The Fundamental Economic Problem
A-Level Economics Topic 1 20:01 English narration · English + 中文 subtitles burned in
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Transcript
Think of everything you want.
想一想你想要的一切。
A better phone. More free time.
更好的手机。
Now think of what the world actually has: a fixed amount of land, a fixed number of workers, and only twenty-four hours in a day.
更多的空闲时间。 再想想世界真正拥有的： 有限的土地、有限的劳动者，一天也只有二十四小时。
Wants are unlimited. Resources are finite.
欲望是无限的，资源是有限的。
That gap never closes — and every question in economics grows out of it.
这个缺口永远无法消除——经济学中的每一个问题，都由它而来。
Today we lay the foundation of the whole subject.
今天我们来打好整门学科的基础。
Scarcity and choice.
稀缺与选择。
Opportunity cost.
机会成本。
The factors of production.
生产要素。
The economic systems.
经济体制。
The production possibility curve.
生产可能性曲线。
And the types of good.
以及物品的类型。
Let's begin.
让我们开始吧。
This gap has a name: the economic problem.
这个缺口有一个名字：经济问题。
Resources are finite — there is only so much land, labour and capital.
资源是有限的——土地、劳动和资本都只有那么多。
Wants are unlimited — people always want more.
欲望是无限的——人们总想要更多。
So everything useful is scarce, and every society must answer the same three questions.
所以一切有用的东西都是稀缺的， 每个社会都必须回答同样的三个问题。
What to produce?
生产什么？
How to produce it?
怎样生产？
And for whom?
为谁生产？
Resources are the things we use to make what people want.
资源是我们用来生产人们想要之物的东西。
From those resources we make two kinds of output.
用这些资源，我们做出两类产出。
Goods are things you can touch — food, clothes, a phone.
物品是能摸到的东西——食物、衣服、手机。
Services are work done for you — a haircut, a bus ride, a lesson.
服务是为你完成的工作—— 理发、乘车、一堂课。
Both use scarce resources, so both force a choice.
两者都消耗稀缺资源，所以都迫使你做出选择。
When wants outrun resources, every good and every service is scarce.
当欲望超过资源时，每一种物品和每一种服务都是稀缺的。
That is why economics never runs out of questions.
这就是经济学永远有问题可问的原因。
If you cannot have everything, you must choose — and every choice costs something.
既然不能什么都要，你就必须选择——而每个选择都要付出代价。
Opportunity cost is the next best alternative you give up.
机会成本是你放弃的次优选择。
The next best one, not all the others.
是次优的那一个，不是其余全部。
A consumer buys a phone and gives up the holiday.
消费者买了手机，就放弃了那次旅行。
A firm uses its factory for cars and gives up the trucks.
企业用工厂造汽车，就放弃了卡车。
A government spends on hospitals and gives up the schools.
政府把钱花在医院上，就放弃了学校。
Opportunity cost is not a special exam phrase.
机会成本不是考试专用的说法。
It hits everyone who chooses.
每个做选择的人都会遇到它。
Consumers spend limited income: money on a phone is money not spent on a holiday.
消费者的收入有限：钱花在手机上，就不能再花在旅行上。
Producers and firms have limited capacity: a factory line making cars cannot make trucks at the same time.
生产者和企业的产能有限：同一条生产线在造汽车时，就不能同时造卡车。
Governments spend limited tax revenue: hospitals now means fewer new schools.
政府的税收有限：现在建医院，就意味着少建新学校。
In every case the cost is the next best option left behind — the one you almost chose.
每一种情况里，代价都是被留下的次优选项——你差点选中的那一个。
Economists separate two kinds of statement.
经济学家把表述分成两类。
A positive statement is about fact: it can be tested, and shown true or false.
实证表述讲的是事实：它可以被检验，能判断真假。
A higher petrol price reduces the amount bought — that is positive.
汽油价格上升会减少购买量——这就是实证表述。
A normative statement is about opinion.
规范表述讲的是观点。
It contains the word should, and cannot be tested.
它含有"应该"，无法被检验。
The government should make petrol cheaper — that is normative.
