（法理词典翻译）科斯定理
The Coase Theorem科斯定理
Ronald Coase是芝加哥大学“法与经济学”系成员也是诺贝尔经济学奖得主。我们在这里称之为科斯定理的理论是在下面这篇家喻户晓的论文中提出的：
Ronald Coase is a member of the law and economics faculties at the University of Chicago and a winner of the Nobel Prize in Economics. The idea that we call the Coase Theorem was advanced in a very famous paper:
R.H. 科斯，社会成本问题，法与经济学期刊 3，1-44 (1960)。
Coase, , The Problem of Social Cost, Journal of Law and Economics 3, 1-44 (1960).
为了理解科斯定理，我们首先得介绍另一个概念，就是外部性。简单地讲，经济学上的外部性就是经济行为带来对参与经济行为中的个人或厂商产生影响的成本。这里有个例子：
To understand the Coase theorem, we first need to introduce another idea, the externality. Roughly speaking, an economic externality is cost imposed by an activity that is not accrued by the person or firm who engages in the activity. Here's an example:
Reading铁路公司的从农夫Jones的农田中间穿过。机车溅出的火花点燃了作物，导致Jones农作物的损失，使得Jones承担了100美元的成本。这个成本就是外部性。
The Reading Railroad has track that goes by Farmer Jones's farm. The locamotives cast off sparks that cause a fire that damages Farmer Jones's crop, imposing a cost on Jones of $100. That ocst is an externality.
如果Reading铁路公司拥有这片农田，那么它将承担这个成本，也就意味着将不再有外部性了。在Coase之前，我们总是认为外部性的存在证立了某些政府干预的合理性。例如，我们可以设立一条责任分配的规则，要求Reading铁路公司赔偿作物的损失。如果没有这种规则，那么即使铁路公司可以有效率地防止作物损失，它也就不会有防止损害的激励。让我们为这个假想案例再增添一些内容：
If the Reading Railroad owned the farm, then it would bear the cost, and there wouldn't be an externality. Before Coase, we thought that the existence of externalities justified some kind of government intervention. For example, we could create a liability rule that required the Reading Railroad to pay for the damage to his crops. Without a liability rule, the railroad wouldn't have any incentive to prevent the damage if there was a cost-effective means of doing so. Let's add a fact to our hypothetical:
Reading铁路公司可以购买并安装价值50美元的百分之百有效的阻火器。
The Reading Railroad can purchase and install a 100% effective spark arrestor for $50.
我们要求铁路公司安装50美元的阻火器来防止100美元的损害。在Coase之前，我们会说“将外部不经济内部化！”我们用侵权法将铁路带来的外部成本转化为内部成本。
We want the railroad to install the spark arrestor for $50 to prevent $100 worth of damage. Before Coase, we said, \"internalize the external diseconomies!\" Really! That is, use tort law to transform the external cost imposed by the railroad into an internal cost.
这就是Coase的切入点。然而为了理解Coase说了啥，我们还需要学一点点经济学术语。当我们说到“交易成本”的时候，我们是指达到交易的成本。在真实世界中，律师费用常常是交易成本的一部分，但是为了成交所花费的时间和金钱也属于交易成本——即使您实际上没有花费现金。再进一步，倘若我们假设零交易成本——不必花费时间与精力，不用请律师，甚至不用签署什么书面材料。
This is where Coase came in. But to understand what Coase said, we need to add another bit of economic jargon. By transaction cost, we mean the cost of reaching a bargain. In the real world, lawyers are frequently part of transaction costs, but the time and expense that it takes to strike a deal are transaction costs as well--even if you don't actually lay out any cash. One more little move, if we assume that there are zero transaction costs, we are simply assuming that it costs absolutely nothing to strike a deal--no time, no effort, no lawyers, not even any paper on which to write it up.
