曼昆经济学原理第四章

2

SUPPLYANDDEMANDI:HOWMARKETSWORK供给与需求（I）：市场如何运行TheMarketForcesofSupplyandDemand

供给与需求的市场力量Chapter4TheMarketForcesofSupplyandDemandSupply

and

demand

arethetwowordsthateconomistsusemostoften.Supply

and

demand

aretheforcesthatmakemarketeconomieswork.Modernmicroeconomicsisaboutsupply,demand,andmarketequilibrium.供给与需求的市场力量供给和需求是经济学家最常用的两个词。供给和需求是让市场经济运行的力量。现代微观经济学就是关于供给、需求和市场均衡的学科。Markets

Amarketisagroupofbuyersandsellersofaparticulargoodorservice.Thetermssupplyanddemandrefertothebehaviorofpeople...astheyinteractwithoneanotherinmarkets.市场

市场是指某种物品或劳务的一群买者与卖者的集合。

供给与需求这两个术语是指人们在市场上相互交易时的行为。Marketsandcompetition

市场与竞争

Buyers

determine

demand.买者决定需求

Sellers

determine

supply.卖者决定供给ACompetitiveMarket竞争市场Acompetitivemarketisamarketinwhichtherearemanybuyersandsellerssothateachhasanegligibleimpactonthemarketprice

竞争市场——有很多买者和卖者的市场，所以每一个买者或卖者对市场价格的影响都可以忽略不计。Competition:PerfectandOtherwiseProductsarethesameNumerousbuyersandsellerssothateachhasnoinfluenceoverpriceBuyersandSellersarepricetakersPerfectCompetition竞争:完全及其它产品是完全相同的。买者和卖者如此之多，以至于没有一个买者或卖者可以影响价格。买者和卖者都是价格接受者。完全竞争Competition:PerfectandOtherwiseMonopolyOneseller,andsellercontrolspriceOligopolyFewsellersNotalwaysaggressivecompetition竞争:完全及其它垄断一个卖者，卖者决定价格。寡头少数几个卖者。并不总是主动地进行竞争。Competition:PerfectandOtherwiseMonopolisticCompetitionManysellersSlightlydifferentiatedproductsEachsellermaysetpriceforitsownproduct竞争:完全及其它垄断竞争许多卖者略有差异的产品每个卖者都有决定自己产品价格的能力Demand需求Quantitydemanded

istheamount

ofagoodthatbuyersarewillingandabletopurchase.

需求量是指买者愿意而且能够购买的一种物品或劳务的数量。LawofDemand需求规律Thelawofdemandstatesthatthereisaninverserelationshipbetweenpriceandquantitydemanded.

需求规律认为，价格与需求量之间的关系是负关系。DemandSchedule需求表Thedemandscheduleisatablethatshowstherelationshipbetweenthe

price

ofthegoodandthe

quantity

demanded.

需求表

——

表示一种物品的价格与需求量之间关系的表格。Catherine’sDemandSchedule凯瑟琳的需求表DemandCurve需求曲线The

demandcurve

is

thedownward-slopinglinerelatingpricetoquantitydemanded.需求曲线——把价格与需求量联系在一起的向右下方倾斜的曲线。Figure1Catherine’sDemandSchedule

andDemandCurvePriceofIce-CreamCone02.502.001.501.000.501234567891011QuantityofIce-CreamCones$3.00121.Adecreaseinprice...2....increasesquantityofconesdemanded.图1.Catherine的需求表和需求曲线冰激凌蛋卷的价格02.502.001.501.000.501234567891011冰激凌蛋卷需求量$3.00121.价格下降…

2....蛋卷的需求量上升。MarketDemandversusIndividualDemandMarketdemandreferstothesumofallindividualdemandsforaparticulargoodorservice.Graphically,individualdemandcurvesaresummedhorizontallytoobtainthemarketdemandcurve.市场需求市场需求是指所有个人对某种物品或劳务需求的总和。从图形上看,把个人需求曲线水平相加，就得出了市场需求曲线。ChangeinQuantityDemandedversusChangeinDemandChangein

QuantityDemandedMovementalongthedemandcurve.Causedbyachangeinthepriceof theproduct.需求量的变化与需求的变化需求量的变化沿着需求曲线移动。是由于产品价格变动引起的。0DPriceofIce-Cream