政府应该让汽油更便宜——这就是规范表述。
It rests on a value judgement.
它建立在价值判断之上。
Here is the same split drawn as two cards.
这里用两张卡片画出同样的区分。
On the left, a positive claim: raise the petrol price and people buy less.
左边是实证主张：提高汽油价格，人们就买得更少。
You can check the data and call it true or false.
你可以查数据，判定它真或假。
On the right, a normative claim: the government should cut the price.
右边是规范主张：政府应该降价。
No data set can prove that.
没有哪组数据能证明这一点。
Two people can share every fact and still disagree, because each holds a different value judgement about what is fair.
两个人可以共享全部事实，却仍然意见不合， 因为他们对什么算公平持有不同的价值判断。
In the exam, hunt for the word should — it almost always marks opinion.
考试时，去找"应该"这个词——它几乎总是观点的标记。
Economics is a social science: it studies how people behave when they choose.
经济学是一门社会科学：它研究人在做选择时的行为。
It builds simple models of the real world and tests them with data.
它建立现实世界的简单模型，再用数据检验。
The world moves in every direction at once, so economists change one thing and hold everything else still.
世界同时在各个方向变化， 所以经济学家只改变一个因素，其余全部保持不变。
The Latin name for that is ceteris paribus.
这个做法的拉丁名字叫 ceteris paribus，也就是其他条件不变。
Microeconomics studies single parts: one market, one firm, one consumer.
微观经济学研究局部：一个市场、一家企业、一位消费者。
Macroeconomics studies the whole economy: output, jobs and prices.
宏观经济学研究整个经济：产出、就业和物价。
Take a simple model claim: if the price of coffee rises, people buy less coffee, ceteris paribus.
来看一个简单的模型说法：如果咖啡价格上升，人们就少买咖啡，其他条件不变。
That Latin tag means we hold incomes, tastes and other prices fixed while we watch one change.
这个拉丁标签的意思是：在我们观察这一个变化时，把收入、偏好和其他价格都固定住。
In the real world those other things move too — but the model isolates one cause.
现实世界里其他东西也会动——但模型把一个原因单独拿出来。
Microeconomics uses this tool on one market at a time.
微观经济学用这个工具一次只看一个市场。
Macroeconomics asks bigger questions: total output, total jobs, the general price level.
宏观经济学问更大的问题： 总产出、总就业、一般物价水平。
Same method, different scale.
方法相同，尺度不同。
So what do we produce with?
那么我们用什么来生产？
Four factors, and each earns its own reward.
四种要素，每一种都赚得自己的报酬。
Land is the natural resources — fields, water, oil, minerals — and its reward is rent.
土地是自然资源——田地、水、石油、矿产——它的报酬是地租。
Labour is human work, and its reward is wages.
劳动是人的工作，它的报酬是工资。
Capital is the man-made things we produce with: machines, tools, factories. Its reward is interest.
资本是我们用来生产的人造之物： 机器、工具、工厂，它的报酬是利息。
And enterprise is the skill of bringing the other three together and taking the risk. Its reward is profit.
而企业家才能是把前三者组织起来并承担风险的能力，它的报酬是利润。
Keep this table in your head for the exam.
考试时把这张表记在脑子里。
Land earns rent.
土地赚得地租。
Labour earns wages — and labour is both physical and mental work.
劳动赚得工资—— 劳动既包括体力工作也包括脑力工作。
Capital earns interest: the return on machines, tools and factories that help us produce.
资本赚得利息： 那是机器、工具和工厂帮助我们生产所带来的回报。
Enterprise earns profit.
企业家才能赚得利润。
Enterprise is supplied by the entrepreneur — the person with the business idea who risks their own money.
企业家才能由企业家提供——那个有商业想法、用自己的钱承担风险的人。
Mix up a factor with the wrong reward and the mark is gone.
把要素和错误的报酬配在一起，分就丢了。
Look at an open-pit mine.
看一看露天矿。
That is land in the economist's sense: not just fields, but minerals, oil, water and the ground itself.
这就是经济学家所说的土地：不只是田地， 还有矿产、石油、水和地面本身。
Some of these are non-renewable resources — oil and coal can run out.
