Why are interest rates so low? What are the chances that they will soon rise? These questions matter not just to central bankers and financiers but also to business people, savers and the wider population.

为何利率如此之低？它们很快上涨的几率有多大？这些问题不仅对央行官员和金融家们重要，而且对商人、储户以及一般人也很重要。

Let us start with the facts. The intervention rates of the four most important central banks of the high-income countries — the Federal Reserve, European Central Bank, Bank of Japan and the Bank of England — are all close to zero. These rates have been extremely low since soon after the worst of the global financial crisis, in September and October 2008.

让我们先来看一些事实。高收入国家最重要的四家央行——美联储(Fed)、欧洲央行(ECB)、日本央行(BoJ)和英国央行(BoE)——的干预利率全都接近于零。在2008年9月和10月全球金融危机全面爆发之后不久，这些利率就一直处于极低的水平。

In addition, all these central banks have expanded — or, in the cases of the ECB and the BoJ, are now expanding — their balance sheets, with a view to lowering interest rates on longer-term government bonds.

此外，为了降低较长期政府债券的利率，这些央行全都扩张了它们的资产负债表——或者就欧洲央行和日本央行而言，仍在扩张资产负债表。

Partly as a result, long-term interest rates on conventional bonds have also fallen to extremely low levels: in mid-September 2015, yields were 0.3 per cent on 10-year Japanese government bonds; 0.7 per cent on the German bonds; 1 per cent on French bonds; 1.8 per cent on Italian and UK bonds; and 2.1 per cent on US bonds.

这在一定程度上也造成常规债券的长期利率也降至极低水平：2015年9月中旬，日本十年期政府债券的收益率为0.3%；德国债券的收益率为0.7%，法国债券是1%，意大利和英国债券是1.8%，而美国债券是2.1%。

This is not just a story of low nominal rates. Global real interest rates on safe bonds have averaged only 2 per cent since 2000. Currently, they are not far from zero.

这不仅仅是名义利率偏低的故事。自2000年以来，全球安全债券的实际利率平均仅为2%。而现在它们已经离零利率不太远。

Ten-year US Treasury inflation-protected securities (TIPS) yielded 0.6 per cent in late September, while even 30-year TIPS yielded just 1.3 per cent. According to Andy Haldane, the Bank of England’s chief economist, these are the lowest real interest rates for 5,000 years. This is what John Maynard Keynes meant by the “euthanasia of the rentier”. Not surprisingly, rentiers hate it.

美国十年期通货膨胀保值债券(TIPS)在9月末的收益率为0.6%，即便是30年期TIPS的收益率也仅为1.3%。据英国央行首席经济学家安迪哈德恩(Andy Haldane)称，这些实际利率是5000年来最低的。这就是约翰蔠纳德凯恩斯(John Maynard Keynes)所说的“食利者的安乐死”。并不令人意外的是，食利者憎恨这种低利率。

There are three big-picture explanations of the combination of highly stimulative monetary policies, ultra-low nominal and real interest rates and the absence of inflation. The first is monetary; the second is real; and the third is real, monetary and financial. This last lies at the heart of my book, The Shifts and the Shocks.

至于为何出现这种高度刺激性的货币政策、名义和实际利率超低以及没有通胀迹象的组合，有三种宏观的解释。首先是货币因素，其次是实际因素，第三是实际因素加上货币和金融因素。最后一点是我在《转折与冲击》(The Shifts and the Shocks)一书中阐述的核心观点。

The first explanation is that of the Bank for International Settlements. As its Annual Report argues: “Rather than just reflecting the current weakness, low rates may in part have contributed to it by fuelling costly financial booms and busts. The result is too much debt, too little growth and excessively low interest rates. In short, low rates beget lower rates.”

第一种解释是国际清算银行(Bank for International Settlements)的解释。该行在其年度报告中辩称：“低利率并非仅仅反映出当前的疲弱，它可能通过助长代价高昂的金融繁荣和萧条，在一定程度上加剧了当前的疲弱。结果是过多的债务，增长乏力以及利率水平极低。简言之，低利率导致了更低的利率。”

The objection to this view is that it rests on the assumption that monetary policy is able to distort long-term interest rates — among the most important of all prices — for decades. It rests, too, on the assumption that pursuing such ultra-easy policies will show up not at all in inflationary pressure, but exclusively in the behaviour of the financial system. This seems wildly implausible.