ConesQuantityofIce-CreamConesAtaxthatraisesthepriceofice-creamconesresultsinamovementalongthedemandcurve.AB81.00$2.004ChangesinQuantityDemanded0D冰激凌蛋卷的价格冰激凌蛋卷的消费量提高冰激凌蛋卷价格的税收引起沿着需求曲线的移动AB81.00$2.004需求量的变化ShiftsintheDemandCurveConsumerincomePricesofrelatedgoodsTastesExpectationsNumberofbuyers需求曲线的移动消费者收入相关产品价格嗜好预期买者数量ShiftsintheDemandCurveChangeinDemandAshiftinthedemandcurve,either totheleftorright.Causedbyachangeina determinantotherthantheprice.需求曲线的移动需求的变化需求曲线的移动，向左或者向右。是由价格以外的因素变化引起的。ShiftsintheDemandCurve0D1PriceofIce-CreamConeQuantityofIce-CreamConesD3D2IncreaseindemandDecreaseindemand需求曲线的移动0D1冰激凌蛋卷的价格冰激凌蛋卷的数量D3D2需求增加需求减少ConsumerIncome消费者收入Asincomeincreasesthedemandforanormalgoodwillincrease.

收入增加，正常商品的需求增加Asincomeincreasesthedemandforaninferiorgoodwilldecrease.

收入增加，劣等品的需求减少ConsumerIncome

NormalGood$3.002.502.001.501.000.50213456789101211PriceofIce-CreamConeQuantityofIce-CreamCones0IncreaseindemandAnincreaseinincome...D1D2消费者收入正常商品$3.002.502.001.501.000.50213456789101211冰激凌蛋卷的价格冰激凌蛋卷的数量0需求增加收入增加...D1D2ConsumerIncome

InferiorGood$3.002.502.001.501.000.50213456789101211PriceofIce-CreamConeQuantityofIce-CreamCones0DecreaseindemandAnincreaseinincome...D1D2消费者收入劣等品$3.002.502.001.501.000.50213456789101211冰激凌蛋卷的价格冰激凌蛋卷的数量0需求减少收入增加...D1D2PricesofRelatedGoods

Substitutes&ComplementsWhenafallinthepriceofonegoodreduces

thedemandforanothergood,thetwogoodsarecalledsubstitutes.Whenafallinthepriceofonegoodincreases

thedemandforanothergood,thetwogoodsarecalledcomplements.相关物品的价格

替代品和互补品当一种物品价格下降减少了另一种物品需求时，这两种物品被称为替代品。当一种物品价格下降增加了另一种物品需求时，这两种物品被称为互补品。Table1VariablesThatInfluenceBuyersCopyright©2004South-Western表1.影响买者的变量变量这些变量的变动将...价格表现为沿着需求曲线的变动收入移动需求曲线相关物品价格移动需求曲线嗜好移动需求曲线预期移动需求曲线买者数量移动需求曲线Supply供给Quantitysupplied

istheamountofagoodthatsellersarewillingandabletosell.

供給量是指卖者愿意而且能够出售的一种物品或劳务的数量。LawofSupply供给规律The

lawofsupply

statesthatthereisadirect(positive)relationshipbetweenpriceandquantity

supplied.供给规律认为，价格与供給量之间的关系是正关系。SupplySchedule供给表The

supplyschedule

is

atablethatshowstherelationshipbetweenthepriceofthegoodandthequantitysupplied.供给表是表示一种物品价格与供給量之间关系的表格。

Ben’sSupplySchedule供给表SupplyCurve供给曲线The

supplycurve

istheupward-slopinglinerelatingpricetoquantitysupplied.

