Basic Economic Concepts
AP Macroeconomics Topic 1 7:30 English narration · English + 中文 subtitles burned in
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Transcript
Here is a result that feels wrong the first time you meet it.
有一个结论，你第一次遇到时会觉得不对劲。
Suppose you are faster than your friend at writing code and faster at writing documentation.
假设你写代码比你朋友快，写文档也比他快， 也就是说你两样都更强。
You are better at both. Should you do both? No.
那你应该两样都自己做吗？
You should still specialise and trade — and both of you end up with more.
不。 你仍然应该专业化并进行交换—— 而且你们两个最后都能得到更多。
Being better at everything does not tell you what to do. What matters is what each hour costs you.
"什么都更强"并不能告诉你该做什么， 真正重要的是每一小时对你意味着放弃什么。
That idea is comparative advantage, and it is the single most tested concept in Unit One.
这个想法就是比较优势， 也是第一单元里最常考的一个概念。
Welcome to Unit One.
欢迎来到第一单元。
Economics begins with scarcity: people's wants are unlimited, but the resources to satisfy them are limited.
经济学从稀缺性开始：人的欲望是无限的， 而用来满足它们的资源是有限的。
Those resources are the four factors of production — land, labor, capital, and entrepreneurship.
这些资源就是四种生产要素—— 土地、劳动、资本和企业家才能。
Know all four by name.
四个都要能叫出名字。
Because resources are scarce, every society must answer three questions: what to produce, how to produce it, and for whom.
因为资源稀缺， 每个社会都必须回答三个问题：生产什么、如何生产、为谁生产。
And every answer forces a trade-off.
而每一个答案都会带来权衡取舍。
Nothing in this course escapes that.
这门课里没有任何东西能逃开这一点。
Opportunity cost is the value of the next-best alternative you give up, and the production possibilities curve puts it on a graph.
机会成本是你放弃的下一个最好选择的价值，而生产可能性曲线把它画在了图上。
The curve shows the maximum combinations of two goods an economy can make when resources are fully and efficiently used.
这条曲线显示：当资源被充分且有效利用时，一个经济体能生产的两种物品的最大组合。
Three kinds of point, and you must read all three.
点有三类，三类你都必须会读。
On the curve: efficient.
在曲线上：有效率。
Inside the curve: inefficient — resources are unemployed.
在曲线内部：无效率——有资源被闲置。
Outside the curve: unattainable.
在曲线外部：无法达到。
The slope of the curve is the opportunity cost.
曲线的斜率就是机会成本。
A straight PPC means constant opportunity cost. And a bowed-out curve means increasing opportunity cost, because resources are not equally suited to both goods.
直线形的 PPC 意味着机会成本不变；而向外凸出的曲线意味着机会成本递增， 因为资源并不同样适合生产这两种物品。
Now, what moves the whole curve?
那么，是什么让整条曲线移动呢？
More resources, or better technology.
更多的资源，或者更好的技术。
That is economic growth, and it shifts the curve outward.
这就是经济增长， 它让曲线向外移动。
Investing in capital goods today is the classic way to do it: you give up consumer goods now to get a bigger curve later.
今天投资于资本品是最典型的做法： 你放弃现在的消费品，换取以后更大的一条曲线。
Be careful with one distinction the exam loves. Moving from inside the curve onto the curve is not growth — that is just employing the resources you already had.
有一个区分要特别小心，考试很爱考： 从曲线内部移动到曲线上，并不是增长——那只是把你本来就有的资源利用起来。
Growth is the curve itself moving out.
增长是曲线本身向外移动。
Back to the hook.
回到开头那个例子。
An absolute advantage in a good means you can simply make more of it.
在某种物品上有绝对优势，意思仅仅是你能生产得更多。
A comparative advantage means you have the lower opportunity cost of making it.
有比较优势，意思是你生产它的机会成本更低。
Those are different questions, and only one of them matters. It is comparative advantage — the lower opportunity cost — that decides who should specialise.
这是两个不同的问题，而只有一个是关键的： 决定谁应该专业化的，是比较优势——也就是更低的机会成本。
A country can have an absolute advantage in everything and still have a comparative advantage in only some things, because opportunity cost is about what you give up, not about how much you can make.
一个国家可以在所有东西上都有绝对优势，却只在部分东西上有比较优势， 因为机会成本讲的是你放弃了什么，而不是你能生产多少。
Let's do the standard question.
我们来做这道标准题。
Country A can make ten wheat or five cloth per day.
A 国每天能生产十单位小麦，或者五单位布。
Country B can make eight wheat or eight cloth.
B 国每天能生产八单位小麦，或者八单位布。
Notice A has the absolute advantage in wheat, and B in cloth — but ignore that and compute opportunity costs.
注意 A 在小麦上有绝对优势， B 在布上有绝对优势——但先把这一点放一边，去算机会成本。
For A, the cost of cloth is ten over five, which is two wheat. For B, it is eight over eight, which is one wheat.
对 A 来说，一单位布的成本是十除以五，等于两单位小麦； 对 B 来说是八除以八，等于一单位小麦。
One is less than two, so B has the lower opportunity cost of cloth. B specialises in cloth.
一小于二，所以 B 生产布的机会成本更低， B 专门生产布。
Now check wheat, and always check it.
现在检查小麦，而且一定要检查。
For A, one wheat costs nought point five cloth. For B, one wheat costs one cloth.
对 A 来说，一单位小麦的成本是零点五单位布；对 B 来说是一单位布。
A gives up less, so A specialises in wheat.
A 放弃得更少，所以 A 专门生产小麦。
The comparative advantages always land on opposite goods.
