The Allocation of Resources
IGCSE Economics Topic 2 21:51 English narration · English + 中文 subtitles burned in
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Nobody in the world is in charge of deciding how many coffee beans to grow.
世界上没有任何人负责决定要种多少咖啡豆。
No committee meets. No plan is written.
没有委员会开会，也没有人写计划。
And yet, most mornings, there is coffee.
可是大多数早晨，咖啡都在。
Nobody decided that — the price did.
这不是谁决定的——是价格决定的。
The price is a signal that travels through a market and tells millions of strangers what to make and what to buy.
价格是一个穿过市场的信号，它告诉千百万素不相识的人：该生产什么，该买什么。
This lesson is how that works, and what happens when it does not.
这节课讲的就是它如何运作，以及当它失灵时会发生什么。
Welcome to Topic Two.
欢迎来到第二单元。
First, two words.
先讲两个词。
Microeconomics studies one part of the economy — one industry, one product. Macroeconomics studies the whole economy.
微观经济学研究经济的一个部分——某个行业、某种产品； 宏观经济学研究整个经济。
This topic is micro.
这一单元属于微观。
A market is anywhere buyers and sellers meet to trade. It needs no building; it can be online.
市场是任何买家和卖家相遇进行交易的地方，它不需要建筑，也可以在网上。
In a free market the price mechanism allocates resources — it decides what is made, how, and for whom. Price does three jobs, and the exam names all three.
在自由市场里，价格机制配置资源——它决定生产什么、怎么生产、为谁生产。
Signalling: a change in price tells everyone what is happening. Incentive: a higher price gives firms a reason to produce more. Rationing: when a good is scarce its price rises, and that shares out the limited amount.
价格有三项职能，考试三项都会点名：信号职能，价格变化告诉所有人正在发生什么； 激励职能，更高的价格给企业更多生产的理由；配给职能， 当一种物品稀缺时它的价格上升，从而把有限的数量分配出去。
Here is one market you can see.
这是你能看见的一种市场。
On a stock exchange floor, buyers and sellers trade shares.
在证券交易所的交易大厅里，买家和卖家买卖股票。
Their offers set the price of each share — no single person decides it.
他们的报价决定了每只股票的价格——不是某一个人说了算。
But a market does not need a floor, or a building at all.
但市场不需要交易大厅，甚至不需要建筑。
Online shops, phone orders, and a street stall are all markets.
网店、电话订购、路边摊都是市场。
Anywhere buyers and sellers meet to trade counts.
只要买家和卖家相遇交易，就算市场。
When the market is free, the free movement of prices is what allocates scarce resources.
当市场是自由的， 价格的自由变动就是配置稀缺资源的方式。
Look again at those three jobs, one by one.
再把这三项职能一项一项看清楚。
Signalling: a rising price signals make more, and a falling price signals make less.
信号：价格上升信号着多生产，价格下降信号着少生产。
Buyers and sellers read that signal without anyone writing a plan.
买家和卖家读这个信号，没有人写计划。
Incentive: the higher price is also a reason for firms to produce more, because they can earn more money.
激励：更高的价格也是企业多生产的理由， 因为他们能赚更多钱。
Rationing: when a product is scarce, its price rises.
配给：当产品稀缺时价格上升。
Only those willing to pay the higher price still buy it — so the limited amount is shared out.
只有愿意付更高价的人还在买—— 有限的数量就这样被分配出去。
Three jobs, one number on the vertical axis of every demand and supply diagram.
三项职能，一个写在每一张供需图纵轴上的数字。
Demand is the amount of a good that consumers are willing and able to buy at each price, in a period of time.
需求，是消费者在一段时间内、在每一个价格上愿意并且能够购买的数量。
Willing and able — wanting it is not enough.
愿意并且能够——只是想要还不够。
The law of demand says that when the price rises, the quantity demanded falls, and when the price falls, the quantity demanded rises.
