在佩里·梅尔林（Perry Mehrling）关于货币与银行业的开篇讲座中，有一个令人印象深刻的时刻——这门课程他在纽约巴纳德学院（Barnard College）教授了多年。在讲座中，梅尔林回忆了自己对货币与金融问题产生浓厚兴趣的起源。多亏了互联网的便利，这段讲座录像如今任何人都可以观看。他的眼神中闪烁着光芒，那份热情显而易见。
THERE IS A moment in Perry Mehrling’s opening lecture on money and banking, a course he taught for years at Barnard College in New York, when the professor recalls the origins of his intellectual passion. (Thanks to the magic of the internet, the recording is available for anyone to watch.) His eyes light up. His enthusiasm is laid bare. He went to the library, he remembers, saw a shelf full of treatises on money, and said to himself, “If I could have a life reading all of those books, just from left to right, that would be the best life ever.”
他回忆道：自己曾去图书馆，看到书架上摆满了关于货币的学术著作，于是心想：“如果我能一辈子都用来阅读这些书，那该是多么美好的生活啊！”这种对知识的渴望使他与大多数主流经济学家截然不同。主流经济学家更喜欢阅读文章而非书籍；他们的学术体系几乎完全忽略了货币本身的本质。他们关注的是商品的生产与交换过程，而非那些在交易过程中被传递的纸币本身。有一句著名的对联很好地概括了他们的观点：“支付承诺既非食物，亦非衣物。”
His best life set him apart from most mainstream economists. They read articles, not books. And their intellectual framework leaves surprisingly little room for money. They care about the production and exchange of stuff, not the pieces of paper that change hands along the way. A famous couplet sums up their creed: “promises of payment/Are neither food nor raiment”.
然而，一旦你做出了支付承诺，你就需要货币来履行这个承诺——而非食物或衣物。这种“支付约束”（即履行承诺所需的资金）正是梅尔林自己学术思想的出发点。他承认自己的理论体系属于一个相对小众的学术流派，但他并不感到孤独。他的思想源泉包括许多杰出的经济学家，比如特立独行的美国经济学家海曼·明斯基（Hyman Minsky）以及《经济学人》（The Economist）杂志的第三任主编沃尔特·白芝浩（Walter Bagehot）；“他们都是非常了不起的人，”他在讲座中这样告诉听众。
But if you have made a promise of payment, you will need money, not food or raiment, to fulfil it. That “settlement constraint” is a starting point of Mr Mehrling’s own school of thought, which he called “the money view”. It is a little school, he admitted. But he did not feel alone.
梅尔林还激励了许多追随者，例如数据科学家丹尼尔·尼尔森（Daniel Neilson）以及国际清算银行（Bank for International Settlements）的伊纳基·阿尔达索罗（Iñaki Aldasoro）。伊纳基·阿尔达索罗专门为纪念梅尔林而撰写了一篇研究论文，该论文在梅尔林去世后不久（他年仅67岁）便发表了。
He drew on a shelfful of intellectual ancestors, such as Hyman Minsky, a maverick American economist, and Walter Bagehot, the third editor of this newspaper. (“They’re pretty great guys, actually,” he assures his lecture audience.) He also inspired other adherents, such as Daniel Neilson, a data scientist, and Iñaki Aldasoro of the Bank for International Settlements, whose own interpretation, dedicated to Mr Mehrling’s memory, was published this month, shortly after the professor’s untimely death at the age of 67.
按照这一传统，货币源于支付承诺。假设我欠你东西。也许这笔债务写在一张纸上。如果你信任我，你可能会接受这张纸，代替我立即偿还债务。你甚至可能试图把这张纸给别人，以清偿你自己的债务。如果他们也信任我——或者确信其他人都信任我——他们就可以从你手中接过我的这张纸，作为你对他们的债务的结算。我的欠条开始像货币一样流通。
According to this tradition, money evolves out of promises of payment. Suppose I owe you something. Perhaps that obligation is written on a piece of paper. If you trust me, you might accept that paper in lieu of immediate satisfaction of my debt. You might even try offering it to someone else to clear a debt of your own. If they too trust me—or feel confident that everyone else does—they could take my paper from you as settlement of your obligation to them. My IOU begins to circulate like money.