供给曲线——把价格与供給量联系在一起的向右上方倾斜的曲线。Figure5Ben’sSupplySchedule

andSupplyCurvericeofIce-CreamCone02.502.001.501.001234567891011QuantityofIce-CreamCones$3.00120.501.Anincrease

inprice...2....

increasesquantityofconessupplied.图5.Ben供给表与供给曲线冰激凌蛋卷需求量02.502.001.501.001234567891011冰激凌蛋卷的供給量$3.00120.501.价格上升…

2....供給量增加。MarketSupplyversusIndividualSupplyMarketsupplyreferstothesumofallindividualsuppliesforallsellersofaparticulargoodorservice.Graphically,individualsupplycurvesaresummedhorizontallytoobtainthemarketsupplycurve.市场供给市场供给是指某种物品或劳务的所有卖者个人供给的总和。从图形上看,把个人供给曲线水平相加，就得出了市场供给曲线。ShiftsintheSupplyCurveInputpricesTechnologyExpectationsNumberofproducers供给曲线的移动投入要素价格技术预期生产者数量ChangeinQuantitySuppliedversusChangeinSupplyChangeinQuantitySuppliedMovementalongthesupplycurve.Causedbyachangeinthemarketpriceoftheproduct.供給量的变化与供给的变化供給量的变化沿着供给曲线移动。是由于产品的市场价格变动引起的。ChangeinQuantitySupplied15PriceofIce-CreamConeQuantityofIce-CreamCones0S1.00AC$3.00Ariseinthepriceoficecreamconesresultsinamovementalongthesupplycurve.供給量的变化15冰激凌蛋卷的价格冰激凌蛋卷的数量0S1.00AC$3.00冰激凌蛋卷的市场价格上升导致供給量沿着供给曲线的移动。ShiftsintheSupplyCurveChangeinSupplyAshiftinthesupplycurve,eithertotheleftorright.

Causedbyachangeinadeterminantotherthanprice.供給曲线的移动供给的变化供给曲线的移动，向左或者向右。

是由于价格以外的因素变化造成的。Shifts

intheSupplyCurvePriceofIce-CreamConeQuantityofIce-CreamCones0S1S2S3IncreaseinSupplyDecreaseinSupply供给曲线的移动冰激凌蛋卷的价格冰激凌蛋卷的数量0S1S2S3供给增加供给减少Table2VariablesThatInfluenceSellers供給量的变化与供给的变化SUPPLYANDDEMANDTOGETHER

供给与需求的结合Equilibrium

referstoasituationinwhichthepricehasreachedthelevelwherequantitysuppliedequalsquantitydemanded.

市场均衡——

价格水平达到供給量与需求量相等的状态。SupplyandDemandTogetherEquilibriumPriceThepricethatbalancessupplyanddemand.Onagraph,itisthepriceatwhichthesupplyanddemandcurvesintersect.EquilibriumQuantityThequantitythatbalancessupplyanddemand.Onagraphitisthequantityatwhichthesupplyanddemandcurvesintersect.

供给与需求的结合均衡价格使供给与需求平衡的价格。从图形上看，就是供给曲线与需求曲线相交时的价格。均衡数量当价格调整到使供给与需求平衡时的供給量与需求量。从图形上看，就是供给曲线与需求曲线相交时的数量。

SupplyandDemandTogetherDemandScheduleSupplyScheduleAt$2.00,thequantitydemandedisequaltothequantitysupplied!供给与需求的结合需求表供给表在$2.00时,需求量等于供給量!Figure8TheEquilibriumofSupply

andDemandCopyright©2003Southwestern/ThomsonLearningPriceofIce-CreamCone0123456789101112QuantityofIce-CreamCones13EquilibriumquantityEquilibriumpriceEquilibriumSupplyDemand$2.00表8.供给与需求的均衡冰激凌蛋卷需求量0123456789101112冰激凌蛋卷的数量13均衡数量均衡价格均衡供给需求$2.00Figure9MarketsNotinEquilibriumPriceofIce-CreamCone0SupplyDemand(a)ExcessSupplyQuantitydemandedQuantitysuppliedSurplusQuantityofIce-CreamCones4$2.50102.007图9.非均衡状态的市场冰激凌蛋卷需求量0供给需求(a)超额供给需求量供给量过剩冰激凌蛋卷的数量4$2.50102.007EquilibriumSurplusWhenprice>equilibriumprice,thenquantitysupplied>quantitydemanded.Thereisexcesssupplyorasurplus.Supplierswilllowerthepricetoincreasesales,therebymovingtowardequilibrium.均衡过剩当价格高于均衡价格时，供給量大于需求量。

存在超额供给或过剩。

供给者通过降低价格来增加销售，这使价格向其均衡水平变动。EquilibriumShortageWhenprice<equilibriumprice,thenquantitydemanded>thequantitysupplied.

