In short, the recent crisis has underscored the need both to strengthen our monetary policy and financial stability frameworks and to better integrate the two. We have made progress on both counts, but more needs to be done. In particular, the complementarities among regulatory and supervisory policies (including macroprudential policy), lender-of-last-resort policy, and standard monetary policy are increasingly evident. Both research and experience are needed to help the Fed and other central banks develop comprehensive frameworks that incorporate all of these elements. The broader conclusion is what might be described as the overriding lesson of the Federal Reserve's history: that central banking doctrine and practice are never static.

I still believe the following, which is that monetary policy is a very blunt instrument. If you are raising interest rates to pop an asset bubble, even if you were sure you can do that, you might, at the same time, be throwing the economy into recession, which kind of defeats the purpose of monetary policy.

And therefore, I think the first line of defense—I mean, I think, we have a sort of a tripartite line of defense. We start off with very extensive and sophisticated monitoring at a much higher level and much more comprehensively than we’ve had in the past. Then we have supervision and regulation, where we work with other agencies to try to cover all the empty or uncovered areas in the financial system. And then, in addition, we try to use communication and similar tools to affect the way that financial markets respond to monetary policy. So we do have some first lines of defense, which I think should be used first.

That being said, you know, I think that given the problems that we’ve had—not just in the United States, but globally in the last 15, 20 years—that we need to at least take into account these issues as we make monetary policy. And I think most of the people on the FOMC would agree with that. What that means exactly depends on the circumstances. I think if the economy is in very weak condition and interest rates are very low for that purpose, it’s very difficult to contemplate raising rates a lot because you’re concerned about some sector in the financial sphere. On the other hand, if you’re in an expansion and there’s a credit boom going on, that—the case in that situation for making policy a little bit tighter might be better.

So, as I’ve said many times, I have an open mind in this question. We’re learning; all central bankers are learning. But I think I still would agree with the point I made in my very first speech in 2002, as a Governor at the Federal Reserve, where I argued that the first line of defense ought to be the more targeted tools that we have, including regulatory tools and, to some extent, macroprudential tools like some emerging markets use.

"Bubble, Bubble, Toil and Trouble: A Dangerous Brew for Monetary Policy"

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Sound policymaking requires us to understand the limits of what we know. I doubt we could find enough agreement among policymakers or economists about the interpretation of asset-price movements to allow for stable, rule-based policymaking. In the absence of such a clearly stated rule, we risk uncertainty about central bank policy itself as well as its effect on the economy... Humility in policymaking requires that we respect the limits of our knowledge and not overreach, particularly when it involves over-riding market signals with policy actions.

Another challenge in addressing asset-price bubbles in practice is that contrary to many economic models, in reality there are many assets, not just one. And these assets have different characteristics. For example, equities are very different from homes. Misalignments or bubble-like behavior may appear in one asset class and not in others. But monetary policy is a blunt instrument. How would monetary policy go about pricking a bubble in technology stocks in 1998 and 1999 without wreaking havoc on investments underlying other asset classes?

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Indeed, I believe that we are discussing the question of asset prices and monetary policy today, at least in part, because Fed policy during mid-2000s “went off track.” John Taylor has argued forcefully that the Fed kept interest rates too low for too long from 2003 to 2005. As an erstwhile member of the Shadow Open Market Committee, I stood in this very room in 2003 and 2004, expressing concerns that the fears of deflation were excessive and that policy was probably too accommodative. The error may not have been that policymakers failed to pay attention to the fast upward rise in asset prices, but that they deviated from a systematic approach to setting nominal interests.

I think we’re in a liquidity trap where there is excess savings, greater than investment. It would take a lower real interest rates to address that.

But, look, if the right thing to do for the macro economy is to have lower interest rates but that comes with some risk for the financial system, we’ve only got one monetary policy tool and we have to focus on our mandate. But we have other supervisory tools which are supposed to  address emerging risks in financial markets. I think they have to be used.

I will try to define some of the important characteristics of asset price bubbles. I will argue that bubbles do exist and that bubbles typically occur after an innovation that has created uncertainty about fundamental valuations. This has two important implications. First, a bubble is difficult to discern and, second, each bubble has unique characteristics. This implies that a rules-based approach to bubbles is likely to be ineffective and that tackling bubbles to diminish their potential to destabilize the financial system requires judgment.

I will try to define some of the important characteristics of asset price bubbles. I will argue that bubbles do exist and that bubbles typically occur after an innovation that has created uncertainty about fundamental valuations. This has two important implications. First, a bubble is difficult to discern and, second, each bubble has unique characteristics. This implies that a rules-based approach to bubbles is likely to be ineffective and that tackling bubbles to diminish their potential to destabilize the financial system requires judgment.

That said, there is some evidence that a tighter monetary policy will reduce desired leverage in the financial system by flattening the yield curve and reducing the profitability of maturity transformation activities.¹² To the extent this is true, that may imply a somewhat more favorable trade-off in “leaning against” a bubble. More research is needed on this subject. For now at least, monetary policy appears to be inferior to macroprudential tools that seek either to limit the size of prospective bubbles or to strengthen the financial system so that it is more resilient when asset prices fall sharply.

One type of cost arises because monetary policy is a blunt instrument...

We simply do not have good theories or empirical evidence to guide policymakers in using short-term interest rates to limit financial speculation. Given our current state of knowledge, my preference at this time would be to use regulation and supervision to strengthen the financial system and lean against developing problems. Monetary policy would be used only if imbalances were building and regulatory policies either were unavailable or had proven ineffective. The homework assignment is to improve our ability to identify incipient financial imbalances and understand their interactions with changes in policy interest rates.

