P1 P2-经济学十大原理

How people make decision

1. People face tradeoffs.

人们面临得失交换，权衡取舍。To get one thing,we usually have to give up another thing. 在某一方面得到意味着另一方面失去。There is no such thing as a free lunch.--天下没有免费的午餐。

2. The cost of something is what you give up to get it.

经济学是一门研究行为的科学，研究选择的科学。将一个选择与其他的选择做比较。你选择上这门课，意味着你放弃了在这个时间里上其他课。选择是一个集合。某个政策给带来百万收益，质问如果投资到其他领域呢，收益是否更大。

The opportunity cost of an item is what you give up to obtain that item.

为什么广东出现民工荒？有更好的选择了，粮价提高了，种地收益更大，所以打工的机会成本高了。

为什么老虎伍兹中途退学？在外面打球的收益很大。

3. Rational people think at the margin.

理性人思考边际量。导数。一般人看平均量。

people make optimal decisions by comparing costs and benefits at the margin. 人们做最优决策时比较成本和收益。margin指的是增量的增长。

Marginal changes are small, incremental adjustments to an existing plan of action. 边际变化是对已有行动计划的小的、增量调整。 .吃不吃饭不需要做决策，需要决策的是多吃一口还是少吃一口，这就是margin.

为什么航空公司让雇员和他们的亲属在乘客上完后可以免费搭乘？

--- 边际成本与平均成本。marginal cost vs. average cost. 因为这样边际成本很低，免费乘机的雇员们只需要一杯水。

4. People respond to incentives.

人们会对激励做出反应；

How people interact. 人们如何相互作用

5. Trade can make everyone better off. 贸易能使人人受益

6. Markets are usually a good way to organize economic activity.

7. Governments can sometimes improve market outcomes. 政府有时可以改进市场结果；

How the economy as a whole work

8. The standard of living depends on a country's production. 一国的生活水平取决于它的生产。

9. Prices rise when the government prints too much money.

10. Society faces a short-run tradeoff between inflation and unemployment. --社会面临通货膨胀和失业之间的短期得失交换。