“In an environment of extraordinary uncertainty, the traditional role of asset allocation and long-term investing is far more difficult,” said Michael Sonnenfeldt, chief executive of Tiger 21, a forum for wealthy investors who meet monthly to discuss financial matters. “Many of our members believe we are in a trader’s market where long-term investing should be shunned but trading opportunities should be seized.”

Indeed, many investors are reluctant to place longer term bets and cling to larger cash allocations, anticipating continued volatility.

“The landscape going forward is extremely uncertain,” said Hans Olsen, chief investment officer at J.P. Morgan’s private wealth management unit. “There are many possible outcomes. You need to have a portfolio structured to reflect many possible futures. It comes down to the first principles of diversification.”

But how you define diversification is evolving.

“In a bull market, we don’t tend to care that our portfolio investments seem to behave the same, but I believe this bear market has uncovered a long-term problem,” said Jerry Verseput, a financial planner in El Dorado Hills, Calif., noting that technology and globalization have diluted the effectiveness of diversification based on company size and location. So he has embraced a new approach, using a portfolio of exchange-traded funds, or E.T.F.’s, that track different sectors of the economy, like energy and health care.

Below, several investment professionals describe how their philosophies have changed and how they are reallocating their portfolios. And one stalwart traditionalist explains why he thinks all of this is a lousy idea.