需求定律说：价格上升时需求量下降， 价格下降时需求量上升。
Price and quantity move in opposite directions; we call that an inverse relationship.
价格和数量朝相反方向变动，我们把这叫做反向关系。
That is why the demand curve slopes downward.
这就是需求曲线向下倾斜的原因。
And every demand statement carries two Latin words: ceteris paribus, meaning all other things stay the same.
而每一句关于需求的话都带着两个拉丁词： ceteris paribus，意思是其他条件不变。
Now separate two words that the exam loves to mix up.
现在把考试最爱混在一起的两个词分开。
Quantity demanded is the amount bought at one price — one point on the curve.
需求量是在某一个价格上买到的数量——曲线上的一个点。
Demand is the whole pattern of buying at every price — the whole line.
需求是在每一个价格上的整套购买模式——整条线。
On the diagram, price sits on the up axis and quantity on the across axis.
在图上，价格在纵轴，数量在横轴。
The demand curve slopes down from left to right: high price, low quantity; low price, high quantity.
需求曲线从左上向右下倾斜：高价低量，低价高量。
Change the good's own price and you slide along the same line.
物品自身价格变了，你沿着同一条线滑动。
Change income, tastes, population, or related prices, and the whole curve shifts right for more demand, or left for less.
收入、偏好、人口或相关价格变了，整条曲线右移表示需求更多，左移表示更少。
Own price never shifts the curve.
自身价格绝不会让曲线移动。
Now the single most examined distinction in this topic.
现在是这一单元最常考的一个区分。
A change in the good's own price is a movement along the curve — you slide to a new point on the same line.
物品自身价格的变化，是沿着曲线移动—— 你滑到同一条线上的一个新点。
A change in anything else shifts the whole curve. Rightward means more is demanded at every price; leftward means less.
其他任何东西的变化，都会让整条曲线移动： 向右意味着在每一个价格上需求都更多，向左意味着更少。
The conditions of demand are what shift it.
让曲线移动的，是需求的条件。
Income: more income, more demand.
收入：收入更高，需求更多。
Tastes: if a good becomes popular demand rises.
偏好：某样东西流行了，需求上升。
Substitutes, goods used instead of each other — if coffee gets dearer, demand for tea rises.
替代品，即互相代替使用的物品——咖啡贵了，茶的需求就上升。
Complements, goods used together — if cars get dearer, demand for fuel falls.
互补品，即一起使用的物品——汽车贵了，燃油的需求就下降。
Population, and advertising.
还有人口和广告。
Six things to learn, and none of them is the good's own price.
六样要记住的东西，而它们没有一样是这个物品自身的价格。
Supply is the amount firms are willing and able to sell at each price.
供给，是企业在每一个价格上愿意并且能够出售的数量。
The law of supply says that when the price rises, the quantity supplied rises too.
供给定律说：价格上升时，供给量也上升。
Price and quantity move the same way — a direct relationship — because a high price means a firm can earn more.
价格和数量朝同一方向变动——这是正向关系—— 因为高价意味着企业能赚得更多。
So the supply curve slopes upward.
所以供给曲线向上倾斜。
The same rule about movement and shift applies, and here are the conditions of supply.
关于"沿曲线移动"和"曲线移动"的规则同样适用，下面是供给的条件。
Costs of production: if costs rise, supply falls.
生产成本：成本上升，供给下降。
Technology: better technology lowers costs, so supply rises.
技术：更好的技术降低成本，所以供给上升。
A tax raises costs, so supply falls; a subsidy, which is money from the government, lowers costs, so supply rises.
税收提高成本，供给下降；补贴，也就是政府给的钱，降低成本，供给上升。
Then weather, which matters for farm goods, and the number of firms.
再加上天气——对农产品很重要——以及企业的数量。
Same careful language on the supply side.
供给这边也要用同样仔细的语言。
Quantity supplied is the amount offered at one price — one point.
供给量是在某一个价格上提供的数量——一个点。
Supply is the whole pattern at every price — the whole upward-sloping curve.