其中有些是不可再生资源—— 石油和煤炭会用完。
Once extracted and burned, they are gone.
一旦被开采并烧掉，它们就没了。
So using them today has a clear opportunity cost for future generations.
所以今天使用它们，对未来世代有明确的机会成本。
Land still earns rent, but scarcity of non-renewables makes that rent a permanent policy question, not a side note.
土地仍然赚得地租，但不可再生资源的稀缺，让地租成为长期的政策问题， 而不是旁注。
Specialisation means a worker, a firm or a country makes only what it is best at, and trades for the rest.
专业化是指一个工人、一家企业或一个国家只生产自己最擅长的东西，其余通过交换获得。
Inside a workplace this becomes the division of labour: one big job split into small tasks, each worker repeating one.
在工作场所内部，这就成了劳动分工：一件大工作被拆成小任务，每个工人重复做一项。
The gains are real: workers get faster, no time is lost switching, so output rises and costs fall.
好处是实实在在的：工人做得更快，也不浪费时间转换，于是产出上升、成本下降。
But there is a cost.
但也有代价。
The work is boring, so people leave.
工作枯燥，于是有人辞职。
One absence can stop the line.
一个人缺勤就可能让整条线停下来。
And each worker learns only one narrow skill.
而且每个工人只学会一项狭窄的技能。
A car assembly line shows both capital and the division of labour.
一条汽车装配线同时展示了资本和劳动分工。
Machines and robots are capital: man-made tools that raise output.
机器和机器人是资本： 提高产出的人造工具。
Each worker repeats one small task, so practice makes them faster and less time is lost moving between jobs.
每个工人重复一项小任务，练习让他们更快， 在岗位之间移动的时间浪费也更少。
Output per worker rises and unit costs fall.
人均产出上升，单位成本下降。
The risks sit in the same picture: boredom, high turnover, and a stoppage if one station fails.
风险也在同一画面里：枯燥、高离职率，以及一个工位停摆就会整线中断。
Specialisation raises efficiency — and interdependence.
专业化提高效率——也提高相互依赖。
A factor can only move to a new use if it is mobile.
一种要素只有具备流动性，才能转到新的用途。
Occupational mobility is how easily it changes job or use — a teacher who retrains as a nurse.
职业流动性是指它改变工作或用途的难易——比如教师重新培训成为护士。
Geographical mobility is how easily it moves to a new place; land cannot move at all.
地理流动性是指它迁到新地方的难易；土地根本无法移动。
Labour is often less mobile than it looks — family ties, housing costs and missing skills hold workers in place.
劳动的流动性往往比看上去要低——家庭牵绊、房价和缺少技能都把工人留在原地。
Why is labour often stuck?
为什么劳动常常被卡住？
Family ties keep people near relatives and schools.
家庭牵绊把人留在亲属和学校附近。
Housing costs make a move to a high-wage city unaffordable.
房价让迁往高工资城市变得负担不起。
Missing skills block occupational switches even when vacancies exist.
缺少技能会挡住职业转换， 即使有空缺岗位也进不去。
Capital can be sold and rebuilt elsewhere, and enterprise can relocate with the founder — but land has zero geographical mobility.
资本可以卖掉并在别处重建， 企业家才能可以随创办人迁移——但土地的地理流动性为零。
When examiners ask about factor mobility, name the barrier, not just the definition.
考官问要素流动性时，要说出障碍，而不只是定义。
So who decides what gets made?
那么谁来决定生产什么？
In a market economy, firms and households own the resources and prices decide.
在市场经济中，企业和家庭拥有资源，由价格来决定。
Choice is wide and prices are low, but the income gap grows.
选择丰富、价格低廉，但收入差距扩大。
In a planned economy the government owns the resources and decides what, how and for whom.
在计划经济中，政府拥有资源， 并决定生产什么、怎样生产、为谁生产。
Incomes are more equal, but incentives are weak and shortages are common.
收入更平均，但激励不足、短缺常见。
Almost every real country is a mixed economy — a private sector and a public sector side by side.
几乎每个真实国家都是混合经济——私营部门与公共部门并存。
Real systems sit on a spectrum.
