David Einhorn, founder and president of Greenlight Capital, returned to New York's annual Sohn Investment Conference Wednesday, unveiling his firm's bearish case on Caterpillar (CAT) - Get Report and more bullish outlook on General Motors (GM) - Get Report .

Einhorn argued that a rebound in Caterpillar shares will depend on the two big drivers of its mining business -- coal and iron ore --both of which are unlikely to rebound in the short or medium terms, he said.

"Betting on a big recovery is betting on a big recovery in resources," he said. "We don't see a return in capital investment in coal mining, maybe ever," he added, noting that iron ore prices also seem to have a long way to go before hitting bottom.

Einhorn estimated that Caterpillar, whose shares are down 15% over the past 12 months, will likely bottom in 2018, as "somewhere around half its share price," Einhorn said.

Meanwhile, he unveiled Greenlight's more bullish stance on GM, highlighting the car maker's favorable geographical demand prospects as well as over-excitement surrounding electric cars and ride-sharing apps such as Uber.

He also pointed to a healthy free cash flow that GM management will most likely use to buy back shares, increasing the earnings-per-share value on the remaining stock in circulation.

See full coverage from the Sohn Investment Conference here. The event brings together some of the top minds in the financial world for a day of sharing investment ideas. It is held in honor of Ira Sohn, a Wall Street professional who lost his battle with cancer when he was 29. Proceeds from the New York conference, as well as other conferences the Sohn Conference Foundation holds, are dedicated to the treatment and cure of pediatric cancer and other childhood diseases. The foundation has so far raised more than $65 million.