经济学 1960

社会成本问题

罗纳德·科斯

当讨价还价无成本，法律只决定谁付钱——而非生产什么。

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In depth · the introduction

该让污染者付钱，还是受害者？科斯的答案出人意料：当双方可以自由讨价还价时，这并不会改变究竟生产出什么——改变的只是谁来开支票。

核心想法

我们通常把污染或妨害看作「一方伤害另一方」，于是去问该如何约束那个肇事者。科斯说，这个框架本身就错了。损害是双向的：踩坏农夫庄稼的牛群，与想要那些庄稼的农夫，不过是两个人为不同的用途，想要同一块地。拦住牛群，伤害的是牧场主；放牛去吃，伤害的是农夫。明智的问题是：哪一种用法更值钱。

接着是那个惊人之处。设想两人能交谈、能无成本地达成交易。科斯证明：无论法律是否要牧场主为损害买单，他们最终都会养下恰好正确的牛数——那个让肉与庄稼的总价值最大的数目。若牧场主不必担责，农夫会付钱请他少养几头；若牧场主须担责，他会自己少养几头。无论哪种，牛群一样多。法律决定的是谁最终更富，而不是究竟做了什么。

它是如何诞生的

罗纳德·科斯是一位英国经济学家，长于注意到别的经济学家假定掉的东西。在 1959 年一篇论无线电频谱的文章里，他主张应把电波当作财产来拍卖——并顺带抛出一句：在自由讨价还价下，谁先拿到电波其实无关紧要。芝加哥的经济学家们以为他犯了错。

于是他们请他到阿伦·迪雷克托家中赴宴，想纠正他。传说那一屋子人——米尔顿·弗里德曼、乔治·斯蒂格勒等——入席时坚信科斯错了，散席时却被说服他是对的。他们催他把它写出来；成果便是这篇 1960 年的论文。它把他带到了芝加哥大学，并在三十年后，把他带向了诺贝尔奖。

它为何重要

科斯悄然拆掉了那个条件反射：似乎每一桩损害都需要政府课税或下禁令。在人们能讨价还价之处，他们往往能自己摆平，而法律的职责，不过是把可供交易的权利界定清楚。但是——这才是他真正、却常被遗忘的要点——讨价还价通常并非无成本。当达成交易很难时，法律把权利判给谁，便确实决定了会发生什么。这一洞见，催生了一整个把法律与制度当作经济机器来研究的领域。

一个可以想象的画面

想象两个室友，一个爱打鼓，一个需要安静念书。共享的空气这份「权利」，无论归打鼓的还是归念书的，只要他们能商量，就会落在同一个安排上——比如，晚上八点前可以打鼓——因为那是对他们俩合起来最值钱的安排；他们只需互让个人情、或贴点房租，把它定下来。规则决定的是谁欠谁一份人情，而不是这一晚究竟怎么过。科斯真正要问的是：当「商量」本身代价太高时，会怎样——那时，规则便决定了一切。

它的位置

在科斯之前，教科书对外部性的解法是阿瑟·庇古的：对损害课税。科斯证明，这税既非理所当然、也并非总是对的。在他之后，法律经济学这一领域兴起，还有「总量管制与交易」这个务实的点子——创造出可交易的排污权，让市场把它挪到最能发挥作用之处。它与本馆中其他关于公地的难题并立：加勒特·哈丁的「公地悲剧」点出了问题，而埃莉诺·奥斯特罗姆则展示了：社群往往无需市场、也无需国家，就能治理好共享的资源。它们共同勾勒出：亚当·斯密那只看不见的手会在何处失灵——以及我们能为此做些什么。

The original document

Original source text

R. H. Coase · The Problem of Social Cost · Journal of Law and Economics, vol. 3 (October 1960), pp. 1–44

The reciprocal nature of the problem

We are dealing with a problem of a reciprocal nature. To avoid the harm to B would inflict harm on A. The real question that has to be decided is: should A be allowed to harm B or should B be allowed to harm A?

Coase writes against the standard view — Pigou's — that a business whose activity harms others should simply be taxed or restrained. The harm, he insists, runs both ways: stopping A from harming B imposes a cost on A. The real economic question is which use of the resources is the more valuable.

The cattle and the crops

To make the argument concrete Coase imagines a cattle-raiser whose herd strays onto a neighbouring farmer's land. Each extra steer tramples more crop than the last; in his table one steer destroys 1 ton of crop, two steers 3 tons, three steers 6 tons, and four steers 10 tons.

He then shows that whether or not the rancher is legally liable for the damage, a rancher and a farmer who can bargain freely will settle on the very same herd size — the one that maximises the combined value of meat and crops. The liability rule changes only who compensates whom, not how much is produced.

[ … ]

When the pricing system works without cost

It is necessary to know whether the damaging business is liable or not for damage caused since without the establishment of this initial delimitation of rights there can be no market transactions to transfer and recombine them.

the ultimate result (which maximises the value of production) is independent of the legal position if the pricing system is assumed to work without cost.

But the pricing system is not costless

In order to carry out a market transaction it is necessary to discover who it is that one wishes to deal with, to inform people that one wishes to deal and on what terms, to conduct negotiations leading up to a bargain, to draw up the contract …

Once these costs are real, Coase argues, the initial assignment of rights does affect what is produced — and the law, by deciding who holds those rights, helps determine how resources are actually used. This, not the frictionless case, is the paper's deeper and most-often-missed point.