曼昆的经济学定义：Economics is the study of how society manages its scarce resources。
曼昆的经济学十原理中第一条：PEOPLE FACE TRADEOFFS。这一原理的的两段经典举例：
When people are grouped into societies, they face different kinds of tradeoffs.The classic tradeoff is between “guns and butter.” The more we spend on nationaldefense to protect our shores from foreign aggressors (guns), the less we can spendon consumer goods to raise our standard of living at home (butter). Also importantin modern society is the tradeoff between a clean environment and a high level ofincome. Laws that require firms to reduce pollution raise the cost of producinggoods and services. Because of the higher costs, these firms end up earning smallerprofits, paying lower wages, charging higher prices, or some combination of thesethree. Thus, while pollution regulations give us the benefit of a cleaner environmentand the improved health that comes with it, they have the cost of reducingthe incomes of the firms’ owners, workers, and customers.
Another tradeoff society faces is between efficiency and equity. Efficiencymeans that society is getting the most it can from its scarce resources. Equitymeans that the benefits of those resources are distributed fairly among society’smembers. In other words, efficiency refers to the size of the economic pie, andequity refers to how the pie is divided. Often, when government policies are beingdesigned, these two goals conflict.
Efficiency 的定义：the property of society getting the most it can from its scarce resources。
Equity 的定义：the property of distributing economic prosperity fairly among the members of society。
第二条：THE COST OF SOMETHING IS WHAT YOU GIVE UP TO GET IT
第三条：RATIONAL PEOPLE THINK AT THE MARGIN
第四条：PEOPLE RESPOND TO INCENTIVES
第五条：TRADE CAN MAKE EVERYONE BETTER OFF
第六条：MARKETS ARE USUALLY A GOOD WAY TO ORGANIZE ECONOMIC ACTIVITY
第七条：GOVERNMENTS CAN SOMETIMES IMPROVE MARKET OUTCOMES
第八条：A COUNTRY’S STANDARD OF LIVING DEPENDS ON ITS ABILITY TO PRODUCE GOODS AND SERVICES
第九条：PRICES RISE WHEN THE GOVERNMENT PRINTS TOO MUCH MONEY
第十条：SOCIETY FACES A SHORT-RUN TRADEOFF BETWEEN INFLATION AND UNEMPLOYMENT
曼昆经济学原理阅读笔记（二）
市场经济的定义：
market economy - an economy that allocates resources through the decentralized decisions of many firms and households as they interact in markets for goods and services.
曼昆经济学原理阅读笔记（三）
第八条原理：A COUNTRY'S STANDARD OF LIVING DEPENDS ON ITS ABILITY TO PRODUCE GOODS AND SERVICES
“The relationship between productivity and living standards also has profound implications for public policy.
Productivity 定义：the amount of goods and services produced from each hour of a worke's time
Because lower investment today means lower productivity in the future, government budget deficits are generally thought to depress growth in living standards.”
第十条原理：SOCIETY FACES A SHORT-RUN TRADEOFF BETWEEN INFLATION AND UNEMPLOYMENT
“Because prices are sticky, various types of government policy have short-run effects that differ from their long-run effects. When the government reduces the quantity of money, for instance, it reduces the amount that people spend. Lower spending, together with prices that are stuck too high, reduces the quantity of goods and services that firms sell. Lower sales, in turn, cause firms to lay off workers. Thus, the reduction in the quantity of money raises unemployment temporarily until prices have fully adjusted to the change.
The tradeoff between inflation and unemployment is only temporary, but it can last for several years. The Phillips curve is, therefore, crucial for understanding many developments in the economy. In particular, policymakers can exploit this tradeoff using various policy instruments. By changing the amount that the government spends, the amount it taxes, and the amount of money it prints, policymakers can, in the short run, influence the combination of inflation and unemployment that the economy experiences.”
第一个经济学模型：循环流成图（Circular-flow Diagram）
定义：circular-flow diagram - a visual model of the economy that shows how dollars flow through
markets among households and firms.
是资源和货币在市场中循环流动的简单图表。
第二个经济学模型：生产可能性曲线（production possibilities frontier）
定义：a graph that shows the combinations of output that the economy can possibly produce given the available factors of production and the available production technology.
微观经济学（microeconomics）：the study of how households and firms make decisions and how they interact in markets.
宏观经济学（macroeconomics）：the study of economy-wide phenomena, including inflation, unemployment, and economic growth.