供给是在每一个价格上的整套模式——整条向上倾斜的曲线。
Own price moves you along the curve.
自身价格让你沿曲线移动。
Anything else shifts it.
其他任何变化让曲线移动。
Lower costs, better technology, a subsidy, better weather for farms, or more firms, all shift supply right — more is offered at every price.
更低成本、更好技术、补贴、对农业更好的天气，或更多企业， 都会使供给右移——每一个价格上提供的都更多。
Higher costs or a tax shift it left.
更高成本或税收则使它左移。
Always ask: did the good's own price change, or did a condition of supply change?
永远先问：是物品自身价格变了，还是某个供给条件变了？
Watch supply shift right on the animation.
看动画里供给向右移动。
The upward curve moves out.
向上的曲线外移。
The crossing with demand falls and slides right.
它与需求的交点下移并向右滑。
So the equilibrium price falls, and the equilibrium quantity rises.
于是均衡价格下降，均衡数量上升。
That is the pattern every time supply increases: more is traded, but each unit sells for less.
供给增加时每一次都是这个模式： 成交更多，但每一单位卖得更便宜。
If supply had shifted left instead, price would rise and quantity would fall.
如果供给向左移，价格会上升、数量会下降。
Learn that pair cold.
把这一对结果记牢。
Put both curves on one diagram.
把两条曲线画在同一张图上。
They cross at one point, and that point sets the price.
它们交于一点，而这一点决定了价格。
The equilibrium price is the price at which the amount buyers want to buy exactly equals the amount firms want to sell. The equilibrium quantity is the amount traded there.
均衡价格，是买家想买的数量恰好等于企业想卖的数量时的那个价格； 均衡数量，就是在那里成交的数量。
At equilibrium, quantity demanded equals quantity supplied. Nothing is left over on the shelf, and no buyer is left waiting.
在均衡处，需求量等于供给量： 货架上没有剩下的东西，也没有买家在等待。
Get into the habit of labelling both: the price on the up axis, the quantity on the across axis, with dashed lines to each.
养成把两者都标出来的习惯： 价格在纵轴，数量在横轴，并用虚线连到各自的轴上。
Here is the exam diagram.
这就是考试图。
Demand slopes down, supply slopes up, and they cross once.
需求向下倾斜，供给向上倾斜，它们交于一点。
From the cross, drop a dashed line to the quantity axis and mark the equilibrium quantity. From the cross, run a dashed line to the price axis and mark the equilibrium price.
从交点向数量轴画虚线，标出均衡数量；从交点向价格轴画虚线，标出均衡价格。
Without those two labels, the drawing has already lost marks.
没有这两个标注，画图已经丢分。
At that point alone, quantity demanded equals quantity supplied.
只有在那一点，需求量等于供给量。
Anywhere else on the price axis, the market is out of balance.
在价格轴上的任何其他位置，市场都不平衡。
When a curve shifts, the crossing point moves — so price and quantity change.
当一条曲线移动时，交点也移动，于是价格和数量都改变。
Four results, and you should know all four cold.
一共四种结果，四种都要记牢。
If demand rises, price rises and quantity rises. If demand falls, price falls and quantity falls.
需求上升，价格上升、数量上升；需求下降，价格下降、数量下降——需求让两者同向。
Demand moves them together. If supply rises, price falls and quantity rises. If supply falls, price rises and quantity falls.
供给上升，价格下降、数量上升；供给下降，价格上升、数量下降—— 供给让两者反向。
Supply is the one that pushes them in opposite directions — that is the pattern to remember, and it is the half students get wrong.
这就是要记住的规律，也是学生最常搞错的那一半。
Now watch demand shift right.
现在看需求向右移动。
The downward curve moves out.
向下的曲线外移。
The crossing with supply rises and slides right.
它与供给的交点上移并向右滑。
Price rises and quantity rises together — demand moves them the same way.
