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1、1,第四章,供给与需求的市场力量 The Market Forces of Supply and Demand,2,供给与需求的市场力量 The Market Forces of Supply 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供给、需求和市场均衡
2、。 Modern microeconomics is about supply, demand, and market equilibrium.,3,市场 Markets,一个市场就是由某种商品或服务的买者和卖者组成的群体。 A market is a group of buyers and sellers of a particular good or service. 术语供给和需求指人们的行为当他们在市场中相互作用时。 The terms supply and demand refer to the behavior of people . . . as they interact wi
3、th one another in markets.,4,市场 Markets,买方决定需求。 Buyers determine demand.,卖方决定供给。 Sellers determine supply.,5,市场类型：竞争市场 Market Type: A Competitive Market,竞争性市场是这样一个市场 A competitive market is a market. . . 拥有众多买者和卖者 with many buyers and sellers. 不受任何一个人操纵 that is not controlled by any one person. 买者和卖
4、者所遵循的价格被确定在窄小的范围内。 in which a narrow range of prices are established that buyers and sellers act upon.,6,竞争：完全竞争与否Competition: Perfect and Otherwise,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、卖者都是价格接受者。 Buyers and
5、Sellers are price takers.,完全竞争 Perfect Competition,7,竞争：完全竞争与否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 sellers,8,竞争：完全竞争与否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 Slig
6、htly differentiated products 每个卖者都能为自己的产品设定价格 Each seller may set price for its own product,9,需求 Demand,需求量是买者愿意而且能够购买的商品数量。 Quantity demanded is the amount of a good that buyers are willing and able to purchase.,10,需求量的决定 Determinants of Quantity Demanded,市场价格 Market price 消费者收入 Consumer income 相关商
7、品的价格 Prices of related goods 嗜好 Tastes 预期 Expectations,11,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 there is an inverse relationship between price and quantity demanded.,12,需求表 Demand Schedule,需求表通过一个表格显示了商品价格与需求量之间的关系。 The demand schedule is a table that shows the relationshi
8、p between the price of the good and the quantity demanded.,13,需求表 Demand Schedule,14,需求曲线 Demand Curve,需求曲线：将价格与需求量联系起来的向右下方倾斜的曲线。 The demand curve is the downward-sloping line relating price to quantity demanded.,15,需求曲线 Demand Curve,$3.00,2.50,2.00,1.50,1.00,0.50,2,1,3,4,5,6,7,8,9,10,12,11,冰激凌蛋卷的价
9、格Price of Ice-Cream Cones,冰激凌蛋卷的需求数量 Quantity of Ice-Cream Cones,0,16,“其他条件不变” Ceteris Paribus,Ceteris paribus 是一个拉丁习惯用语，意思是除了被研究的变量之外，其余所有变量均假定为恒定不变。字面意义是“其他条件不变（相同）”。 Ceteris paribus is a Latin phrase that means all variables other than the ones being studied are assumed to be constant. Literally,
10、 ceteris paribus means “other things being equal.”,需求曲线向下倾斜是因为，在其他条件不变的情况下，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!,17,“其他条件不变” Ceteris Paribus,影响某个内生变量（例如需求量）的外生变量一般说来有很多个（价格、收入、偏好等）。 “其他条件不变”刻画了特定的某一外生变量对内生变量的影响（相当于微积分
11、中的偏导数）。 经济学谈论的因果关系都暗含“其他条件不变”。,18,“其他条件不变” Ceteris Paribus,“其他条件不变”意味着，不能简单地从内生变量的改变，推断某一个外生变量确定的改变。 例子：以下说法是否正确？ “既然价格升高导致需求量减少；那么，如果观察到需求量减少，一定是价格升高了。” “既然过量饮食导致体重增加；那么，体重增加一定是由过量饮食引起的。”,19,市场需求 Market Demand,市场需求指的是所有个人对某种商品或劳务的需求总和。 Market demand refers to the sum of all individual demands for a
12、 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.,20,市场需求 Market Demand,21,需求的变化与需求量的变化 Change in Quantity Demanded versus Change in Demand,需求量的变化 Change in Quantity Demanded 由该产品价格的变动所引起。 Caused
13、 by a change in the price of the product. 沿着需求曲线的移动。 Movement along the demand curve.,22,需求量的变动 Changes in Quantity Demanded,0,D1,每包香烟 的价格 Price of Cigarettes per Pack,每天抽烟的数量 Number of Cigarettes Smoked per Day,税收抬高了香烟价格，引致了需求量由A到C沿着需求曲线运动。 A tax that raises the price of cigarettes results in a mov
14、ement along the demand curve.,A,20,2.00,23,需求量变化与需求变化 Change in Quantity Demanded versus Change in Demand,需求变化 Change in Demand 由该物品价格之外的其他决定因素引起。 Caused by a change in a determinant other than the price. 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.,24,需求的变化 Changes in Demand,0,D1,价格 Price of Ice-Cream Cone,数量 Quantity of Ice-Cream Cones,D3,D2,需求增加Increase in demand,需求减少Decrease in demand,25,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
