“We now hear almost every day that banks will not lend to each other, or will do so only at punitive interest rates. Credit spreads — the difference between what it costs the government to borrow and what private-sector borrowers must pay — are at historic highs.

This is not due to a lack of money available to lend, Ms. Schwartz says, but to a lack of faith in the ability of borrowers to repay their debts. “The Fed,” she argues, “has gone about as if the problem is a shortage of liquidity. That is not the basic problem. The basic problem for the markets is that [uncertainty] that the balance sheets of financial firms are credible.”

“In the 1930s, as Ms. Schwartz and Mr. Friedman argued in “A Monetary History,” the country and the Federal Reserve were faced with a liquidity crisis in the banking sector. As banks failed, depositors became alarmed that they’d lose their money if their bank, too, failed. So bank runs began, and these became self-reinforcing: “If the borrowers hadn’t withdrawn cash, they [the banks] would have been in good shape. But the Fed just sat by and did nothing, so bank after bank failed. And that only motivated depositors to withdraw funds from banks that were not in distress,” deepening the crisis and causing still more failures.

But “that’s not what’s going on in the market now,” Ms. Schwartz says. Today, the banks have a problem on the asset side of their ledgers — “all these exotic securities that the market does not know how to value.”

“Why are they ‘toxic’?” Ms. Schwartz asks. “They’re toxic because you cannot sell them, you don’t know what they’re worth, your balance sheet is not credible and the whole market freezes up. We don’t know whom to lend to because we don’t know who is sound. So if you could get rid of them, that would be an improvement.” The only way to “get rid of them” is to sell them, which is why Ms. Schwartz thought that Treasury Secretary Hank Paulson’s original proposal to buy these assets from the banks was “a step in the right direction.”

“The problem with that idea was, and is, how to price “toxic” assets that nobody wants. And lurking beneath that problem is another, stickier problem: If they are priced at current market levels, selling them would be a recipe for instant insolvency at many institutions. The fears that are locking up the credit markets would be realized, and a number of banks would probably fail.”

How did we get into this mess in the first place? As in the 1920s, the current “disturbance” started with a “mania.” But manias always have a cause. “If you investigate individually the manias that the market has so dubbed over the years, in every case, it was expansive monetary policy that generated the boom in an asset.

“The particular asset varied from one boom to another. But the basic underlying propagator was too-easy monetary policy and too-low interest rates that induced ordinary people to say, well, it’s so cheap to acquire whatever is the object of desire in an asset boom, and go ahead and acquire that object. And then of course if monetary policy tightens, the boom collapses.”

“The house-price boom began with the very low interest rates in the early years of this decade under former Fed Chairman Alan Greenspan.”

“In general, it’s easier for a central bank to be accommodative, to be loose, to be promoting conditions that make everybody feel that things are going well.”

WSJ – Weekend Interview