价格上升，数量也上升——需求让两者同向。
That is why a fashion boom or a rise in income that lifts demand also lifts the market price.
所以时尚热潮或收入上升推高需求时， 市场价格也会被推高。
If demand later fell, both price and quantity would fall.
如果需求随后下降，价格和数量都会下降。
Four shift results, two animations — learn them as pairs.
四种移动结果、两段动画——把它们成对记住。
What if the price is not at equilibrium?
如果价格不在均衡处会怎样？
Then the market is in disequilibrium, and there are exactly two cases.
那市场就处于非均衡状态，而且只有两种情况。
If the price is above equilibrium, firms supply more than buyers want. That is excess supply, also called a surplus, and sellers cut the price.
价格在均衡之上时，企业供给的比买家想要的多，这是超额供给，也叫过剩， 于是卖家降价。
If the price is below equilibrium, buyers want more than firms supply. That is excess demand, also called a shortage, and buyers compete so the price is pushed up.
价格在均衡之下时，买家想要的比企业供给的多，这是超额需求，也叫短缺， 于是买家竞争，价格被推高。
Either way the price is pushed back to equilibrium on its own.
无论哪一种，价格都会自己回到均衡。
Nobody orders it to happen.
没有人下命令让它发生。
Read the figure carefully.
仔细读这张图。
Above the equilibrium price, the supply curve is to the right of the demand curve — quantity supplied is larger than quantity demanded.
在均衡价格之上，供给曲线在需求曲线右边——供给量大于需求量。
That gap is excess supply, a surplus.
这段缺口就是超额供给，也就是过剩。
Sellers cut price to clear stock.
卖家降价清库存。
Below the equilibrium price, demand sits to the right of supply — quantity demanded is larger than quantity supplied.
在均衡价格之下， 需求在供给右边——需求量大于供给量。
That gap is excess demand, a shortage.
这段缺口就是超额需求，也就是短缺。
Buyers bid the price up.
买家把价格抬高。
In both cases the free market pushes price back toward equilibrium without a planner.
两种情况下，自由市场都把价格推回均衡，不需要计划者。
Price elasticity of demand measures how much the quantity demanded changes when the price changes.
需求价格弹性衡量的是：价格变化时，需求量变化了多少。
It is the percentage change in quantity demanded divided by the percentage change in price.
它等于需求量变化的百分比除以价格变化的百分比。
We ignore the minus sign and read the size of the number.
我们忽略负号，只看这个数的大小。
Take an example. A price rises by twenty per cent and the quantity demanded falls by ten per cent.
举个例子：价格上升百分之二十，需求量下降百分之十。
Ten divided by twenty is nought point five.
十除以二十等于零点五。
Now read the number.
现在来读这个数字。
Above one, demand is elastic: quantity changes a lot — think of one brand of crisps, with many substitutes.
大于一，需求富有弹性：数量变化很大——想想某个牌子的薯片，替代品很多。
Below one, demand is inelastic: quantity barely moves — think of petrol or salt.
小于一，需求缺乏弹性：数量几乎不动——想想汽油或者盐。
Exactly one is unit elastic.
正好等于一，是单位弹性。
So nought point five is inelastic.
所以零点五属于缺乏弹性。
What decides whether demand is elastic or inelastic?
是什么决定需求富有弹性还是缺乏弹性？
Three main determinants.
三个主要决定因素。
First, close substitutes: many substitutes means elastic demand, because buyers can switch.
第一，相近替代品：替代品多，需求就富有弹性，因为买家可以换。
One brand of crisps is elastic; salt is not.
某个牌子的薯片富有弹性，盐则不是。
Second, need or luxury: a need with few substitutes is inelastic; a luxury is more elastic.
第二，必需还是奢侈：替代品少的必需品缺乏弹性；奢侈品更富有弹性。
Third, the share of income the good takes: a tiny share of income barely changes buying when price rises, so demand stays inelastic.