这种观点站不住脚的一个理由是，它基于这样一个假设：货币政策能够持续几十年一直扭曲长期利率——长期利率处于最重要的价格之列。它还假设：实施此类超级宽松政策将完全不会体现在通胀压力上，而只是体现在金融体系的行为上。这似乎完全说不通。

At the heart of the second explanation lie shifts in the desire to save and invest. This is the“savings glut” hypothesis of Ben Bernanke, former chairman of the Federal Reserve. Mr Haldane elaborates this hypothesis as “excess savings in the east, deficient investment in the west, worsening demographic trends and rising inequality”.

第二种解释的核心在于储蓄和投资意愿的转变。这是美联储前主席本伯南克(Ben Bernanke)的“储蓄过剩”假说。哈德恩将这种假说概括为“东方储蓄过剩，西方投资不足，人口结构趋势日益恶化，不平等程度不断加剧”。

The difficulty with this analysis is that it gives no explanation for the financial crisis. If one holds to this explanation, one has to argue that the crisis was just the result of foolish deregulation and wild profit-seeking in an irresponsible financial sector. That, too, seems implausible. The question has to be: why did such a huge crisis happen just when it did?

这种分析的问题在于，它没有对此次金融危机做出解释。如果有人坚持这种解释，他不得不辩称，危机只是愚蠢的放松监管以及不负责任的金融行业疯狂逐利的结果。这似乎也不太可信。人们不得不质问：为什么如此巨大的危机偏偏在那个节骨眼上爆发？

The third (and, in my view, correct) explanation is a synthesis of the other two. The simplest form of that synthesis is the Keynesian view: the short-run equilibrium in the economy is determined by the intersection of real and monetary forces. The former determine equilibrium (or natural) interest rates, which the central bank then seeks to deliver.

第三种解释是其他两种解释综合而成（在我看来，这种解释是正确的）。最简单的综合是凯恩斯的观点：经济中的短期均衡由实际因素和货币因素共同决定。实际因素决定了均衡（或称自然）利率，央行随即寻求提供这样的利率。

Yet, in seeking to deliver the monetary conditions needed for equilibrium between savings and investment at high levels of activity, the central bank has to encourage credit growth. But that credit growth might be — and in recent decades has been — highly destabilising, because it requires massive leveraging, particularly of property assets, and leads to financial booms and busts.

然而，为了在高经济活动水平下提供储蓄和投资均衡所需的货币条件，央行不得不鼓励信贷增长。但那种信贷增长可能极大地破坏稳定（在最近几十年就是如此），因为它需要庞大的杠杆（尤其是对房地产资产），导致金融盛衰。

The correct story, then, is of the interaction between real forces on the one hand, and monetary and financial forces on the other. The savings glut was a causal factor. But its impact came via monetary policy and the financial system, and so via financial booms and busts.

因此，正确的解释是实际因素与货币和金融因素共同作用的结果。储蓄过剩是一个诱因，但其影响是通过货币政策和金融体系传递的，进而通过金融盛衰产生冲击。

So what does this view imply for the future of world interest rates? Here are five implications.

那么，这种观点对未来的世界利率意味着什么？这里有5个方面的涵义。

First, people feel that savings have to be valuable. On average, they are. But at the margin, they are not. And the price of anything is decided at the margin. In this case, it is zero.

首先，人们觉得，储蓄必须有价值。一般来说确实如此。但在边际领域，它们没有价值。所有物品的价格都由边际领域决定。在这种情况下，它是零。

Second, the bursting of the credit bubble in the high-income economies led to another huge credit bubble, this time in China.

其次，高收入经济体的信贷泡沫破裂导致又一个巨大的信贷泡沫，这次是在中国。

Third, after the end of the Chinese bubble, the global savings glut is likely to grow in coming years. China has a national savings rate not far short of 50 per cent of gross domestic product. But its investment rate (which is almost as high) seems sure to fall.

第三，在中国泡沫结束之后，全球储蓄过剩现象可能在今后几年加剧。中国国民储蓄与国内生产总值(GDP)之比接近50%，但其几乎同样高的投资比率似乎必然会下降。

Fourth, the debt overhangs created by the western and subsequent Chinese credit booms have been large enough to constrain spending for a long time.

第四，西方以及随后的中国信贷繁荣遗留了巨额债务，足以在很长时期内遏制支出。

Finally, for strong global growth, we would seem to need another credit boom somewhere. But where might that happen? The obvious candidate for another such boom would be the US. If so, weak global demand is likely to keep US interest rates very low.

最后，要想实现全球经济的更强劲增长，我们似乎需要其他地方再来一场信贷繁荣。但是可能在哪里呢？一个明显的候选地将是美国。若果真如此，疲弱的全球需求可能让美国利率保持在极低水平。