The first factor dealt with valuation.
"I'm a little concerned that we got a little buoyant on the upside," he said.
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Gartman also said that last week's strong employment numbers could give traders the notion that the Fed might tighten its monetary easing policy sooner than expected.
Despite his call to neutrality, Gartman said that he still has an overall bullish outlook on the markets, and he's remaining long in a number of core positions, including Apple and Alcoa.
"I've written calls against them, I have some derivates to bring that net position back to almost net neutrality," he said.
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As for those with a longer-term approach, Gartman said things are generally looking up for the markets and the economy.
"I think we're going to have a great five years. I think we're going to be surprised at how strong the U.S. economy is going to be, and even how strong the global economy is going to be," he said.
—By CNBC's Michael Newberg