真实的体制落在一条光谱上。
At one end, a pure market: private owners and free prices.
一端是纯粹市场：私人所有者与自由价格。
At the other, full government planning — also called a command economy.
另一端是全面的政府计划——也叫指令经济。
In between lie mixed economies, where the private sector and the public sector both decide.
中间是混合经济， 私营部门与公共部门都做决策。
China's economy is often described as a socialist market economy: markets set most prices, while the state guides key sectors and owns major enterprises.
中国的经济常被描述为社会主义市场经济： 市场决定大部分价格，而国家引导关键部门并拥有主要企业。
No large country sits at either pure extreme.
没有哪个大国坐在纯极端上。
Compare the three on strengths and weaknesses.
从优点和缺点比较这三种。
Markets give choice, low prices and strong incentives to work and invent — but the gap between rich and poor grows, and some goods are never supplied.
市场带来选择、低价格和努力工作与发明的强激励—— 但贫富差距扩大，有些物品根本没有人供给。
Planned systems narrow that gap and provide key goods for all — but incentives are weak, shortages and surpluses appear, and change is slow.
计划体制缩小差距， 并为所有人提供关键物品——但激励弱，短缺与过剩都会出现，变革缓慢。
Mixed systems try to keep the best of both.
混合体制试图保留两者的优点。
The hard part is finding the right balance.
难的是找到正确的平衡。
In a market nobody is in charge.
在市场中没有人发号施令。
Prices do the work, and they do three jobs at once.
价格在做事，而且同时做三件事。
Signalling: a rising price tells everyone this good is wanted, so resources should move here.
信号传递：价格上升，就告诉所有人这种物品受欢迎，资源应当转过来。
Incentive: a higher price rewards producers, so they supply more.
激励：更高的价格奖励生产者，于是他们供给更多。
Rationing: when a good is scarce, the higher price shares it out among those willing and able to pay.
配给：当物品稀缺时，更高的价格把它分配给那些愿意且有能力支付的人。
Put price in the centre of the diagram.
把价格放在图的中心。
Three arrows leave it.
三条箭头从它出发。
Signalling shows where resources are wanted: a rising price says make more of this.
信号传递显示资源被需要的地方： 价格上升就表示多生产这种东西。
Incentive rewards the producers who respond, so supply expands.
激励奖励那些作出反应的生产者，于是供给扩大。
Rationing shares a scarce good among those willing and able to pay — not by a queue, but by the price itself.
配给把稀缺物品分给那些愿意且有能力支付的人——不是靠排队，而是靠价格本身。
In a market economy these three jobs allocate resources without a central planner.
在市场经济中，这三件事在没有中央计划者的情况下配置资源。
That is the price mechanism at work.
这就是价格机制在起作用。
Here is the picture economists draw for all of this: the production possibility curve.
这就是经济学家为这一切所画的图：生产可能性曲线。
Imagine a country making only two things, food and machines.
设想一个国家只生产两种东西：食物和机器。
The curve shows every largest combination it can produce when all its resources are fully used.
这条曲线表示当全部资源被充分使用时，它能生产的所有最大组合。
Watch it move along the curve: to make more of one good, it must take resources from the other.
看它沿着曲线移动：要多生产一种物品，就必须从另一种上抽走资源。
That trade-off is opportunity cost.
这种取舍就是机会成本。
Formally, a production possibility curve — the PPC — is a line showing the largest combinations of two goods an economy can make when all resources are fully and well used.
正式地说，生产可能性曲线（PPC）是一条线，表示当全部资源被充分且良好使用时， 一个经济体能生产的两种物品的最大组合。
Food on one axis, machines on the other.
一轴是食物，另一轴是机器。
Every point on the curve is a maximum: more of both at once is impossible with today's resources.
曲线上的每一点都是最大值：以今天的资源，两种同时再增加是不可能的。
Moving along the curve is a trade-off — more food means fewer machines.
沿着曲线移动就是取舍——更多食物意味着更少机器。
The slope of the curve is opportunity cost drawn as geometry.
