北大经济学原理第四课

第四章供给与需求的市场力量The Market Forces of Supply andDemand1本章内容需求曲线供给曲线市场均衡和价格机制比较静态(Comparative Statics) ：均衡的变动2供给与需求的市场力量The Market Forces ofSupply and Demand供给与需求是经济学家最常用的两个术语Supply and demand are the two words that economists use most often.供给与需求是推动市场经济运转的力量所在Supply and demand are the forces that make market economies work.现代微观经济学研究有关供给、需求和市场均衡Modern microeconomics is about supply, demand, and market equilibrium.3市场Markets一个市场就是一个购买或销售某种商品或服务的群体A market is a group of buyers and sellers of a particular good or service.术语供给和需求是指市场里人们相互作用的行为The terms supply and demand refer to the behavior of people . . . as they interact with one another in markets.4市场Markets买方形成需求Buyers determine demand.卖方形成供给Sellers determine supply.5市场类型：竞争市场Market Type:A Competitive Market竞争性市场是一个A competitive market is a market. . .拥有众多买者和卖者的市场不受任何一个人操纵的市场买者和卖者遵循市场价格6竞争：完全竞争及其他Competition:Perfect and Otherwise完全竞争Perfect Competition物品完全相同Products are the same买者、卖者如此众多以至于个人无法对价格施加影响.Numerous buyers and sellers so that each has no influence over price买者、卖者都是价格接收者Buyers and Sellers are price takers7竞争：完全竞争及其他Competition:Perfect and Otherwise垄断Monopoly只有一个卖者，它控制价格One seller, and seller controls price寡头Oligopoly少数几个卖者Few sellers8竞争：完全竞争及其他Competition:Perfect and Otherwise垄断竞争Monopolistic Competition许多卖者Many sellers存在微小差别的产品Slightly differentiated products每个卖者都能为自己的产品设定价格Eachseller may set price for its own product9需求Demand需求量是买者愿意而且能够购买的商品数量Quantity demandedis the amountof a good that buyers arewilling and ableto purchase.10需求定律Law of Demand需求定律：价格与需求量负相关The law of demand states that thereis an inverse relationship betweenprice and quantity demanded.11需求表Demand Schedule需求表显示了商品价格与需求量之间的关系The demand schedule is a tablethat shows the relationshipbetween the price of the goodand the quantity demanded.12需求表Demand Schedule价格Price数量Quantity$0.00 120.50 101.00 81.50 62.00 42.50 23.00 013需求的确定Determinants of Demand市场价格Market price消费者收入Consumer income相关商品的价格Prices of related goods嗜好Tastes预期Expectations14需求曲线Demand Curve需求曲线：在以价格为纵轴、需求量为横轴的坐标系里向右下方倾斜的曲线The demand curve is the downward-sloping line relating price to quantity demanded.1516需求曲线Demand Curve $3.002.502.001.501.000.50213456789101211冰激凌蛋卷的价格Price of Ice-Cream Cone冰激凌蛋卷的需求数量Quantity of Ice-Cream Cones 0价格Price 数量Quantity $0.00 12 0.50 101.00 8 1.50 62.00 42.50 23.00 017在“其他条件相同”的情况下Ceteris Paribus Ceteris paribus 是一个拉丁习惯用语，意思是除了被研究的变量外，其余所有变量均假定相同。

字面意义是“其余的均相同”Ceteris paribus is a Latin phrase that means all variables other than the ones being studied are assumed to be constant. Literally,ceteris paribusmeans “other things being equal.”需求曲线向下倾斜是因为，在其他条件相同的情况下，较低的价格意味着较大的需求量The demand curve slopes downward because, ceteris paribus, lower prices imply a greater quantity demanded!市场需求Market Demand市场需求指的是所有个人对某种商品或服务的需求总和Market demand refers to the sum of all individual demands for a particular good or service.从图形上看，个人需求曲线在水平上加总便得到市场需求曲线Graphically, individual demand curves are summed horizontally to obtain the market demand curve.18需求量的变化与需求的变化Change in Quantity Demanded versus Change in Demand需求量的变化Change in Quantity Demanded沿着需求曲线的移动Movement along the demand curve.由该产品价格的变动所引起Caused by a change in the price of the product.1920需求量的变动Changes in QuantityDemanded0D 1每包香烟的价格Price of Cigarettes per Pack每天抽烟的数量Number ofCigarettes Smoked per Day 税收抬高了香烟价格，引致了需求量由A 到C 的运动。

A tax that raises the price of cigarettes results in a movement along the demand curve.AC 202.00$4.0012需求量变化与需求变化Change in Quantity Demandedversus Change in Demand需求变化Change in Demand需求曲线发生移动，要么左移，要么右移A shift in the demand curve, either to the left or right.由不同于该物品价格的其他决定因素引起Caused by a change in a determinant other than the price.2122需求的变化Changes in Demand0D 1价格Price of Ice-Cream Cone数量Quantityof Ice-Cream Cones D 3D 2需求增加Increase in demand需求递减Decrease in demand消费者收入Consumer Income随着收入的增加，对正常品的需求会增加As income increases the demand for a normal good will increase.随着收入的增加，对劣等品（低档品）的需求会减少As income increases the demand for an inferior good will decrease.2324消费者收入：正常品Consumer Income ：Normal Good $3.002.502.001.501.000.50213456789101211Price of Ice-Cream ConeQuantity of Ice-Cream Cones 0需求增加Increase in demand 收入增加…An increasein income...D 1D 225消费者收入：劣等品Consumer Income ：Inferior Good $3.002.502.001.501.000.50213456789101211Price of Ice-Cream ConeQuantity of Ice-Cream Cones 0需求递减Decrease in demand收入增加…An increasein income...D 1D 2相关物品的价格Prices of Related Goods替代品和互补品Substitutes & Complements当一种商品的价格下跌减少了对另一种商品的需求，这两种商品被称为替代品When a fall in the price of one good reduces the demand for another good, the two goods are called substitutes.当一种商品的价格下跌增加了对另一种商品的需求，这两种商品被称为互补品When a fall in the price of one good increases the demand for another good, the two goods are called complements.26需求量变动与需求变动Change in Quantity Demanded versus Change inDemand影响需求量的变量Variables that Affect Quantity Demanded这些变量的变动将A Change in This Variable . . .价格Price代表沿需求曲线的移动Represents a movementalong the demand curve收入Income需求曲线的移动Shifts the demand curve 相关商品价格Prices of related goods嗜好Tastes预期Expectations需求曲线的移动购买者人数Number of buyers需求曲线的移动需求曲线的移动Shifts the demand curve 需求曲线的移动Shifts the demand curve供给Supply供给量是卖者愿意而且能够出售的数量Quantity supplied is the amount of a good that sellers are willing and able to sell.28供给定律Law of Supply供给定律陈述了价格与供给量之间的正相关性。