3 Substitutes Everywhere The Concept of Demand
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It is a further and very important application of marginal analysis.
12
The Demand Curve：Making it Graphic
Table 3-1 depicts the amount of water people plan to consume, at various prices, in a typical American town. Note:
They’ll strive to “waste less water” .
19
The Law of Demand
“Law of Demand”（需求法则）：
If the price of a good increases, holding other things constant, the quantity demanded will decrease. If the price of a good decreases, holding other things constant, the quantity demanded will increase.
13
The Demand Curve：Consumption Table
Price per Gallon $.07 .04 .02 .01 .005 Gallons per Day 23 40 80 160 320
表3-1
14
The Demand Curve
$.07 .06 PRICE PER GALLON .05 .04 .03 .02 .01 .00
5
Marginal Values
Questions
Which is more valuable, water or diamonds? Which is more valuable, a glass of water or a glass of diamonds?
“钻石与水悖论”
6
Marginal Values
Answers
The values that matter are marginas “additional”
7
Marginal Values
Economic analysis is basically marginal analysis
Consumers make marginal adjustments to changes in the price of water. They don’t normally engage in all-or-nothing trade-offs.
18
The Demand Curve
As economizers, people tend to conserve water when they face higher prices. (当水价 上升时，作为节约者，人们倾向于节约用水.)
The word consume doesn’t necessarily mean they are all trying to drink some quantity of water per day! It simply means they are trying to acquire and use that much water for a variety of different purposes.
9
Everyday Choices Are Marginal Choices
The Economic Way of Thinking…
Rejects the all-or-nothing approach（非此即彼） Favors attention to
Marginal benefits Marginal costs
4
On the Notion of Needs
这4句话均有可能产生严重的误导！
Higher prices (sacrifices) lead people to seek substitutes （替代品）.
The fact that goods and services are scarce entails trade-offs, i.e., the sacrifice of other goods and services we value.
11
The Demand Curve
Demand is a concept that relates amounts people want to obtain to the sacrifices they must make to obtain these amount. (这个概 念把人们想获得某种东西的数量与他们为了得 到这些数量要付出的代价联系在一起.)
2
Chapter Outline
Misperceptions Caused by Inflation Time Is on Our Side Price Elasticity of Demand Elasticity and Total Receipts The Myth of Vertical Demand All Scarce Goods Must Be Rationed – Somehow Is Money All That Matters? Money Costs, Other Costs and Economic Calculation
ceteris paribus: 其他一切相同，拉丁语
20
Demand and Quantity Demanded（需求 和需求量）
In using the concept of demand, you must be alert for the possibility that something else has changed in addition to the price.（使用需 求概念时，必须注意，除了价格变动以外，其 他因素也发生了变动这种可能性.） “ A change in demand” is not the same thing as a “change in quantity demanded.”
“The Economic Way of Thinking” 12th Edition
Chapter 3 Substitutes Everywhere: The Concept of Demand
学习目的
•掌握需求概念和需求法则
1
Chapter Outline
Introduction On the Notion of “Needs” Marginal Values Everyday Choices – Marginal Choices The Demand Curve The Law of Demand Demand and Quantity Demanded Demand Itself Can Change Everything Depends Upon Everything Else
21
Demand and Quantity Demanded
A change in quantity demanded is a movement from one point on a curve to another point on the same curve.
Results from price change
Nothing matters in economic decision making except marginal benefits and marginal costs.
8
Everyday Choices Are Marginal Choices
It’s usually more of this and less of that versus more of that and less of this, measured from the position in which we find ourselves when called on to decide. （当我们做选择时，通常会发现，情况往往是 这样：从当时的境况出发，此多彼少或者此少 彼多.）
0
40
80
120
160
200
240 280
320
360
400
GALLONS OF WATER PER DAY
15
The Demand Curve
Vertical Axis（纵轴） – possible prices that might be charged. Horizontal Axis （横轴） – quantity purchased at those prices. Economists call that a Demand Curve.
More of A and less of B versus more of B and less of A
10
The Demand Curve
The concept of “needs(需要)” encourages allor-nothing thinking and fails to appreciate the idea of marginal thinking.
3
On the Notion of “Needs”（需要）
What is the relationship between “tradeoffs” and “needs”? Consider these four statements…
The average person needs eight glasses of water per day to maintain good health. All citizens should be able to obtain the medical care they need regardless of their ability to pay. A diabetic needs insulin.（糖尿病人需要胰岛 素. ） You need to read your economics textbook.