曲线的斜率就是被画成几何的机会成本。
Three positions matter, and the exam asks for all three.
有三个位置很重要，考试三个都会问。
A point on the curve uses every resource fully — that is efficient.
曲线上的点把每一份资源都用满了—— 这是有效率的。
A point inside the curve wastes resources: unemployed workers, idle machines.
曲线内部的点浪费了资源：失业的工人、闲置的机器。
A point outside the curve is impossible today; there are not enough resources.
曲线外部的点今天不可能实现，因为资源不够。
That is scarcity, drawn as a boundary.
这就是被画成一条边界的稀缺性。
The shape matters too: a straight line means constant opportunity cost, and a curve bowed outwards means increasing opportunity cost.
形状也很重要：直线表示机会成本不变，向外凸出的曲线表示机会成本递增。
Read the three labelled points carefully.
仔细读三个标出的点。
On the curve: full efficiency — every worker and machine is used well.
曲线上：充分效率——每个工人和每台机器都被用好了。
Inside: waste.
内部：浪费。
Unemployment of labour is the classic example, but idle capital counts too.
劳动失业是经典例子，闲置资本也算。
The economy could do better without any new resources.
经济体不用新增任何资源就能做得更好。
Outside: unattainable today.
外部：今天不可达到。
Scarcity is the boundary itself.
稀缺性就是这条边界本身。
Examiners love a short phrase: inside means unused resources, on means efficient, outside means impossible for now.
考官喜欢短句：内部表示未使用的资源， 曲线上表示有效率，外部表示目前不可能。
Shape is not decoration.
形状不是装饰。
A straight-line production possibility curve means constant opportunity cost: each extra unit of food costs the same number of machines.
直线生产可能性曲线表示机会成本不变： 每多一单位食物，付出的机器数量相同。
A curve that bows outwards means increasing opportunity cost: each extra unit of food costs more and more machines. Why?
向外凸出的曲线表示机会成本递增： 每多一单位食物，付出的机器越来越多。
Resources are not equally good at making both goods.
为什么？ 资源并非同样擅长生产两种物品。
Start from all food. The first factors you move into cars are the ones least suited to farming, so you give up very little food.
从全部生产食物开始， 你最先调去造车的，是最不适合务农的要素，所以放弃的食物很少。
Keep going, and you must move factors that are increasingly good at farming and increasingly bad at making cars — so each extra car costs more and more food.
继续下去，你不得不调动那些越来越擅长务农、越来越不擅长造车的要素—— 于是每多造一辆车，要付出越来越多的食物。
That is why the curve is concave, bowed outwards.
这就是曲线向外凸出（凹形）的原因。
Specialised factors make the concave shape the usual textbook picture.
专门化的要素，使这个形状成为教材中的常见画面。
Now move the whole curve.
现在让整条曲线移动。
With more resources, or better ones — new technology, a larger or more skilled workforce — the entire curve shifts outward.
有了更多或更好的资源——新技术、更多或更熟练的劳动力—— 整条曲线就向外移动。
That is economic growth: more of both goods becomes possible.
这就是经济增长：两种物品都能生产得更多。
War or disaster pushes it inward, and that is decline.
战争或灾难则把它推向内侧，那就是衰退。
Capital goods are goods used to make other goods, like machines.
资本品是用来生产其他物品的物品，比如机器。
Consumer goods are used directly.
消费品则被人们直接使用。
Build more capital goods now, and the curve shifts out further later.
今天多造资本品，将来曲线就向外移得更远。
An outward shift is economic growth: more of both goods becomes possible.
向外移动是经济增长：两种物品都能生产得更多。
Causes include more resources, better technology, or a larger and more skilled workforce.
原因包括更多资源、更好技术，或更大更熟练的劳动力。
An inward shift is economic decline — war, natural disaster, or a collapse in the capital stock.
向内移动是经济衰退——战争、自然灾害，或资本存量崩溃。
Moving along the old curve is reallocation; shifting the whole curve is a change in capacity.
沿旧曲线移动是再配置；整条曲线移动是产能变化。
Do not mix those two stories in the same sentence.
不要在同一句话里把这两种故事混在一起。
A country also chooses between capital goods and consumer goods today.
