Siegel: Keep buying—you 'can’t lose'

Wharton professor Jeremy Siegel has long been bullish on the market—and over the past few years, he's been dead-on.

In early 2012, he famously called for Dow 15,000 by the end of 2013, and after enduring much mockery, Siegel saw the index hit his target in May.

The bull isn't changing his stripes. As the market has risen, Siegel's targets have, too.

On the Dow, "my target is 16,000 to 17,000 for the end of this year," Siegel said on Tuesday's "Futures Now." "And I think 18,000 is definitely achievable in 2014."

Why is Siegel so unabashedly bullish? Because he believes the market is in the midst of a uniquely bullish tug of war.

On one side is the Federal Reserve's quantitative easing program, which is pushing down bond yields. On the other is an economy that Siegel believes will accelerate in the second half of the year.

"The market is totally spooked by whether QE continues or not," Siegel said, but the Fed "would never accelerate tapering unless the economy was so much stronger, which has got to be good for earnings. So in one way, you can't lose on stocks—either the economy's weak, the tapering will end; or the economy's strong, they'll taper, and earnings will be strong. That's why I think stocks are still a win-win situation."

And this is all against the backdrop of a market that has not yet become expensive, even by historical measures.

"Equities' valuation right now is just about at its historical average, but one has to realize that that's the average of when interest rates were as high as 15 and 20 percent, and as low as they are today," Siegel said. "When you're in a low or moderate interest rate environment, price-to-earnings ratios of 18 and 19 are actually more typical—and we're not there yet."

Siegel added: "So I think this bull has some space to run."

—By CNBC's Alex Rosenberg. Follow him on Twitter: @CNBCAlex.

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