While recent events have indeed imposed significant costs on society, I fear that monetary policy tools may be too blunt for such a fine-tuning policy.⁵ Central bankers have imperfect information, and for many asset classes, sudden price declines may have minimal impact on the real economy.⁶ So, my concern is that using monetary policy to "lean against bubbles" could end up causing more harm to the economy than good.

See Dudley's comments on asset price targeting.

In normal times, we use our policy instrument, the short-term federal funds rate, to try to achieve our dual mandate goals of maximum sustainable employment and price stability. Adding a third target—asset prices—would likely mean we couldn't do as well on the other two.

[I]f a dangerous asset price bubble is detected and action to rein it in is warranted, is conventional monetary policy the best tool to use? Going forward, I am hopeful that capital standards and other tools of macroprudential supervision will be deployed to modulate destructive boom-bust cycles, thereby easing the burden on monetary policy.5 However, I now think that, in certain circumstances, the answer as to whether monetary policy should play a role may be a qualified yes. In the current episode, higher short-term interest rates probably would have restrained the demand for housing by raising mortgage interest rates, and this might have slowed the pace of house price increases. In addition, tighter monetary policy may be associated with reduced leverage and slower credit growth, especially in securitized markets.6 Thus, monetary policy that leans against bubble expansion may also enhance financial stability by slowing credit booms and lowering overall leverage.

I would not advocate making it a regular practice to use monetary policy to lean against asset price bubbles. However recent experience has made me more open to action. I can now imagine circumstances that would justify leaning against a bubble with tighter monetary policy. Clearly further research may help clarify these issues.

More time and study will be needed before we can be confident about the lessons of the current crisis.  But... based on what we know today, I still have serious questions about whether trying to use monetary policy to check speculative activity on a regular, systematic basis would yield benefits that outweigh its costs.

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...in the 2006 speech I concluded that a strategy of extra action might be justified if three tough conditions were met.  First, policymakers must be able to identify bubbles in a timely fashion with reasonable confidence.  Second, a somewhat tighter monetary policy must have a high probability that it will help to check at least some of the speculative activity.  And third, the expected improvement in future economic performance that would result from the curtailment of the bubble must be sufficiently great.  Of course, we live in an uncertain world, and accordingly policymakers should always be open to the possibility that these conditions might be satisfied and that extra action would be appropriate.  But my thought at the time was that, in practice, the likelihood of ever meeting the three conditions seemed remote. 

Nonetheless, even if policymakers are confident that a bubble has emerged, the question of the timeliness of the call remains.  The essential problem is the timing of the detection of the bubble relative to the timing of its collapse.  The risk is that the detection and subsequent policy response occurs not long before the bubble collapses on its own.  Given the lags associated with monetary policy, the resulting contractionary effects on the economy of the monetary tightening would occur just when the adverse effects of the bubble's collapse are being realized, worsening rather than mitigating the effects of the bubble's collapse.  And the inevitable lags in detecting bubbles increases the likelihood that, by the time action is taken, speculative activity will have progressed to the point that its collapse is not far off. 

The likelihood of deflation, "whatever I thought that risk was four or five months ago, I think it's bigger now, even if it's still small," he said.   But, "A lesson I take from the Japanese experience is not to let that get ahead of us, to be aggressive in moving against that risk if we see it coming," Kohn said, responding to questions following a speech to the Cato Institute's 26th Annual Monetary Policy Conference 

While "some people have argued that we should save our ammunition, that interest rate cuts aren't effective, etcetera, I think that were we to see this possibility that we should be very aggressive with our monetary policy, as aggressive as we can be," Kohn said.   

From the audience Q&A, as reported by Market News

While policymakers have acknowledged that asset price excesses and their subsequent correction can potentially have meaningful consequences for the economy, they generally have preferred to try to cushion the repercussions of an asset price collapse rather than to address an asset price run-up in its early stages. There are, to be sure, good reasons for this attitude, having to do with the difficulty of identifying asset 'bubbles' in a timely way, the need to build public support for action, and the challenge of weighing the costs and benefits of action for the broad economy. Nevertheless, in view of the damage resulting from the decline in housing values, as well as the aftermath of the collapse of prices of technology stocks earlier this decade, I think it essential to revisit these issues.

Identification of excesses in asset prices, although challenging, does not appear to be beyond the realm of possibility. There is some work in academic circles, and at least some practitioners agree, that when common ratios (the ratio of stock prices to earnings or dividends, for example, or the ratio of housing values to rents) exceed the bounds of historical experience, it is likely that a price correction will follow, although its timing is unpredictable. It would seem likely that misidentification will occur occasionally and, in particular, that some events may be classified as bubbles when they are not.  The implication of this possibility is, in my view, to ensure that the policy response to a perceived excess in asset prices is measured, so that even if in error the ramifications for the economy will be modest.

This consideration illustrates, perhaps, the critical issue in addressing asset price excesses. When all is said and done, will the benefits outweigh the costs, assuming policymakers have made the correct identification? Monetary policy, for which we in the Federal Reserve are responsible, is a blunt instrument with economy-wide effects. We should not pretend that actions taken to rein in those asset price increases which seemingly outstrip economic fundamentals won't in the short run curtail to some extent economic growth and employment; after all, such actions are likely to require raising interest rates earlier and probably more than otherwise would be the case.