一个国家今天还要在资本品和消费品之间选择。
Capital goods — machines and factories — help make other goods later.
资本品——机器和工厂——帮助以后生产其他物品。
Consumer goods — food and clothes — are used right away.
消费品——食物和衣服——马上就被使用。
More capital goods now means fewer consumer goods now.
今天更多资本品，意味着今天更少消费品。
But a larger capital stock helps the economy grow faster, so the future curve shifts out further.
但更大的资本存量帮助经济更快增长，所以未来的曲线向外移得更远。
That is another opportunity cost: present consumption against future capacity.
这又是一种机会成本：现在的消费对未来的产能。
Now the goods themselves.
现在来看物品本身。
A free good has unlimited supply and no opportunity cost, so it has no price — air, sunlight.
免费物品供给无限、没有机会成本，所以没有价格—— 比如空气和阳光。
Everything else is an economic good: scarce, so it has a price.
其余的都是经济物品：稀缺，因而有价格。
A private good has two features.
私人物品有两个特征。
Rivalry: if I eat the apple, you cannot.
竞争性：我把苹果吃了，你就吃不到。
Excludability: pay, or you are kept out.
排他性：不付钱就会被挡在外面。
A public good is the exact opposite — non-rival and non-excludable, like street lighting.
公共物品恰恰相反——非竞争性且非排他性， 比如路灯。
That creates the free-rider problem: people enjoy it without paying, so no firm can profit and the government must provide it.
这就产生了搭便车问题：人们不付钱也能享用， 于是没有企业能获利，只能由政府提供。
A free good has unlimited supply and zero opportunity cost, so it carries no price — air or sunlight in ordinary conditions.
免费物品供给无限、机会成本为零，所以没有价格—— 在通常条件下，空气或阳光就是这样。
An economic good is scarce: making it uses resources that could have made something else, so it has a price.
经济物品是稀缺的： 生产它要占用本可以生产别的东西的资源，所以它有价格。
Most private goods are economic goods with two further features.
大多数私人物品是经济物品，还带有两个进一步特征。
Rivalry means my use cuts yours.
竞争性意味着我的使用会减少你的。
Excludability means the seller can keep out non-payers.
排他性意味着卖家可以挡住不付钱的人。
Free goods are rare; almost everything on a syllabus is economic.
免费物品很少；大纲上几乎一切都是经济物品。
Rivalry and excludability give four boxes, not two.
竞争性和排他性给出四个格子，而不是两个。
Private goods are rival and excludable — the apple.
私人物品既竞争又可排他——苹果。
Club goods are non-rival but excludable — a streaming subscription or a toll road with spare capacity.
俱乐部物品不竞争但可排他——流媒体订阅，或还有余量的收费公路。
Common resources are rival but non-excludable — fish in the open sea.
共有资源竞争但不可排他——公海上的鱼。
Public goods are non-rival and non-excludable — street lighting and national defence.
公共物品既不竞争也不可排他—— 路灯和国防。
The free-rider problem hits the non-excludable boxes hardest, so private firms under-supply them and government steps in.
搭便车问题对不可排他的格子打击最重， 所以私人企业供给不足，政府介入。
Why must the government provide national defence?
为什么必须由政府提供国防？
Defence is non-rival: one more protected person does not shrink protection for others.
国防是非竞争的：多保护一个人， 并不会削弱对其他人的保护。
It is non-excludable: you cannot fence out a non-payer inside the same borders.
它是非排他的：在同一国界内，你无法把不付钱的人挡在外面。
So each person has an incentive to free-ride — enjoy the protection without paying.
于是每个人都有搭便车的动机——享受保护却不付钱。
Private firms cannot collect enough revenue, so they will not supply it.
私人企业收不够钱，所以不会供给它。
Street lighting works the same way.
路灯也是同一逻辑。
Public goods need public provision.
公共物品需要公共提供。
Two more categories, about what people know.
还有两类，它们关乎人们知道多少。
A merit good is better for you than you realise, so you buy too little — education, health care.
