经济学 1968

公地悲剧

加勒特·哈丁

人人可用、无人拥有之物，会被每个理性的人一同用到枯竭。

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In depth · the introduction

为什么一片公共渔场会被打捞一空，私家鱼塘里的鱼却不会？

核心想法

有些东西属于所有人、又不属于任何一个人——全村共用的一块草场、一处渔场、那片开阔的空气。哈丁的论断令人不安：这些共享之物往往会被毁掉，毁掉它们的不是恶人，而是做着合情合理之事的普通人。我若往公共牧场多放一头牛，这头牛的好处全归我；而草被多啃的损耗，却由大家分摊。于是「再多放一头」永远是聪明之举——既然人人都一样聪明，草便被啃成了光秃秃的泥地。

他把这称作「公地悲剧」，并主张它「没有技术解」：再巧的围栏或化肥，也修不好一个根植于激励本身的问题。真正的解药，都在于改变「谁、以何种方式」取用资源的规则。

它是如何诞生的

哈丁是加州大学圣巴巴拉分校的生态学家。1968 年，他把一场学会主席致辞改写成一篇短文，发表在《科学》杂志上。他写作的背景，是战后人口的激增与方兴未艾的环保运动——蕾切尔·卡森的《寂静的春天》六年前刚刚问世——而他真正忧心的，是人口的增长，他视之为隐在污染与匮乏背后的那个公地问题。牧场，是他让这套逻辑令人难忘的方式；它奏效了：这一语脱口而出，进入了日常用语，成为现代科学中被引用最多的观念之一。

它为何重要

它给一个无处不在的问题起了名字、配了图画——凡是人们共享某种难以围起来的东西，这问题就会冒头：被过度捕捞的海洋、被抽干的含水层、被污染的河流，以及如今这片人人都可往里排碳、却正在变暖的大气。一旦你看清了这结构，便可去寻药方——而药方几乎从来不是「再努力些」或「别那么贪」，而是改变规则：所有权、配额、许可，或带有牙齿的共同约定。

一个可以想象的画面

想象一家自助餐厅，账单由在场所有人平摊。你多取的每一盘都美味、且对你几乎免费——成本被抹匀到整桌人身上。于是人人都点过了头，食物告罄，共担的账单却越滚越大。要是这顿饭只由你自己买单，你点起来便会有分寸。差别不在你的品性，而在「下一盘由谁付钱」。

它的位置

哈丁的悲观，是一场漫长争论的一极。托马斯·马尔萨斯（1798，见本馆）曾警告：人口的增长会超过资源；哈丁则为污染的时代更新了这份忧虑。争论的另一极，站着埃莉诺·奥斯特罗姆（1990，也在本馆）——她实地走访，找到了把公地可持续治理了数百年的社群，表明毁灭是一种风险，而非宿命。在亚当·斯密对市场的信念，与「需要国家」的主张之间，公地标出了二者都可能照拂不到的那片地带。

The original document

Original source text

Garrett Hardin · Science, New Series, Vol. 162, No. 3859 (13 December 1968), pp. 1243–1248 · based on a presidential address to the Pacific Division of the AAAS, Utah State University, Logan, 25 June 1968.

The summary

Hardin opens by arguing that some problems admit no technical fix — no improvement in technique or yield will solve them, because the difficulty is one of values, not of means.

The population problem has no technical solution; it requires a fundamental extension in morality.

The pasture

To show why, he draws a now-famous picture of a grazing common shared by many herdsmen.

Picture a pasture open to all.

Each herdsman, he argues, rationally asks one question — and the arithmetic always points the same way:

What is the utility to me of adding one more animal to my herd?

The gain from the extra animal is his alone (a benefit of nearly +1); the cost — overgrazing — is shared among all the herdsmen (a fraction of −1). So the rational herdsman adds another animal, and another. Since each reasons alike, the conclusion is collective.

Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit—in a world that is limited.

Ruin is the destination toward which all men rush, each pursuing his own best interest in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all.

From pasture to pollution and population

Hardin extends the same logic to pollution (the commons as a sink into which each discharges waste) and, centrally, to human population growth, which he regarded as the commons problem behind all the others. His remedy is not appeals to conscience — which he holds to be self-eliminating — but agreed-upon constraint, “mutual coercion, mutually agreed upon by the majority of the people affected.”

The remedy — and its shadow

Applied to population, Hardin reaches a conclusion many readers have since rejected:

Freedom to breed is intolerable.

(On honesty: Hardin’s later writing on population, immigration and aid carried coercive and, at times, explicitly racist views; this line is quoted not to endorse it but because the essay’s reception cannot be understood without it — see the Expert “limits” section.)

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Garrett Hardin · University of California, Santa Barbara · Science · 13 December 1968