The stock market could soon drop another 8 percent, but it's still a bull market, the editor and publisher of "The Gartman Letter" said Monday on CNBC.
"You can't say that a bear market has started until you've broken the trend lines—until you have rallied back, failed again, start to move lower. I'm not willing to say this is a bear market at all," said Dennis Gartman on "Fast Money." "I just think you're going to have a very severe, very substantive and really quite ugly correction that will probably make a lot of people wail and gnash their teeth before it's done."
(Read more: Market correction explained)
From disappointing economic data in the United States to unrest in emerging market currencies and Europe's sluggish economy, it's not any one event but a sudden combination of concerns that has spooked investors, he said.
As a result, Gartman thinks the S&P 500 index could fall 15 percent from the high reached last week, testing the 1,475 level on the downside.
(Read more: S&P has worst start to February since 1933)
He recommends going neutral on stocks, or as he put it, "stay on the sidelines."
—By CNBC's Drew Sandholm. Follow him on Twitter @DrewSandholm.