一个复杂的、层级分明的机制确保某些承诺被常规接受为货币。主流经济学家只关注这个系统的几个部分。他们痴迷于抑制通胀的政策规则，确保货币相对于商品和服务保持其价值。梅尔林先生对剩下的管道部分着迷。他问，什么确保银行账户、货币市场基金或离岸存款中的美元，与更高级的承诺（如央行准备金）保持平价？他将“平价”——不同种类美元之间的一对一汇率——视为货币的“四个价格”之一，其重要性不亚于熟悉的利率、汇率和商品与服务价格水平这三者。
A complex, hierarchical apparatus ensures that some promises are routinely accepted as money. Mainstream economists concentrate on only a few parts of this system. They obsess over the policy rules that curb inflation, ensuring that money holds its value against goods and services. Mr Mehrling was fascinated by the rest of the plumbing. What, he asked, ensures that the dollars in a bank account, a money-market fund or an offshore deposit hold their value, at par, with higher breeds of promise, such as reserves at the central bank? He treated “par”—the one-for-one exchange rate between different kinds of dollars—as one of “four prices” of money, as important as the familiar trio of the interest rate, exchange rate and the price level of goods and services.
平价通常鲜少引人关注。公众对其维持稳定充满信心，以至于几乎不知其存在。顺境中，银行乐于放贷并创造存款，增添新的支付承诺。这种“弹性”助经济繁荣。但也可能酿成张力。且不仅是体系规模在膨胀，其范围也在扩大。更广泛的参与者发行更为花样繁多的债权，指望它们能像货币般流通，且鲜少受到质疑。历史上，离岸银行创设的欧洲美元市场即为一例。货币市场基金是另一例。阿尔达索罗指出，这种模式的“最新迭代”是稳定币，即试图与既有货币维持平价的加密工具。
Par normally attracts little attention. The public is so confident it will hold, they barely know it exists. In good times banks happily extend loans and create deposits, adding new promises to pay. This “elasticity” helps the economy flourish. But it can create strains. And the scale of the system is not the only thing that grows. Its scope also expands. A wider range of actors issue a more exotic mix of claims in the hope they will circulate like money, with few questions asked. One historical example is the Eurodollar market created by offshore banks. Money-market funds are another. The “latest iteration” of this pattern, points out Mr Aldasoro, are stablecoins, crypto instruments that try to keep par with established currencies.
但一旦信心动摇，平价便受考验。发行低层级货币的机构往往无法独自通过此测试。它们不得不求助于层级更高的机构。2007-09年全球金融危机期间，发行美元债权的外国银行求助于各自的本国央行，后者又获得了美联储的援助。当稳定币面临类似考验时，迄今为止它们无处求援。但货币体系最终或许也会将其纳入管辖。
But when confidence is shaken, par is tested. Institutions that issue lower forms of money often cannot survive this test alone. They have to turn to institutions higher up the hierarchy for help. In the global financial crisis of 2007-09 foreign banks, issuing dollar claims, turned to their local central banks, which in turn received help from the Federal Reserve. When stablecoins have faced a similar test, they have so far had nowhere to turn. But the monetary apparatus may eventually domesticate them, too.
梅林教授遗憾地将无法亲历记录这一演变。其职业生涯中出版了四部著作。另一部阐述其货币观的专著尚未完成半部。或许它终将以某种形式面世。那货币学经典的书架上，仍有空位留待更多佳作。
Mr Mehrling will sadly not be around to document this evolution. During his career he published four books of his own. Another treatise setting out his money view remains half-written. Perhaps it will still see the light of day in some form. There is room on that shelf of monetary classics for more.