Coase如是说，“让我们假设零交易成本！”好的，那么接下来如何！如果我们假设零交易成本，在存在外部性的情况下，不管初试权利授予何方，市场总是会达到最有效率的结果。让我们再次回到假设来：
Coase said, \"Let's assume zero transaction costs!\" Okey dokey, what next! If we assume zero transaction costs, then when there are externalities, the market will reach the efficient outcome irrespective of how entitlements are assigned.Let's go back to our hypo:
假设零交易成本，不管法律将制造火花的权利授予铁路，还是将免于火花侵扰的权利授予农民，结果都是一样的。为什么呢？让我们来看看。这里有两种可能性：
Assuming zero transaction costs, it doesn't matter whether the law assigns the right to generate sparks to the railroad or the right to be free from sparks to the farmer. Why not? Let's work it out. There are two possibilities:
如果将权利授予农民，那么铁路因为侵犯了免于火化侵扰的权利，而向农民赔偿损害支付100美元。铁路将意识到，它可以通过投资50美元购买阻火器来省下这100美元。所以铁路将购买阻火器。
If we assign the entitlement to the farmer, the railroad will pay $100 in damages to the farmer for vioalting the farmer's right to be spark free. The railroad will realize that it can save this $100 cost by investing $50 in a spark arrestor. So the railroad will buy the spark arrestor.
如果将权利授予铁路，农民将承担火灾带来的100美元成本。农民将会意识到，他可以支付50美元（加上某些额外的费用，假定共计51美元）给铁路，作为交换，铁路将安装50美元的阻火器。由于我们假设了零交易成本，所以铁路和农民都从这笔交易中获利。
If we assign the entitlement to the railroad, the farmer will incur $100 in costs from the fire. The farmer will realize that he can save this $100 cost by entering into a contract whereby he pays $50 (plus some extra enducement, say $51 total) to the railroad in exchange for the railroad installing the spark arrestor. Since we have assumed zero transaction costs, the railroad and the farmer both benefit from this deal.
这就是了！不管将权利授予何方，我们都将得到最有效率的结果。
That's it! It doesn't matter whether we assign the right to the farmer or the railroad. Either way, we get the efficient outcome.
如果你是法学一年生，科斯定理将是理解侵权法的经济学的有力分析工具。当你学习一个新的问题或者新的规则的时候，问一下自己，“如果在零交易成本的情况下，这个问题将会怎么样？”然后接着问，“如果假设存在交易成本又会如何？”
If you are a first year law student, the Coase theorem is a very powerful analytic tool for understanding the economics of tort law. When you study a new rule or problem, ask yourself, \"How would this come out assuming zero transaction costs?\" Then ask, \"If we assume positive transaction costs, how does the problem change?\"
提醒一句，“零交易成本”假设仅仅是一个假设。在真实世界中，总是（或通常总是）有交易成本的。尽管如此，在某些情况下，交易成本相当低，所以有效率的交易是可以达到的。在另一些情况下，却并非如此。这就是诉讼的来源！
One word of warning, the zero-transaction-costs assumption is just an assumption. In the real world, there are always (or almost always) transaction costs. Nonetheless, in some situations, transactions costs are sufficiently low so that the efficient bargain can be struck. In other situations, this is not the case. That's where the action is! 由科斯的一些经历可知
1、一个人的创新力强的时期就那么几年。
2、一个人作品不在多，而在精。
3、作品少更需要别人赏识，需要一个高水平的学术群体。
4、最有影响力的创新源自年轻人，不重视年轻人就是糟蹋学术的未来。
5、多学科的背景对于学术创新而言具有决定性作用。所以，思维的活跃性代表了学术的潜力。
6、对第3点更进一步的发挥是：出名需要好的学术环境，一个有潜力的圈子，需要高手来理解你的学说并发挥之。
7、从一开始要充满学术批判精神，只有批判才会让你眼睛更亮。
8、社会科学方面，经验是你最好的老师，观察其实更是一种学术方式（如张五常）。
9、最为重要的，要相信自己。
以上几条对科斯定理无阐发，其实经济学对法学的影响没有想象中那么大。法是一门正义的学问，它从根本上是不能定量的。定量只能提供一种现象。
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