Ms. Admati said she started asking one question repeatedly: Why were banks behaving so differently? Companies with more debt are more vulnerable to financial setbacks. Banks were in the danger zone, so why not raise more equity?

Four years later, she says she’s still waiting to hear a good answer. She recalled the explanation in one prominent banking textbook, which she read in 2010, as a particular spur to action. “It was shocking,” she remembered. She said she went to the office of a Stanford colleague, her frequent collaborator Paul Pfleiderer, and told him: “Something is very wrong. I’ve never heard so much nonsense in all of my life.” She still becomes visibly angry as she recalls the conversation. “They are denying what we know about financial markets. It’s like they are saying gravity is not a force in nature.”

Ms. Admati decided to enter the public square because she felt that academics and policy makers weren’t listening. “The Bankers’ New Clothes,” which she wrote with Martin Hellwig, an economics professor at the University of Bonn, proved a turning point in her campaign. But the first step was much smaller. She was not sure how to reach a popular audience, so in 2010 she enrolled in a program that teaches prominent women to write opinion articles. Her first, published in The Financial Times in the fall of 2010, was a letter co-signed by 19 other academics that criticized an international agreement on minimum bank capital standards as “far from sufficient to protect the system from recurring crises.”

Banking is the only industry subject to systematic capital regulation. Borrowing by most companies is effectively regulated by the caution of lenders. But the largest lenders to banks are depositors, who generally have no reason to be cautious because federal deposit insurance guarantees repayment of up to $250,000 even if the bank fails. This means the government, which takes the risk, must also impose the discipline.

In the decades before the financial crisis, banks gradually convinced regulators to reduce capital requirements to very low levels. In the aftermath, banks acknowledged that some increases were necessary — they had just needed enormous bailouts, after all — but they fought to minimize those increases. The day after Ms. Admati’s article ran, the same paper ran one by Vikram S. Pandit, then the chief executive of Citigroup, arguing that the proposed standards were excessive. “The last thing the global economy needs is another economic dampener,” Mr. Pandit wrote.

Image Ms. Admati, right, with two other finance professors — Deniz Anginer of Virginia Tech. left, and Edward Kane of Boston College — at a Senate committee hearing. Credit... Mary F. Calvert for The New York Times

‘Add a Digit’

The industry has benefited from, and sometimes encouraged, public confusion. Banks are often described as “holding” capital, and capital is often described as a cushion or a rainy-day fund. “Every dollar of capital is one less dollar working in the economy,” the Financial Services Roundtable, a trade association representing big banks and financial firms, said in 2011. But capital, like debt, is just a kind of funding. It does the same work as borrowed money. The special value of capital is that companies are under no obligation to repay their shareholders, whereas a company that cannot repay its creditors is out of business.