<BR>比较优势原理<BR>概念：Absolute Advantage(绝对优势): the comparison among producers of a good according to their productivity.opportunity cost(机会成本): whatever must be given up to obtain some item.comparative advantage(比较优势): the comparison among producers of a good according to their opportunity cost.<BR>机会成本和比较优势之间的差异造就了贸易上的收益。曼昆的例子：<BR>SHOULD TIGER WOODS MOW HIS OWN LAWN?Tiger Woods spends a lot of time walking around on grass. One of the most talentedgolfers of all time, he can hit a drive and sink a putt in a way that most casualgolfers only dream of doing. Most likely, he is talented at other activities too. For example, let’s imagine that Woods can mow his lawn faster than anyone else. But just because he can mow his lawn fast, does this mean he should?<BR>To answer this question, we can use the concepts of opportunity cost and comparativeadvantage. Let’s say that Woods can mow his lawn in 2 hours. In that same2 hours, he could film a television commercial for Nike and earn $10,000. By contrast,Forrest Gump, the boy next door, can mow Woods’s lawn in 4 hours. In thatsame 4 hours, he could work at McDonald’s and earn $20.<BR>In this example, Woods’s opportunity cost of mowing the lawn is $10,000 andForrest’s opportunity cost is $20. Woods has an absolute advantage in mowinglawns because he can do the work in less time. Yet Forrest has a comparative advantagein mowing lawns because he has the lower opportunity cost.<BR>这算是比较优势原理在微观经济学领域应用的例子。比较优势一定是存在的，所以人们只要从事相互间的交易，就一定能从中相互得利。在自由贸易的条件下，人们的商业贸易往来，只有一方得利的情形是罕见的。这就是为什么经济学家们要一致主张自由贸易的原因，这也是为什么我们的国家要积极的参与世贸组织的谈判，争取加入 WTO 的原因。加入 WTO，意味着与他国贸易往来时，双方都会降低或免去进出口关税，消除贸易壁垒，从而使商品的价格降低，最终使两国的消费者得利。而使消费者能够买到尽可能价格低的商品，则是商业的根本目的。<BR>斯密在其《国民经济的性质和原因的研究》中以英国为例在这方面的分析很经典。比如ZF的某些看似聪明的为保护本国某项商品而设置高关税，借以阻止外国廉价质优的同类商品进来，以为是保护了本国人民的利益。但实际上呢，一来这种关税抬高了商品的价格，而使消费者不得不多掏腰包，二来这种保护实际上是仅使国内生产该商品的商人得利，并且在这种情况下他们会设法持续提高高价质劣的此种商品给消费者，从而长期损害消费者的利益。<BR>富国与穷国的贸易，在自由公平的贸易条件下，不见得是穷国受损害，相反，因为比较优势原理，是双方互惠的。伍兹和其邻居小孩的例子很好的说明了这一点。无论如何，有需求才会有贸易。如果我们国内的消费者有需要购买美国商品的需求，那么就有使这一交易自由进行的必要。可以假设，如果一个国内消费者希望购买一部手机，而在他面前只有两种选择，一种是性能差的国货，一种是性能好的外国货，那么出于保护该国货的目的而提高对外国手机的关税的做法以阻止消费者购买外国手机的行为就是对消费者的利益的侵犯。这样的行为除了使消费者多掏了腰包外，并没有给国家和社会带来什么特别的好处。因为外国手机如果和中国手机一样在中国卖，交同样的税给中国ZF，那么保护国产手机企业的意义在何处？仅仅是让生产手机的商人得利！另外一种情况，国家为扶持某些被认为有前途的行业而向该行业注入资金或奖励金的做法，也与此类似，是养肥了少数人而损害了多数人利益的愚蠢行为。在市场中，资源自然会流向那些有利可图的行业，没有利益的行业资本自然不会进入，何须外力介入。ZF的扶持和奖励的做法，除了使该行业的少数人获利并损害了纳税人的利益之外，没有更积极的意义。<BR>正如现在美国ZF经常祭出的对华纺织品反倾销政策，就是一个对美国消费者来说有损害的政策。因此最多也只是嚷嚷一下而已，不能长期有效地实行下去。该政策在其他政治领域的作用，才是其目标所在。但是这等于要美国民众来负担这份额外的政治成本。<BR>曼昆的结论：The principle of comparative advantage shows that trade can make everyone betteroff. You should now understand more fully the benefits of living in an interdependenteconomy. But having seen why interdependence is desirable, you mightnaturally ask how it is possible. How do free societies coordinate the diverse activitiesof all the people involved in their economies? What ensures that goods andservices will get from those who should be producing them to those who shouldbe consuming them?<BR>In a world with only two people, such as the rancher and the farmer, the answeris simple: These two people can directly bargain and allocate resources betweenthemselves. In the real world with billions of people, the answer is lessobvious. We take up this issue in the next chapter, where we see that free societiesallocate resources through the market forces of supply and demand.<BR>