OSLO, Norway -- Henrik Syse, a professional philosopher, says he gets ribbed by his family that "five of my 10 best friends are dead Greeks." But this fall he put aside writing a book on Plato to ponder a more practical puzzle: what to do with around $190 billion?

Mr. Syse started work in September as the in-house ethicist for the Norwegian government's Petroleum Fund, one of the world's largest pools of investment capital. "It has been a steep learning curve," says the 39-year-old academic. "I'm a philosopher. I'm not a banker."

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