Even scholars who support the inquiry say they aren’t sure that researchers will be able to prove the connection. Richard B. Freeman, an economist at Harvard, is comparing about 125 financial crises around the globe that occurred over the last 30 years. He said inequality soared before many of these crises. But, Mr. Freeman added, the data from different nations is difficult to compare. And Professor Freeman says he has found some places, like the Scandinavian countries, where there were crises without much inequality, suggesting that other factors, like deregulation, may be the best explanations.

For his part, Mr. Moss said that income inequality might have complicated links to financial crises. For instance, inequality, by putting too much power in the hands of Wall Street titans, enables them to promote policies that benefit them — like deregulation — that could put the system in jeopardy.

Inequality may also push people at the bottom of the ladder toward choices that put the financial system at risk, he said. And low-income homeowners could have better afforded their mortgages if not for the earnings gap.

(Mr. Hubbard has a different take: He says many lower-income homeowners should not have had mortgages in the first place. The latest crisis, he says, was caused by policymakers who decided to “democratize credit” by expanding home ownership. Their actions were driven by a desire to address inequality, but those policymakers were misguided and should have improved education instead, he adds.)

Scholars who study inequality often focus on people at the bottom. But, Mr. Moss said, the incentives of people at the top also deserve more scrutiny.

He pointed to the recent work of Margaret M. Blair, who teaches at Vanderbilt University Law School and is active with the Tobin Project, the nonprofit organization Mr. Moss founded a few years ago to study issues like economic inequality. She is researching whether financial workers promote bubbles and highly leveraged systems, even unconsciously. Ms. Blair said that because financial bubbles often lead to higher returns, financial workers have the potential to make more, and this pattern can influence their trading strategies and the policies they promote. Those decisions, in turn, drive even greater income inequality, she said.