Thereisexcessdemandorashortage.Supplierswillraisethepriceduetotoomanybuyerschasingtoofewgoods,therebymovingtowardequilibrium.均衡短缺当价格低于市场均衡价格时，需求量超过了供給量。

存在着超额需求或短缺。

由于太多卖者要购买太少的物品，供给者将提高价格。因此价格将趋向于市场均衡价格。Figure9MarketsNotinEquilibriumPriceofIce-CreamCone0QuantityofIce-CreamConesSupplyDemand(b)ExcessDemandQuantitysuppliedQuantitydemanded1.5010$2.0074Shortage图9.非均衡状态的市场冰激凌蛋卷需求量0冰激凌蛋卷的数量供给供给(b)超额需求供給量需求量1.5010$2.0074短缺Equilibrium

均衡Lawofsupplyanddemand

需求规律Theclaimthatthepriceofanygoodadjuststobringthequantitysuppliedandthequantitydemandedforthatgoodintobalance.认为任何一种物品价格的调整都会使该物品供求平衡的观点。ThreeStepsToAnalyzingChangesinEquilibriumDecidewhethertheeventshiftsthesupplyordemandcurve(orboth).Decidewhetherthecurve(s)shift(s)totheleftortotheright.Usethesupply-and-demanddiagramtoseehowtheshiftaffectsequilibriumpriceandquantity.分析均衡的三个步骤确定该事件是使供给曲线移动，还是使需求曲线移动，或者使两种曲线都移动。确定曲线是向右移动，还是向左移动。用供求图来考察这种移动如何影响均衡价格和数量。HowanIncreaseinDemandAffectstheEquilibriumPriceofIce-CreamCone2.0007QuantityofIce-CreamConesSupplyInitialequilibriumD11.Hotweatherincreasesthedemandforicecream...D22....resultinginahigherprice...$2.50103....andahigherquantitysold.Newequilibrium需求增加如何影响均衡冰激凌蛋卷的价格2.0007冰激凌蛋卷的数量供给原来的均衡D11.天气热使冰激凌需求增加...D22.…引起价格上升...$2.50103.…及销售量更多。新均衡ThreeStepstoAnalyzingChangesinEquilibrium

ShiftsinCurvesversusMovementsalongCurvesAshiftinthesupplycurveiscalledachangeinsupply.Amovementalongafixedsupplycurveiscalledachangeinquantitysupplied.Ashiftinthedemandcurveiscalledachangeindemand.Amovementalongafixeddemandcurveiscalledachangeinquantitydemanded.分析均衡的三个步骤曲线移动与沿着曲线的移动:供给曲线的移动被称为供给的变化。沿着固定的供给曲线的移动被称为供給量的变化。需求曲线的移动被称为需求的变化。沿着固定的需求曲线的移动被称为需求量的变化。S2HowaDecreaseinSupplyAffectstheEquilibriumPriceofIce-CreamCone2.00012347891112QuantityofIce-CreamCones13DemandInitialequilibriumS1101.Anearthquakereducesthesupplyoficecream...Newequilibrium2....resultinginahigherprice...$2.503....andalowerquantitysold.S2供给减少如何影响均衡冰激凌蛋卷的价格2.00012347891112冰激凌蛋卷的数量13需求原来的均衡S110地震减少了冰激凌的供给...新均衡2.…引起价格上升...$2.503.…以及销售量减少。WhatHappenstoPriceandQuantityWhenSupplyorDemandShifts?当供给或需求变动时，价格和数量

会发生什么变化?SummaryEconomistsusethemodelofsupplyanddemandtoanalyzecompetitivemarkets.Inacompetitivemarket,therearemanybuyersandsellers,eachofwhomhaslittleornoinfluenceonthemarketprice.小结经济学家用供求模型来分析竞争市场。在竞争市场中，有许多买者和卖者，他们当中的任何一个对市场价格具有极小或者没有影响力。SummaryThedemandcurveshowshowthequantityofagooddependsupontheprice.Accordingtothelawofdemand,asthepriceofagoodfalls,thequantitydemandedrises.Therefore,thedemandcurveslopesdownward.Inadditiontoprice,otherdeterminantsofhowmuchconsumerswanttobuyincludeincome,thepricesofcomplementsandsubstitutes,tastes,expectations,andthenumberofbuyers.Ifo