亲爱的经济学家：

Dear Economist,

我自己偶尔会买点焰火来放，产生令人愉悦的正外部性。不幸的是，外行放焰火有时会造成悲剧——而且经常有人说要禁止私放焰火。怎样才能经济有效地应对这种负外部性呢？

Occasionally, I buy and launch my own fireworks, generating cheerful positive externalities. Sadly, some amateur launchings end in tragedy – and there is frequent talk of a private firework ban. What is the economically efficient way of dealing with those negative externalities?

延斯?弗勒利克?霍尔特(Jens Frolich Holte)，挪威

Jens Frolich Holte, Norway

亲爱的延斯：

Dear Jens,

如果你对问题的诊断是正确的，那我们就可以从教科书中寻找解决方案。科斯定理(Coase theorem)告诉我们，从原则上说，在交易成本为零的市场上，根据邻居是欣赏你的焰火表演还是害怕受到伤害，他们可以付钱给你，让你燃放（或是不放）焰火。

If you’ve diagnosed the problem correctly, we can reach for a textbook solution. In a market with zero transaction costs, Coase theorem tells us that your neighbours could, in principle, pay you to hold firework displays, or not to, depending on their enjoyment of the spectacle or fear of injury.

更为可能的是，我们需要一个与科斯解决方案类似的办法，可以对焰火征收“外部性税”以反映风险，或提供补贴以反映其带来的好处。但我不确定，在这个问题上，你对正外部性或负外部性的判断是否正确。

More likely, we would need to approximate the Coasian solution with an externality tax on fireworks (to reflect the risks) or a subsidy (to reflect the benefits). But I am not sure you have correctly identified the positive and negative externalities here.

除非你朝着街道放焰火，否则，多数风险必然由你和你那些选择近距离欣赏焰火表演的朋友承担。

Unless you are shooting the fireworks down the street, most of the risk is surely borne by you and your friends, who’ve chosen to enjoy the display at close range.

这就不存在负外部性的问题，因为他们对风险是知情的。

There is no negative externality there: they’ve knowingly taken the risk.

就正外部性而言，我怀疑那些不知道焰火表演将何时开始的远邻，是否会如你所想的那样欣赏焰火表演。而且，噪音可能会让他们颇为恼火。

On the positive externality side, I doubt that more distant neighbours enjoy the show as much as you think, not knowing when it is going to start. And they may be aggravated by the noise.

总体而言，外部性是什么呢？

On balance, where are the externalities?

实际上，我们应该关注于如何鼓励人们更负责任地使用焰火。如果你的焰火表演伤害了无辜的人，你就应当负起责任。适当评估可能的伤害水平，会鼓励你在放焰火时更加当心。

We should focus instead on encouraging more responsible use of fireworks. If your firework display hurts an innocent, you should be liable. An appropriate level of likely damages will encourage you to take exactly the right amount of care with your displays.