第三，该物品占收入的比重：占收入很小的一份，价格上升时购买几乎不变，所以需求保持缺乏弹性。
On the diagram, inelastic demand is the steeper curve — a price change barely moves quantity. Elastic demand is the shallower curve — the same price change moves quantity a lot.
在图上，缺乏弹性的需求是更陡的曲线——价格变化几乎不移动数量； 富有弹性的需求是更平缓的曲线——同样的价格变化会大幅移动数量。
Now why a firm cares.
再说企业为什么在意这个。
Total revenue is price times quantity sold.
总收益等于价格乘以销售数量。
A bus company sells one thousand tickets a day at two pounds each.
一家公交公司每天以每张两英镑卖出一千张票。
It raises the price by ten per cent, to two pounds twenty, and daily sales fall by five per cent, to nine hundred and fifty.
它把价格提高百分之十，到两英镑二十便士， 每天的销量下降百分之五，到九百五十张。
Elasticity is five divided by ten, which is nought point five — inelastic.
弹性是五除以十，等于零点五，缺乏弹性。
Old revenue was two thousand pounds. New revenue is two thousand and ninety. Revenue went up.
原来的总收益是两千英镑，新的总收益是两千零九十英镑，收益上升了。
And here is the rule behind it. If demand is inelastic, raising the price raises revenue, because quantity falls only a little. If demand is elastic, raising the price lowers revenue.
背后的规则是这样的：需求缺乏弹性时，提价会提高总收益，因为数量只下降一点点； 需求富有弹性时，提价会降低总收益。
This is also why a government taxes inelastic goods like cigarettes — people keep buying them, so the tax raises a lot of money.
这也是政府对香烟这类缺乏弹性的物品征税的原因—— 人们照买不误，所以这个税能收到很多钱。
On the diagram, total revenue is the rectangle under the price, out to the quantity sold.
在图上，总收益是价格下方、延伸到销售数量的那个矩形。
To the buyer, that same money is total expenditure — price times quantity spent.
对买家来说，同一笔钱是总支出—— 价格乘以花费的数量。
Watch what a price rise does to the rectangle.
看提价对这个矩形做什么。
When demand is inelastic, the tall thin gain on the price side is bigger than the short loss on the quantity side, so the rectangle grows and revenue rises.
需求缺乏弹性时，价格一侧高而窄的增益 大于数量一侧短的损失，矩形变大，收益上升。
When demand is elastic, the quantity loss dominates, the rectangle shrinks, and revenue falls.
需求富有弹性时，数量损失占主导， 矩形缩小，收益下降。
Firms set prices knowing which case they are in.
企业在知道自己属于哪种情况后才定价格。
Price elasticity of supply is the same idea on the other side: the percentage change in quantity supplied divided by the percentage change in price.
供给价格弹性是同一个想法的另一面：供给量变化的百分比除以价格变化的百分比。
If a price rises by ten per cent and the quantity supplied rises by thirty per cent, the answer is three — above one, so supply is elastic.
如果价格上升百分之十，供给量上升百分之三十，答案是三——大于一，所以供给富有弹性。
What decides it?
是什么决定它呢？
Time: supply is more elastic over a long period, because firms can change how much they make.
时间：时间越长供给越有弹性，因为企业可以改变产量。
Spare capacity: unused machines and workers mean output can rise quickly.
闲置产能：闲置的机器和工人意味着产量可以很快提高。
Stocks: goods already in store can be sold at once.
库存：已经存在仓库里的货可以马上卖出。
And how easily a firm can switch its factors to this good.
还有企业把生产要素转到这种物品上的难易程度。
That is why farm goods have inelastic supply in the short run — a crop takes a season to grow.
这就是为什么农产品在短期内供给缺乏弹性——一季作物要长一个季节。
Two supply curves, same price rise.
两条供给曲线，同样的价格上升。
On the steeper inelastic supply, quantity barely rises.
在更陡的缺乏弹性供给上，数量几乎不上升。
On the shallower elastic supply, quantity rises a lot.