12
The Demand Curve：Making it Graphic
Table 3-1 depicts the amount of water people plan to consume, at various prices, in a typical American town. Note:
They’ll strive to “waste less water” .
19
The Law of Demand
“Law of Demand”（需求法则）：
If the price of a good increases, holding other things constant, the quantity demanded will decrease. If the price of a good decreases, holding other things constant, the quantity demanded will increase.
13
The Demand Curve：Consumption Table
Price per Gallon $.07 .04 .02 .01 .005 Gallons per Day 23 40 80 160 320
表3-1
14
The Demand Curve
$.07 .06 PRICE PER GALLON .05 .04 .03 .02 .01 .00
5
Marginal Values
Questions
Which is more valuable, water or diamonds? Which is more valuable, a glass of water or a glass of diamonds?
“钻石与水悖论”
6
Marginal Values
Answers
The values that matter are marginas “additional”
7
Marginal Values
Economic analysis is basically marginal analysis
Consumers make marginal adjustments to changes in the price of water. They don’t normally engage in all-or-nothing trade-offs.
18
The Demand Curve
As economizers, people tend to conserve water when they face higher prices. (当水价 上升时，作为节约者，人们倾向于节约用水.)
The word consume doesn’t necessarily mean they are all trying to drink some quantity of water per day! It simply means they are trying to acquire and use that much water for a variety of different purposes.
9
Everyday Choices Are Marginal Choices
The Economic Way of Thinking…
Rejects the all-or-nothing approach（非此即彼） Favors attention to
Marginal benefits Marginal costs
4
On the Notion of Needs
这4句话均有可能产生严重的误导！
Higher prices (sacrifices) lead people to seek substitutes （替代品）.
The fact that goods and services are scarce entails trade-offs, i.e., the sacrifice of other goods and services we value.
11
The Demand Curve
Demand is a concept that relates amounts people want to obtain to the sacrifices they must make to obtain these amount. (这个概 念把人们想获得某种东西的数量与他们为了得 到这些数量要付出的代价联系在一起.)
2
Chapter Outline
Misperceptions Caused by Inflation Time Is on Our Side Price Elasticity of Demand Elasticity and Total Receipts The Myth of Vertical Demand All Scarce Goods Must Be Rationed – Somehow Is Money All That Matters? Money Costs, Other Costs and Economic Calculation
ceteris paribus: 其他一切相同，拉丁语
20
Demand and Quantity Demanded（需求 和需求量）
In using the concept of demand, you must be alert for the possibility that something else has changed in addition to the price.（使用需 求概念时，必须注意，除了价格变动以外，其 他因素也发生了变动这种可能性.） “ A change in demand” is not the same thing as a “change in quantity demanded.”
“The Economic Way of Thinking” 12th Edition
Chapter 3 Substitutes Everywhere: The Concept of Demand
学习目的
•掌握需求概念和需求法则
1
Chapter Outline
Introduction On the Notion of “Needs” Marginal Values Everyday Choices – Marginal Choices The Demand Curve The Law of Demand Demand and Quantity Demanded Demand Itself Can Change Everything Depends Upon Everything Else
21
Demand and Quantity Demanded
A change in quantity demanded is a movement from one point on a curve to another point on the same curve.
Results from price change
Nothing matters in economic decision making except marginal benefits and marginal costs.
8
Everyday Choices Are Marginal Choices
It’s usually more of this and less of that versus more of that and less of this, measured from the position in which we find ourselves when called on to decide. （当我们做选择时，通常会发现，情况往往是 这样：从当时的境况出发，此多彼少或者此少 彼多.）
0
40
80
120
160
200
240 280
320
360
400
GALLONS OF WATER PER DAY
15
The Demand Curve
Vertical Axis（纵轴） – possible prices that might be charged. Horizontal Axis （横轴） – quantity purchased at those prices. Economists call that a Demand Curve.
More of A and less of B versus more of B and less of A
10
The Demand Curve
The concept of “needs(需要)” encourages allor-nothing thinking and fails to appreciate the idea of marginal thinking.
3
On the Notion of “Needs”（需要）
What is the relationship between “tradeoffs” and “needs”? Consider these four statements…
The average person needs eight glasses of water per day to maintain good health. All citizens should be able to obtain the medical care they need regardless of their ability to pay. A diabetic needs insulin.（糖尿病人需要胰岛 素. ） You need to read your economics textbook.