曼昆关于人与人之间的相互依赖（Interdependence）关系的精妙描述：
Every day you rely on many people from around the world, most of whom you do not know, to provide you with the goods and services that you enjoy. Such interdependence is possible because people trade with one another. Those people who provide you with goods and services are not acting out of generosity or concern for your welfare. Nor is some government agency directing them to make what you want and to give it to you. Instead, people provide you and other consumers with the goods and services they produce because they get something in return.
可以以这段话为例应用到不同场合来解释我们原本以为需要在形而上层面才能解释的问题。
曼昆经济学原理阅读笔记（五）
比较优势原理
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.
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：
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?
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.
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.
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?
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.
曼昆经济学原理阅读笔记（六）
供给和需求是市场经济运转的动力
概念：
market（市场）：a group of buyers and sellers of a particular good or service.
competitive market（竞争市场）：a market in which there are many buyers and many sellers so that each has a negligible impact on the market price.
理想的竞争市场所需的两个基本特征：
1. the goods being offered for sale are all the same, and
2. the buyers and sellers are so numerous that no single buyer or seller can influence the market price.
市场中的买家和卖家足够多时，才能形成竞争性的市场。反之，市场中卖家只有一两个而买家甚众则必然形成垄断（monopoly），少数卖家可以有足够的力量来左右商品价格，这是最不利于买家的局面。比如中国的电信，铁路，石油行业。为什么国际市场的石油价格上涨时，国内市场会跟着上涨，而在国际市场油价下跌时，我们不会跟着下跌，原因就在这里。
law of demand（需求法则）：Other things equal, when the price of a good rises, the quantity demanded of the good falls. （其他条件相同的情况下，商品价格上涨，则对该商品的需求数量下降。）
quantity supplied（供给法则）：the claim that, other things equal, the quantity supplied of a good rises when the price of the good rises.（其他条件相同的情况下，商品价格上涨时，该商品的供给数量上升。）
law of supply and demand（供需法则）：the claim that the price of any good adjusts to bring the supply and demand for that good into balance.
elasticity and its application（弹性及其应用）
考量影响需求的决定因素时，当提到买家在商品的价格降低，收入提高，替代品（substitute）的价格提高或者互补品（complement）的价格降低的情况下会有更多的对该商品的需求时，此需求分析是定性的而非定量的。要定量的分析需求量相对于其决定因素的改变所作的反应，经济学家引入了“弹性”（elasticity）概念。
elasticity：a measure of the responsiveness of quantity demanded or quantity supplied to one of its determinants.
price elasticity of demand（需求的价格弹性）：a measure of how much the quantity demanded of a good responds to a change in the price of that good, computed as the percentage change in quantity demanded divided by the percentage change in price.
影响需求的价格弹性的一些通用规则：
Necessities versus Luxuries（必需品和奢侈品）：必需品的需求弹性相对于奢侈品要低。即医疗费用增加时人们依然不得不去看病而当游艇价格上涨时会有更多的人决定不买。虽然一样东西属于必需品还是奢侈品取决于购买者的倾向，但衣食住行所需的物品通常可以认为是必需品。
Availability of Close Substitutes（最接近的替代品的可用性）：如果有充分的替代商品，那么人们很容易在一商品价格上涨时转向其替代品，此时其需求弹性较大。
Definition of the Market（市场的定义）：越宽泛定义的市场，其需求弹性越小。因为很难为一个很宽泛定义的物品比如食物找到替代品。
Time Horizon（时间范围）：在较长的时间范围内，商品有更大的需求弹性。
需求的价格弹性公式：Price elasticity of demand =(Q2 - Q1)//(P2 - P1)/
曼昆希望：Throughout this book, however, we only rarely need to perform such calculations. For our purposes, what elasticity represents—the responsiveness of quantity demanded to price—is more important than how it is calculated.
income elasticity of demand（需求的收入弹性）：a measure of how much the quantity demanded of a good responds to a change in consumers’ income, computed as the percentage change in quantity demanded divided by the percentage change in income.
cross-price elasticity of demand（需求的相对价格弹性）：a measure of how much the quantity demanded of one good responds to a change in the price of another good, computed as the percentage change in quantity demanded of the first good divided by the percentage change in the price of the second good.
Cross-price elasticity of demand = Percentage change in quantity demanded of good 1/Percentage change in the price of good 2
这个公式的值的正负取决于两种货物之间是互补的关系还是替代品的关系。
price elasticity of supply（供给的价格弹性）：a measure of how much the quantity supplied of a good responds to a change in the price of that good, computed as the percentage change in quantity supplied divided by the percentage change in price.
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