在更平缓的富有弹性供给上，数量上升很多。
Supply is elastic when the price elasticity of supply is greater than one, and inelastic when it is less than one.
供给价格弹性大于一时供给富有弹性， 小于一时缺乏弹性。
A factory with idle machines and finished goods in stock can expand quickly — elastic.
有闲置机器和库存成品的工厂可以迅速扩张——富有弹性。
A farm waiting for a harvest cannot — inelastic in the short run.
等待收成的农场做不到——短期内缺乏弹性。
Time is often the decisive determinant.
时间往往是决定性因素。
Step back from the diagrams.
从图形里退一步。
In a market economy the price mechanism makes all the choices.
在市场经济中，价格机制做出全部选择。
There is no government planning of what to produce.
没有政府规划生产什么。
In a planned economy the opposite is true: the government makes the choices.
在计划经济中正好相反：由政府做选择。
Advantages of the market system: prices guide resources to where they are wanted, without anyone planning; firms compete, so they cut costs and create better goods; and consumers have wide choice.
市场制度的优点：价格把资源引导到需要的地方， 不需要任何人计划；企业互相竞争，于是降低成本、创造更好的产品；消费者有广泛选择。
Disadvantages: some useful goods are not made because they earn no profit; the strong do well while the weak may be left with nothing; and markets can fail.
缺点：有些有用的物品因为赚不到利润而不被生产；强者过得好，弱者可能一无所有； 而且市场会失灵。
That is why almost every real economy is mixed.
这就是为什么几乎每个真实经济体都是混合的。
So the price mechanism is powerful. But sometimes it uses resources badly, and that is market failure.
所以价格机制很强大，但有时它会把资源用得很糟，这就是市场失灵。
The first cause is external costs and benefits.
第一个原因是外部成本和外部效益。
A private cost is the cost to the person doing the activity. An external cost is a cost paid by other people — smoke from a factory harms nearby families.
私人成本，是从事这项活动的人自己承担的成本； 外部成本，是别人替他承担的成本——工厂的烟雾伤害附近的家庭。
Add them together and you get the social cost, the cost to the whole of society.
两者相加，就得到社会成本，也就是整个社会承担的成本。
It works the same way for benefits: private plus external gives social benefit.
效益也是同样的道理： 私人效益加上外部效益，等于社会效益。
And there is the reason markets fail. Firms and consumers only count their own private costs and benefits. Nobody counts the external ones.
市场失灵的原因就在这里： 企业和消费者只计算自己的私人成本和效益，没有人去计算那些外部的部分。
Picture a coal power station sending a plume into the sky.
想象一座燃煤电厂把烟羽送上天空。
The firm pays for coal, labour, and machines — those are private costs.
企业为煤、劳动力和机器付钱——这些是私人成本。
Nearby families breathe dirty air and face higher health costs — that is an external cost, paid by third parties, not by the producer.
附近家庭吸入脏空气，承担更高的健康费用——那是外部成本，由第三方而不是生产者支付。
Social cost is private cost plus external cost, so it is larger than what the firm counts.
社会成本等于私人成本加外部成本，所以比企业所算的更大。
Because the firm ignores the plume, it produces more than is best for society.
因为企业无视烟羽， 它生产得比对社会最优的还多。
That is an inefficient use of resources — market failure in plain sight.
这就是资源的低效率使用——一目了然的市场失灵。
The diagram puts the words on one line: private cost plus external cost equals social cost.
这张图把词语写在一行上：私人成本加外部成本等于社会成本。
Benefits work the same way.
效益也是同样的道理。
A private benefit is the gain to the person doing the activity.
私人效益是从事活动的人自己得到的好处。
An external benefit is a gain others get for free — for example, your neighbour's tidy garden is nice for you too.
外部效益是别人免费得到的好处—— 比如邻居整洁的花园对你也是一种享受。
Private benefit plus external benefit equals social benefit.
