为了让读者深入了解为什么选择实在是痛苦—让我们回到我们之前提到的例子，某人让你在士力架巧克力棒与一包M&Ms的产品之间做个选择。假设，作为讨论的前提，你拿了M&Ms。根据曼昆的原理，那些M&Ms的成本是你为了得到M&Ms所放弃的士力架巧克力棒。此情况下你的收益就是—经济学家所说的“经济利润”—即你获得M&Ms(比如0.75美元)的价值与你失去士力架巧克力棒的价值(比如0.40美元)之间的价差。换句话说，你的经济利润只有0.35美元。虽然你估计M&Ms的价值为0.75美元，而选择士力架巧克力棒让你的收益少了0.40美元

　　Indeed, the more choices you have, the worse off you are. The worst situation of all would be somebody coming up to you and offering you a choice between two identical packages of M&Ms. Since choosing one package (which you value at $.75) means giving up the other package (which you also value at $.75), your economic profit is exactly zero! So being offered a choice between two identical packages of M&Ms is in fact equivalent to being offered nothing.

　　事实上，你拥有越多的选择，你的状况更加糟糕。最糟糕的情况是某人让你从相同的M&Ms做选择。选择其中一个(你估计价值为0.75美元)意味着放弃另一个(你估计价值也为0.75美元)，你的经济利润恰好为0!因此在两个相同的M&Ms上做选择事实上等同于没有选择。

　　Now, a lay person might be forgiven for thinking that being offered a choice between two identical packages of M&Ms is in fact equivalent to being offered a single package of M&Ms. But economists know better. Being offered a single package of M&M effectively means having to choose between a package of M&Ms (which you value at $.75) and nothing (which you value at $0). Choosing the M&Ms gives you an economic profit of $.75, which is $.75 more than your economic profit when you are offered a choice between two identical packages of M&Ms.

　　现在，外行的人可能不会想到，提供两个相同的M&Ms让你选择其实等同于让你选择一个M&Ms。但经济学家考虑的更周全。提供一个M&Ms实际上意味着让你在一包M&Ms(你估计价值为0.75美元)和什么也没有之间做选择(你估计价值为0美元)。选择M&Ms可以给你0.75美元的经济利润，比你在两个相同的M&Ms做选择所获得的经济利润多0.75美元。

　　At this point it is worth acknowledging that (1) there may be readers who have failed to grasp the above subtleties in their entirety, and (2) such readers may well be beginning to wonder whether they are, in a word, stupid. Any lingering doubts should be eliminated by the Mankiw's

　　在这点上值得承认的是(1)可能有些读者不能从整体上理解以上巧妙之处，及(2)这些读者也许开始会认为自己是不是很愚蠢，任何悬而未决的疑问都应该用曼昆的原理来解决。

　　Principle #3: Rational people think at the margin

　　原理 3 理性人考虑边际量

　　Translation: People are stupid

　　解释 人们是愚蠢的

　　One point that is immediately obvious to the most casual observer with the meanest intelligence is that most people do not think at the margin. For example, most people who buy oranges at the grocery store think like this: “Hmmm, oranges are $.25 each. I think

　　I'll buy half a dozen.” They do not think like this: “Hmmm, oranges are $.25 each. I'm going to buy one, because my marginal value exceeds the market price. Now I'm going to buy a second one, because my marginal value still exceeds the market price...” We know most people don't think like this because most people don't fill their shopping baskets one orange at a time!

　　智商最低的随机观测者都能很明显地知道多数人并不考虑边际量。例如，多数人在杂货店买桔子时他们都是这样想：“嗯，桔子每个0.25 美元。我要六个。”而不是“嗯，桔子每个0.25美元。我要去买一个，因为我的边际价值超过了市场价格。现在我要买第二个，因为我的边际价值仍然超过市场价格。”我们知道多数人认为并不是那样因为多数人不会在他的购物中一次装一个桔子。

　　But we are now led inexorably toward a most unhappy conclusion. If—as Mankiw says—rational people think at the margin, and if—as we all know—most people do not think at the margin, then most people are not rational. Most people, in other words, are stupid. Hence my translation of the third principle of economics: People are stupid.