优值品对你的好处比你以为的更大， 所以你买得太少——比如教育和医疗。
A demerit good is worse for you than you realise, so you buy too much — cigarettes, alcohol.
劣值品对你的害处比你以为的更大， 所以你买得太多——比如香烟和酒。
The cause is information failure: people do not have the full facts, or do not use them.
原因是信息失灵： 人们没有掌握完整的事实，或者掌握了也不用。
And what belongs on each list is partly a value judgement.
而什么该放进哪一类，部分是价值判断。
Education is the classic merit good.
教育是经典的优值品。
Its full value is easy to underestimate: better jobs for the person, and a more skilled society for everyone else.
它的全部价值很容易被低估： 对个人是更好的工作，对他人是一个技能更高的社会。
Left alone, people buy less education than is good for them or for the country.
放任不管时，人们购买的教育少于对自己和国家有利的水平。
That is why governments provide and subsidise it.
这就是政府提供并补贴教育的原因。
The same logic runs the other way for demerit goods like cigarettes: people under-weight the harm, so they consume too much unless policy steps in.
同样的逻辑反过来用于香烟这类劣值品： 人们低估伤害，所以除非政策介入，他们会消费得太多。
One question examiners love.
一道考官很爱出的题。
Why is a production possibility curve usually drawn bowed outwards, not straight?
为什么生产可能性曲线通常画成向外凸出，而不是一条直线？
Pause here and try it.
先暂停，自己试一试。
Ready?
准备好了吗？
A straight line would mean opportunity cost stays constant.
直线意味着机会成本保持不变。
The curve bows because factors are specialised — not perfectly substitutable.
曲线之所以凸出，是因为生产要素是专门化的——并非完全可替代。
The first factors you move from food into cars are the worst farmers, so little food is lost.
你最先从食物调去造汽车的，是最不擅长务农的那些要素，所以损失的食物很少。
Keep going and you must move better and better farmers, so each car costs more food.
继续下去，就不得不调走越来越擅长务农的要素，于是每辆车要付出更多食物。
That is increasing opportunity cost.
这就是机会成本递增。
A straight-line production possibility curve is not wrong.
直线生产可能性曲线并没有错。
It just assumes factors are perfectly substitutable — equally good at making either good.
它只是假设要素完全可替代—— 同样擅长生产任何一种物品。
Name that assumption and you earn the mark.
说出这个假设，你就拿到分数。
The bowed curve drops the assumption: factors are specialised, so opportunity cost rises as you reallocate.
凸出曲线放弃了这个假设：要素是专门化的，所以再配置时机会成本上升。
Starting from all food, the first resources moved into cars are the least suited to farming.
从全部生产食物出发，最先调去造汽车的资源最不适合务农。
Later moves take better farmers, and each extra car costs more food.
后面的调动带走更好的农民，每多一辆车就要付出更多食物。
Three marks students give away.
三个学生白白丢掉的分。
First, define opportunity cost as the next best alternative given up — not everything given up.
第一，把机会成本定义为放弃的次优选择—— 不是放弃的全部。
Second, read the production possibility curve correctly: inside means waste, on the curve means efficient, outside means impossible.
第二，正确解读生产可能性曲线： 内部表示浪费，曲线上表示有效率，外部表示不可能。
Third, label a statement positive or normative by testing it — if it says what should happen, it is normative.
第三，用检验来判断一句话是实证还是规范—— 如果它说的是"应该"怎样，那就是规范表述。
Get these right, and this topic is yours.
把这些做对，这个专题就是你的了。
One more checklist item.
还有一条检查清单。
Classify goods carefully.
仔细给物品分类。
Free versus economic is about scarcity and opportunity cost.
免费对经济，讲的是稀缺和机会成本。
Private versus public is about rivalry and excludability.
私人对公共，讲的是竞争性和排他性。
Merit and demerit goods are about information failure and value judgements — not the same as public goods.
优值品和劣值品讲的是信息失灵和价值判断—— 它们不等于公共物品。
Frame every answer around scarcity and choice, and name the next best alternative.
每个答案都围绕稀缺与选择展开，并说出次优选择。
That is how this whole topic holds together.
这就是整个专题连在一起的方式。