"You are not here to tell me what to do. You are here to tell me why I have done what I have already decided to do," Montagu Norman, the Bank of England’s longest-serving governor (1920-1944), is reputed to have once told his economic adviser. Today, thankfully, central banks aim to be more transparent in their decision making, as well as more rational. But achieving either of these things is not always easy. With the most laudable of intentions, the Federal Reserve, America’s central bank, may be about to take a step that could backfire.

Unlike the Fed, many other central banks have long declared explicit inflation targets and then set interest rates to try to meet these. Some economists have argued that the Fed should do the same. With Alan Greenspan, the Fed’s much-respected chairman, due to retire next year—after a mere 18 years in the job—some Fed officials want to adopt a target, presumably to maintain the central bank’s credibility in the scary new post-Greenspan era. The Fed discussed such a target at its February meeting, according to minutes published this week. This sounds encouraging. However, the Fed is considering the idea just when some other central banks are beginning to question whether strict inflation targeting really works.

At present central banks focus almost exclusively on consumer-price indices. On this measure Mr. Greenspan can boast that inflation remains under control. But some central bankers now argue that the prices of assets, such as houses and shares, should also somehow be taken into account. A broad price index for America which includes house prices is currently running at 5.5%, its fastest pace since 1982. Inflation has simply taken a different form.

Should central banks also try to curb increases in such asset prices Mr. Greenspan continues to insist that monetary policy should not be used to prick asset-price bubbles. Identifying bubbles is difficult, except in retrospect, he says, and interest rates are a blunt weapon: an increase big enough to halt rising prices could trigger a recession. It is better, he says, to wait for a housing or stock market bubble to burst and then to cushion the economy by cutting interest rates—as he did in 2001-2002.

And yet the risk is not just that asset prices can go swiftly into reverse. As with traditional inflation, surging asset prices also distort price signals and so can cause a misallocation of resources—encouraging too little saving, for example, or too much investment in housing. Surging house prices may therefore argue for higher interest rates than conventional inflation would demand. In other words, strict inflation targeting—the fad of the 1990s—is too crude.

We can learn from the third paragraph that（）

A. increases in asset prices are interfered by the Federal Reserves

B. more emphasis should be placed on consumer-price indices

C. changes have taken place in the pattern of inflation

D. inflation have been brought under federal control