私人效益加外部效益等于社会效益。
Markets fail when decision-makers ignore external costs or external benefits, so too much or too little of the activity takes place for society as a whole.
当决策者忽视外部成本或外部效益时，市场就会失灵， 从而对社会整体而言这项活动进行得太多或太少。
Three more failures, from three kinds of good.
还有三种失灵，来自三类物品。
Merit goods are better for you than you realise, so the market makes too few — education and healthcare.
有益物品对你的好处比你意识到的更大， 所以市场生产得太少——教育和医疗就是。
Demerit goods are worse for you than you realise, so the market makes too many — cigarettes and alcohol.
有害物品对你的害处比你意识到的更大， 所以市场生产得太多——香烟和酒精就是。
Public goods are things everyone can use and nobody can be shut out of, like street lights or national defence. The market makes none of them at all, because a firm cannot charge for them.
公共物品是人人都能用、 谁也不能被排除在外的东西，比如路灯或者国防；市场根本一个都不会生产， 因为企业没法为它们收费。
And the last failure is a monopoly: one firm controlling a market.
最后一种失灵是垄断：一家企业控制了一个市场。
With no competition it can charge a high price and let quality slip.
没有竞争，它就可以定高价，还让质量下滑。
A private good is rival and excludable.
私人物品是竞争的、可排他的。
Rival means one person's use leaves less for others.
竞争意味着一个人用了，别人就少了。
Excludable means a firm can stop non-payers from using it.
可排他意味着企业可以阻止不付钱的人使用。
Firms supply private goods gladly, because they can charge.
企业乐意供给私人物品，因为可以收费。
A public good is non-rival and non-excludable.
公共物品是非竞争的、不可排他的。
One more street light does not stop your neighbour enjoying the same light, and you cannot bill passers-by for it.
多一盏路灯不会妨碍邻居享受同一道光， 你也不能向路人收费。
So the market supplies none, and the government must.
所以市场一个都不供给，必须由政府供给。
That free-rider problem is why defence and street lights sit in the public sector.
这种搭便车问题，就是国防和路灯落在公共部门的原因。
Merit and demerit goods fail because of information failure.
有益物品和有害物品失灵，是因为信息失灵。
People mis-judge the true benefit or the true harm.
人们误判了真实的好处或真实的害处。
Education and healthcare are merit goods: the full social benefit is larger than buyers see, so the market under-provides them.
教育和医疗是有益物品：完整的社会效益比买家看到的更大，所以市场供给不足。
Cigarettes and alcohol are demerit goods: the full social cost is larger than users see, so the market over-provides them.
香烟和酒精是有害物品：完整的社会成本比使用者看到的更大，所以市场供给过多。
Governments often subsidise merit goods, tax demerit goods, or regulate both.
政府常常补贴有益物品、对有害物品征税，或对两者加以监管。
The diagram's message is simple: mis-judged goods mean the free market quantity is wrong for society.
图的信息很简单：被误判的物品意味着自由市场的数量对社会来说是错的。
That is why almost every real economy is mixed.
这就是为什么几乎每个真实的经济体都是混合经济。
A mixed economy has a private sector, owned by people and guided by the price mechanism, and a public sector, run by the government.
混合经济有私营部门—— 由个人拥有、由价格机制引导，也有公共部门——由政府运作。
The government steps in to correct market failure. Six methods to learn.
政府介入是为了纠正市场失灵，有六种方法要记。
A maximum price, set below equilibrium to keep something like rent cheap — but it causes a shortage.
最高价格， 定在均衡之下，让房租之类的东西保持便宜——但它会造成短缺。
A minimum price, set above equilibrium to hold a price up — but it causes a surplus.
最低价格，定在均衡之上，把价格托住——但它会造成过剩。
An indirect tax, to cut demand for demerit goods.
间接税，用来减少对有害物品的需求。
A subsidy, to raise output of merit goods.
