“Some have suggested that size alone, or the combination of investment banking and commercial banking, contributed to the crisis,” Jamie Dimon, JPMorgan Chase’s chief executive, said to the commission members. “We disagree.”

Mr. Dimon, of course, represents the interests of JPMorgan, which just happens to be one of the largest and most successful banks in the nation. And JPMorgan has been one of the biggest beneficiaries of the financial crisis, having picked up Bear Stearns and Washington Mutual along the way.

But there is a loud chorus of people taking issue with his stance and arguing that the sheer size of the banks — and worries about the effect of any of them failing — helped bring about the financial crisis.

Such concerns have led many people to question the repeal in 1999 of the Glass-Steagall Act, the Depression-era law that was enacted to prevent investment and commercial banks from combining. Alan Greenspan, former chairman of the Federal Reserve, has argued that a simple test should settle any debate. “If they’re too big to fail, they’re too big,” he said in October.

“In 1911 we broke up Standard Oil — so what happened? The individual parts became more valuable than the whole,” Mr. Greenspan added. “Maybe that’s what we need to do.”

It was a surprising statement from Mr. Greenspan, given his free-market comment in 2005 that “private regulation generally has proved far better at constraining excessive risk-taking than has government regulation.”

In other countries, like Britain, political leaders have openly called for the forced breakup of such institutions on the theory that more modest measures would not guard against future calamities.

“The belief that appropriate regulation can ensure that speculative activities do not result in failures is a delusion,” Mervyn A. King, governor of the Bank of England, said last year.

But shrinking the size of these companies may create other problems for the economy, particularly in this age of huge corporations.

If Pfizer, for example, needs to raise $20 billion for a takeover bid, or Verizon needs to raise billions to lay fiber optic cable for its FiOS service, they cannot efficiently go to 20 different community banks looking for the money. }

And if corporations can’t readily obtain financing in the United States, they may simply seek out huge overseas lenders like HSBC and Deutsche Bank.

“America’s largest companies operate around the world and employ millions of people,” Mr. Dimon said at the hearing. “These firms need banking partners that operate globally, offer a full range of products and services, and provide financing in the billions of dollars.”

Mr. Dimon also argued that there was no clear correlation between size and problems.

“If you consider the institutions that have failed during the crisis, many have been small,” he said. “Some of the largest and most consequential failures were firms that were principally engaged in one business.”

Think of the biggest dominoes: Bear Stearns, Lehman Brothers, Merrill Lynch andMorgan Stanley. They weren’t financial supermarkets.

Mr. Dimon was trying to make this point: Companies should be allowed to be as big as they want, so long as there is an orderly way to wind them down.

“The solution is not to cap the size of financial firms,” he said. “We need a regulatory system that provides for even the biggest bank to be allowed to fail, but in a way that does not put taxpayers or the broader economy at risk.”

That sounds good in theory. But in practice, the larger financial institutions become, the harder it is to keep them from impacting others — or taxpayers.

One piece of legislation making its way through Washington involves “resolution authority,” which would give the government the ability to put a too-big-to-fail financial company into a conservatorship in much the same way the Federal Deposit Insurance Corporation is able to unwind a commercial bank without putting it into bankruptcy.

In previous columns, I have argued in favor of resolution authority as a last-gasp measure to protect the financial system.

Mr. Dimon has also argued in favor of resolution authority as a way of allowing huge financial institutions to continue to operate with a safety net under them.

“Under such a system, a failed bank’s shareholders should lose their value; unsecured creditors should be at risk and, if necessary, wiped out,” he said. “A regulator should be able to terminate management and boards and liquidate assets.”

There is one problem, however, that often gets overlooked with resolution authority: the cost. It is not free for the government to take over a company the way it did Fannie Maeand Freddie Mac.

One solution would be to create a fund similar to deposit insurance, in which systemically important financial institutions would be assessed fees to cover the costs associated with failures in their ranks.

But consider this: the amount of money necessary to protect against the failure of a company like American International Group, for example, could be hundreds of billions of dollars. Financing that would require fees that could put a severe strain on companies and their profits.

What we really need is a resolution authority to resolve this debate.