It’s not clear that the market today presents a “buying opportunity,” he said, pointing to continuing structural problems in the economy. “There is no golden rule that says how much a market should go down,” he said.

Even after the market eventually rebounds, he said, people who expect annual returns of 9 or 10 percent will be disappointed. “Over the next five years,” he said, “annual returns of 4 to 5 percent are in the range that people might expect.”

Dr. Kaufman said that several popular investing theories “have fallen apart.” With nearly all asset classes moving in tandem, he said, diversification hasn’t been of much help, and global investing hasn’t worked out very well, either.

“Many markets outside the United States are down more than the American markets,” he said, “and certainly, in terms of flight to safety, in the fixed-income side, the money is coming back here rather than going out there.”

And, he said, Wall Street’s faith in “quantitative risk analysis” has been battered. “It didn’t save anything or anybody,” he said.

What should investors do under these circumstances? Buy high-quality corporate bonds, which fell sharply over the last year or so, and which are likely to rise in a market recovery. That makes sense to Dr. Kaufman, as well as Messrs. Wien, Biggs and Lynch. Bonds have the merit of providing steady income, at rates that are now very high; they tend to be less volatile than stocks; and they have a higher legal claim on a company’s assets.

FOR investors with a truly long-term view, probably 20 years or more, the market will be worthwhile, they said, because stocks should outperform other asset classes. To one degree or another, though, they said investors should be extremely cautious over the short term.