比较优势总是落在相反的两种物品上。
So they specialise.
所以它们各自专业化。
Now they trade, and there is one condition. Both countries gain only if the terms of trade lie between the two opportunity costs.
接下来是交换，而交换有一个条件： 只有当贸易条件落在两国的机会成本之间时，双方才都能获益。
In our example, A gives up two wheat for a cloth on its own, and B gives up one.
在我们的例子里，A 自己生产时，一单位布要放弃两单位小麦，B 只要放弃一单位。
So any trading rate between one and two wheat per cloth makes both better off.
所以任何介于一到二单位小麦换一单位布之间的交换比例，都会让双方变得更好。
Outside that range, one country would rather produce the good itself.
超出这个范围，就会有一个国家宁可自己生产。
And here is the payoff, the sentence to write in an exam: trade lets a country consume beyond its own production possibilities curve.
这里就是最终的收获， 也是考试要写的那句话：贸易让一个国家能够消费到超出它自己生产可能性曲线的水平。
Not produce beyond it — consume beyond it.
不是生产超出，而是消费超出。
Now the micro tools that the whole course is built on.
现在讲整门课赖以建立的微观工具。
Demand relates price to the quantity buyers will buy.
需求，是价格与买家愿意购买的数量之间的关系。
The law of demand makes the curve slope downward.
需求定律让这条曲线向下倾斜。
Then the distinction that earns and loses more points than any other: a change in the good's own price is a movement along the curve. The determinants shift the whole curve.
接下来是那个得分和失分都最多的区分： 物品自身价格的变化，是沿着曲线移动；而各种决定因素，会让整条曲线移动。
There are five to know — income, tastes, the prices of substitutes and complements, the number of buyers, and expectations.
有五个要记住——收入、偏好、替代品和互补品的价格、买家的数量，以及预期。
Own price, move along. Anything else, shift.
自身价格，沿线移动；其他任何东西，整条曲线移动。
Supply relates price to the quantity sellers will offer, and the law of supply makes it slope upward.
供给，是价格与卖家愿意提供的数量之间的关系，供给定律让它向上倾斜。
Its determinants are input prices, technology, taxes and subsidies, the number of sellers, and expectations.
它的决定因素是投入品价格、技术、税收和补贴、卖家的数量，以及预期。
Same rule, and it never changes: the good's own price moves you along the curve; a determinant shifts the whole curve.
规则完全相同，而且永远不变：物品自身的价格让你沿着曲线移动， 任何决定因素让整条曲线移动。
Notice how taxes and subsidies enter here — a tax raises costs and shifts supply left, a subsidy lowers costs and shifts it right.
注意税收和补贴是从这里进来的—— 税提高成本，使供给左移；补贴降低成本，使供给右移。
Put both curves together and equilibrium is where supply meets demand, clearing the market.
把两条曲线放在一起，均衡就是供给与需求相交的地方，市场在那里出清。
Away from it, the market corrects itself in one of two ways.
离开均衡点，市场会用两种方式之一自我修正。
Above the equilibrium price there is a surplus, and the surplus pushes price down. Below the equilibrium price there is a shortage, and the shortage pushes price up.
在均衡价格之上会出现过剩， 过剩把价格往下压；在均衡价格之下会出现短缺，短缺把价格往上推。
Neither needs anybody to be in charge — the disequilibrium itself creates the pressure that removes it.
这两种情况都不需要任何人来指挥——非均衡本身就产生了消除它的压力。
Finally, what happens when a determinant shifts one curve.
最后，看看某个决定因素让一条曲线移动时会发生什么。
A new technology lowers producers' costs and shifts supply right.
新技术降低了生产者的成本，供给右移。
Read it along the unchanged demand curve: the equilibrium price falls and the equilibrium quantity rises.
沿着没有变化的需求曲线来读： 均衡价格下降，均衡数量上升。
That is the pattern for every single-shift question.
所有"单条曲线移动"的题目都是这个模式。
But now suppose incomes rise at the same time, shifting demand right as well.
但现在假设收入同时上升，需求也右移。
Quantity clearly rises — both shifts push it the same way.
数量显然上升——两次移动都把它往同一个方向推。
But price?
可价格呢？
Supply pushes it down and demand pushes it up.
供给把它往下压，需求把它往上推。
The answer depends on which shift is larger, so price is indeterminate.
答案取决于哪一次移动更大， 所以价格是不确定的。
When both curves shift, one of the two variables is always indeterminate, and naming which one is the mark.
当两条曲线同时移动时，两个变量中总有一个是不确定的， 而说出是哪一个，就是那一分。
Three marks students throw away.
三个学生常丢的分。
First, comparative advantage means the lower opportunity cost — never absolute advantage.
第一，比较优势指的是更低的机会成本——绝不是绝对优势。
Compute both goods' costs and write the ratio down; do not guess from who produces more.
两种物品的机会成本都要算出来并写下比值，不要根据"谁产得多"去猜。
Second, before you touch a graph, decide whether the change is a movement or a shift: own price moves you along, anything else shifts the curve.
第二，在动图之前先判断这个变化是"沿线移动"还是"整条曲线移动"： 自身价格让你沿线移动，其他任何东西都让曲线移动。
Third, on the free-response section, draw the graph, label both axes and both curves, and label the new equilibrium.
第三，在自由作答部分，一定要把图画出来，标好两条轴和两条曲线，并标出新的均衡点。
The same shift logic drives the aggregate models later in this course, so the habits you build here are the ones you will be graded on all year.
同样的移动逻辑会驱动这门课后面的总量模型， 所以你在这里养成的习惯，会被评分一整年。