 5 percent," he said. "10 percent is where people get itchy."
"If we are down somewhere around 20 percent at any juncture you'd have to consider seriously it was a bear market, unless it was a flash crash kind of thing and it was intraday," he added.
Bear markets could also be short lived. "We had a 45-day bear market in 1998," he said.
Hirsch said Ned Davis Research defines bear markets very specifically:
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According to the Stock Trader's Alamanc, Ned Davis view is that: "A bear market requires a 30 percent drop in the Dow Jones Industrial Average after 50 calendar days or 13 percent decline after 145 calendar days. Reversals of 30 percent in the Value Line Geometric Index since 1965 also qualify."
—By CNBC's Patti Domm. Follow her on Twitter @pattidomm.