补贴，用来提高有益物品的产量。
Regulation: rules and laws.
监管，也就是规则和法律。
And direct provision, where the government supplies the good itself.
以及直接提供，由政府自己供应这种物品。
Then one habit for the top marks: always weigh the good effects against the bad.
最后是拿高分的一个习惯： 永远要权衡好处和坏处。
Intervention costs money, and governments get things wrong too.
干预是要花钱的，而且政府也会出错。
Two controls, two opposite mistakes if you draw them wrong.
两种管制，画错了就是两种相反的错误。
A maximum price — also called a price ceiling — is set below equilibrium.
最高价格——也叫价格上限——定在均衡之下。
Quantity demanded then exceeds quantity supplied, so a shortage appears.
于是需求量超过供给量，出现短缺。
That is how a rent ceiling can leave empty waiting lists.
这就是租金上限可能留下一长串等待名单的原因。
A minimum price — a price floor — is set above equilibrium.
最低价格——价格下限——定在均衡之上。
Quantity supplied then exceeds quantity demanded, so a surplus appears.
于是供给量超过需求量，出现过剩。
That is how a high minimum wage can leave some workers without a job.
这就是高最低工资可能让一些工人找不到工作的原因。
Always mark the legal price relative to the free-market equilibrium first.
永远先标出法定价格相对于自由市场均衡的位置。
Watch the ceiling bite.
看价格上限起作用。
The legal maximum sits below the free-market price.
法定最高价落在自由市场价格之下。
Along the demand curve, buyers want more at that low price.
沿着需求曲线，买家在那个低价上想买更多。
Along the supply curve, firms offer less.
沿着供给曲线，企业提供更少。
The horizontal gap between those two quantities is the shortage.
这两个数量之间的水平缺口就是短缺。
The good intention was to keep the product cheap.
好心是想让产品保持便宜。
The side effect is that some willing buyers cannot find it at all.
副作用是一些愿意买的人根本买不到。
Every maximum-price essay needs both the good aim and that shortage cost.
每一篇关于最高价格的作文 都既要写好意，也要写短缺成本。
Intervention can fix market failure, but it is never free.
干预可以纠正市场失灵，但绝不是免费的。
Taxes and rules cost money to collect and to check.
税收和规则要花钱去征收和检查。
Price controls create shortages or surpluses.
价格管制造成短缺或过剩。
Subsidies must be paid for by someone else's taxes.
补贴必须由别人的税来支付。
And governments can get the diagnosis wrong — that is called government failure.
政府也可能诊断错误——这叫做政府失灵。
So for top marks, never end with "the government should intervene" alone.
所以要拿高分，绝不能只写“政府应当干预”就结束。
Always weigh the good effects against the bad ones, and say whether the cure might be worse than the disease.
永远要权衡好的效果和坏的效果，并说明药是否可能比病更糟。
China's economy, for example, is a socialist market economy: market and state side by side, each with strengths and costs.
例如中国的经济是社会主义市场经济：市场与国家并存，各自都有优势和代价。
Three marks students throw away.
三个学生常丢的分。
First, before you draw anything, ask: has the good's own price changed, or something else?
第一，动笔画图之前先问：是这个物品自身的价格变了，还是别的东西变了？
Own price is a movement along the curve. Anything else is a shift.
自身价格是沿着曲线移动，别的东西都是整条曲线移动。
Second, with elasticity, one is the line that matters. Below one is inelastic, so raising the price raises revenue. Above one is elastic, so raising the price lowers revenue.
第二，讲弹性时，一是那条分界线：小于一是缺乏弹性，所以提价会提高总收益； 大于一是富有弹性，所以提价会降低总收益。
Third, label every diagram — both axes, both curves, and the equilibrium price and quantity.
第三，每一张图都要标注——两条轴、两条曲线，还有均衡价格和均衡数量。
Unlabelled diagrams lose marks that the drawing had already earned.
没有标注的图，会把你画图本来已经拿到的分丢掉。