　　但现在将引导我们无情地推出这个最让人难过的结论。如果—如曼昆所说的—理性人考虑边际量，接着如果—如我们所知道的—多数人认为不会考虑边际量，因此可以说多数人是不理智的。换句话说，多数人是愚蠢的。因此我对第三个原理的解释为：人们是愚蠢的

　　Before sinking into despair for the fate of the human race, however, the reader would be wise to consider Mankiw's

　　然而，在对人类命运感到绝望之前，读者会理智地考虑一下曼昆的原理

　　Principle #4: People respond to incentives.

　　原理4人们会对激励作出反应

　　Translation: People aren’t that stupid.

　　解释 人们也不是那么愚蠢

　　The dictionary says that incentive, n., is 1. Something that influences to action; stimulus; encouragement.

　　Incentive(激励)在词典的解释为，1.影响行动的因素;促进因素;鼓励

　　So what Mankiw is saying here is that people are motivated by motives, or that people are influenced to action by things that influence to action. Now, this may seem to be a bit like saying that tautologies are tautological—the reader may be thinking that people would have to be pretty stupid to be unmotivated by motives, or to be inactive in response to something that influences to action. But remember Principle #3: People are stupid. Hence the need for Principle #4, to clarify that people aren’t that stupid.

　　因此如曼昆所说人们会被动机激发，或人们受影响行动的行动影响。现在你可以那句话是同义重复—读者也许会认为人们是多么愚蠢若他们不会对激励做出反应，或对影响行动的激励纹丝不动。记住原理3是：人们是愚蠢的。因此对于原理4，有必要澄清：人们并不是那样的愚蠢

　　Only truly stupid people can fail to understand my translation of Mankiw's

　　只有真正愚蠢的人才不能理解我对曼昆原理的解释

　　Principle #5: Trade can make everyone better off

　　原理5 贸易能使每个人的状况变得更好

　　Translation: Trade can make everyone worse off

　　解释 贸易能使每个人的状况变得更坏

　　But, the reader may well be asking, isn't the translation of the fifth principle the exact opposite of the principle itself? Of course not.

　　然而，读者可能会问，难道第五个原理的解释真的是与原文相反的?当然不是。

　　To see why, first note that "trade can make everyone better off" is patently obviously: if I have a Snickers bar and want M&Ms and you have M&Ms and want a Snickers bar, we can trade and we will both be better off. Surely Mankiw is getting at something deeper than this? Indeed, I believe he is. To see what it is, compare the following phrases:

　　要找出原因，首先要注意“贸易能使每个人的状况变得更好”是显而易见的：如果我有个士力架巧克力棒想要M&Ms而你有M&Ms想要士力架巧克力棒，我们可以贸易且我们的状况会更好。在这句话上，曼昆有更深的理解吗?事实上，我认为是，为了解释这句话，对比以下两个短语：

　　A: Trade can make everyone better off

　　A: 贸易能使每个人的状况变得更好

　　B: Trade will make everyone better off

　　B: 贸易会使每个人的状况变得更好

　　Now, Statement B is clearly superior to Statement A. Why, then, does Mankiw use Statement A? It can only be because Statement B is false. By saying that trade can make everyone better off, Mankiw is conveying one of the subtleties of economics: trade can also not make everyone better off. It is a short hop from here to my translation, “Trade can make everybody worse off.” (A numerical example can be found in this footnote.3)

　　The subtlety evident in Principle #5 is even more clearly visible in the next two principles.

　　现在，B句明显强于A句。那为什么曼昆使用A句呢?可能的原因只有B句是错的。通过“贸易能使每个人的状况变得更好”，曼昆传递了经济学中的巧妙之处：贸易也不能使每个人的状况变得更好。这与我的解释很接近，“贸易能使每个人的状况变得更坏。”

　　原理5显见的微妙之处在以下的两个原理里更能体现出来。

　　Principle #6: Markets are usually a good way to organize economic activity

　　原理6市场通常是组织经济活动的一种最好方法

　　Translation: Governments are stupid.

　　解释政府是愚蠢的

　　Principle #7: Governments can sometimes improve market outcomes

　　原理7 政府有时可以改善市场结果

　　Translation: Governments aren’t that stupid.

　　解释：政府也不是那样的愚蠢

　　To see the key role that Principle #5 plays in both of these statements, note that the original phrasing of Principle #5 (“Trade can make everyone better off”) leads to Principle #6 (“Governments are stupid”). After all, if trade can make everyone better of what do we need government for? But the translation of Principle #5 (“Trade can make everyone worse off”) leads to Principle #7 (“Governments aren’t that stupid”). Afte