經濟學 1960

社會成本問題

羅納德·寇斯

當討價還價無成本，法律只決定誰付錢——而非生產什麼。

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In depth · the introduction

該讓污染者付錢，還是受害者？寇斯的答案出人意料：當雙方可以自由討價還價時，這並不會改變究竟生產出什麼——改變的只是誰來開支票。

核心想法

我們通常把污染或妨害看作「一方傷害另一方」，於是去問該如何約束那個肇事者。寇斯說，這個框架本身就錯了。損害是雙向的：踩壞農夫莊稼的牛群，與想要那些莊稼的農夫，不過是兩個人為不同的用途，想要同一塊地。攔住牛群，傷害的是牧場主；放牛去吃，傷害的是農夫。明智的問題是：哪一種用法更值錢。

接著是那個驚人之處。設想兩人能交談、能無成本地達成交易。寇斯證明：無論法律是否要牧場主為損害買單，他們最終都會養下恰好正確的牛數——那個讓肉與莊稼的總價值最大的數目。若牧場主不必擔責，農夫會付錢請他少養幾頭；若牧場主須擔責，他會自己少養幾頭。無論哪種，牛群一樣多。法律決定的是誰最終更富，而不是究竟做了什麼。

它是如何誕生的

羅納德·寇斯是一位英國經濟學家，長於注意到別的經濟學家假定掉的東西。在 1959 年一篇論無線電頻譜的文章裡，他主張應把電波當作財產來拍賣——並順帶拋出一句：在自由討價還價下，誰先拿到電波其實無關緊要。芝加哥的經濟學家們以為他犯了錯。

於是他們請他到阿倫·迪雷克托家中赴宴，想糾正他。傳說那一屋子人——米爾頓·傅利曼、喬治·斯蒂格勒等——入席時堅信寇斯錯了，散席時卻被說服他是對的。他們催他把它寫出來；成果便是這篇 1960 年的論文。它把他帶到了芝加哥大學，並在三十年後，把他帶向了諾貝爾獎。

它為何重要

寇斯悄然拆掉了那個條件反射：似乎每一樁損害都需要政府課稅或下禁令。在人們能討價還價之處，他們往往能自己擺平，而法律的職責，不過是把可供交易的權利界定清楚。但是——這才是他真正、卻常被遺忘的要點——討價還價通常並非無成本。當達成交易很難時，法律把權利判給誰，便確實決定了會發生什麼。這一洞見，催生了一整個把法律與制度當作經濟機器來研究的領域。

一個可以想像的畫面

想像兩個室友，一個愛打鼓，一個需要安靜念書。共享的空氣這份「權利」，無論歸打鼓的還是歸念書的，只要他們能商量，就會落在同一個安排上——比如，晚上八點前可以打鼓——因為那是對他們倆合起來最值錢的安排；他們只需互讓個人情、或貼點房租，把它定下來。規則決定的是誰欠誰一份人情，而不是這一晚究竟怎麼過。寇斯真正要問的是：當「商量」本身代價太高時，會怎樣——那時，規則便決定了一切。

它的位置

在寇斯之前，教科書對外部性的解法是亞瑟·庇古的：對損害課稅。寇斯證明，這稅既非理所當然、也並非總是對的。在他之後，法律經濟學這一領域興起，還有「總量管制與交易」這個務實的點子——創造出可交易的排污權，讓市場把它挪到最能發揮作用之處。它與本館中其他關於公地的難題並立：加勒特·哈丁的「公地悲劇」點出了問題，而埃莉諾·奧斯特羅姆則展示了：社群往往無需市場、也無需國家，就能治理好共享的資源。它們共同勾勒出：亞當·斯密那隻看不見的手會在何處失靈——以及我們能為此做些什麼。

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.