Chapter 9: Classical and Keynesian Theories I. Classical and Keynesian theories of Aggregate Spending



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Chapter 9: Classical and Keynesian Theories

I. Classical and Keynesian theories of Aggregate Spending


  1. Classical Theory believes that full-employment is the employment level the economy will return to, and tends to remain at in the long run. Graphically, the pure Classical theorists would have a vertical AS curve that shows the same GDP (GDP*) associated with full-employment, at each price-level in the economy.

  2. Keynesian Theory holds that unemployment is the normal state of the economy and significant government intervention is required if employment/output targets are to be reached. In this view, AS is horizontal.

  3. The Classical reasoning:

    1. Say’s law: Supply creates its own Demand. This reflects the “simple circular-flow model,” that had firms employing all the resources (which are owned by households) and the costs of these inputs is the income people use to buy all of the output firms produce.

    2. Abstinence Theory of Interest: To a great extent, it is the interest rate that influences people’s savings. Money they do not spend (savings) becomes part of the supply in the market for loanable funds. The quantity (horizontal axis) is dollars lent out; the price of loanable funds is the interest rate. Business investment spending (I) is also dependent on the interest rate, which will cause S=I in the long run.

    3. Classical theorists held that wages and prices would change proportionately. For example, imagine the prevailing salary is $100,000 a year, and firms have hired so many people at that cost because demand is very high, causing output to increase – and more labor hired shrinks the pool of those unemployed. This becomes an expansion that is not sustainable, above long-run potential AS, which is vertical. All the spending in the economy and the input costs getting passed on to consumers both cause prices to rise. High prices in the product market signal AD to shift left and high wage rates (input costs) cause layoffs (firm decrease output).

In a recession Classical theorists believed a 20% reduction in wages (to $80,000) would mean a 20% decrease in prices as well. Through wage-price flexibility, output could be maintained at the long run level.


  1. Keynesian critique of Classical Theories

(John Maynard Keynes 1883-1946)

    1. Say’s Law – Does better describing the conditions in which it was written (18th Century France) than industrialized economies. Modern economies have decentralized production but often profit makers are remote and far from the production. Many employees never buy their firm’s products, and wages have an effect on costs, but not the firm’s revenue (total sales). There are many ways to increase Demand more effectively than to push for more output to be produced.

    2. Abstinence Theory of Interest – to the idea that I=S at the market clearing interest rate, Keynes argued that Investors and savers have different motivations. Rather than just the interest rate, their decision on how much to save or invest depends on other factors:

      1. Savings may be based on a regular amount being put aside for retirement. It may be for a purchase in the near future (car, house, college fund)

      2. Investment depends on firms’ expectations about GDP, Prices, Industry demand



    1. Wage-Price Flexibility – monopoly power of suppliers restricts flexibility in prices. Unions restricts flexibility in wages. In deflation, debt worsens (becomes more costly to the debtor in real terms). Because people are more aware of nominal than real savings, any decrease in the price-level would have to be dramatic to cause consumption to increase. (The Classical notion of the Pigou Effect stated that falling prices increase asset value and make people feel wealthier and consume more)

Central Keynesian Conclusions:



  1. AD determines Real GDP

  2. In the short run, AD can be adjusted to achieve target GDP and unemployment levels with prices not changing (fixed, flat prices)

  3. When operating at a level other than capacity GDP (Y*) there are no forces to automatically restore Y*

Usually, either unemployment (low Demand) or inflation (high Demand) exist.

One of the major implications of Keynesian conclusion is that government involvement (through active fiscal policy) is essential to achieve Y*. Therefore some economists regard Keynes as a modern-day “mercantilist” referring to the theory that governments should be responsible for economic welfare.

II. AS-AD Analysis

A. Aggregate Demand-Aggregate Supply (AD-AS) Analysis

1. AD is the measure of entire planned spending on final goods and services at each level of prices and RGDP.

i. The AD-AS graph is similar to the Demand and Supply for a single good. However, on the horizontal axis is RGDP (real output, instead of Quantity of the single good) and the vertical axis is the price level (tracked by an index like the CPI).

ii. At the equilibrium price level (where AD and AS cross) real output that AD plans to purchase equals the output AS plans to produce.

iii. AD is determined by the four spending sectors. In other words these are AD’s SHIFT FACTORS:

1. Consumption is influenced by several factors. Some of the most important are Disposable Income (which will change if taxes change), Availability of credit (indicated by the interest rate, which is determined in the market for loanable funds-meaning credit), and consumer expectations.

2. Investment spending depends largely on interest rates, government policies regarding business, and expectations.

3. Government expenditures are often built in to the budget, although Congress and the President can make substantial changes in the level and type of spending that goes on. They may implement new spending programs that are to be automatically countercyclical, or eliminate existing “automatic stabilizers.” The automatic stabilizer would be any policy that

a.) Is Countercyclical:

It would lead to expansionary fiscal policy (such as Government spending increases) in bad economies and contractionary fiscal policies (like tax increases) in good economies.

b.) Is Automatic

It fluctuates (without any new legislation needed) in immediate response to a change in income. Examples: Income-Security payments (G rises when Y falls), progressive income tax system (T rises when Y rises).

4. Net Exports are influenced by:

i. Trade Policy. Existence of tariffs or quotas on imports will decrease the imports flowing into a country. So if a U.S. trading partner restricts the quantity of a certain good they will import from us, that “quota” will decrease our exports. The same is true if this trading partner imposes a “tariff,” a tax on the imported goods.
ii. Exchange rates. If the dollar is cheaper relative to foreign currencies, our exports will increase because US producers (who want to be paid in dollars) are now making goods that the rest of the world finds cheaper.

Net Exports (X-M) will also increase because M (imports) decreases in this example since foreign goods have become more expensive due to the fact that the dollar does not go as far in purchasing the foreign currency.

iii. Politics. Sometimes laws abroad will limit the profitability and income US producers can make there by requiring that part of the production be owned by companies in their country.

A demand shock will shift the entire AD curve if there is a curve in C, I, G, or Xn.

Some positive shocks to aggregate demand would be: Tax cut for individuals (C increases), Interest rate cute (C and I increase), or G increasing. Shocks that would shift AD to the left including worsening consumer expectations (C decreases) or consumers buying more imports (Xn decreases).

B. Why does AD slope downward?

1. Downward Sloping Due to:

i.The wealth effect

If the nominal value of everyone in a country’s Assets=A, then Real Assets would be expressed as A/P or nominal assets over the price level (P). Moving down (to a lower price level) in the AD diagram is associated with more output demanded since the real value of people’s wealth (assets) has increased. Some of that increase in purchasing power will stimulate increased goods and services purchases, thus moving horizontally in response to the fall in Prices

ii. The Interest Rate Effect

Real Money balances M/P increase with a fall in P, meaning the real value of the money supply (to be detailed in Chapter 11) increases and banks have more to lend out. The increase in loanable funds decreases the price of those funds: the interest rate. This means more output demanded (horizontal movement in the AD response to the falling Price level) as consumer loans and business debt increase to finance more purchases. Remember the low (falling) inflation, or even deflation, enables banks to charge lower nominal interest rates and still get a stable real interest rate on loans.

iii. International effect

Ceteris Paribus, if prices are falling in the U.S. for domestically produced goods, we’ll be buying fewer imports (increasing Aggregate Quantity Demanded)

iv. Multiplier Effect

Detailed in Chapter 10, it amplifies the other effects because of the “rounds of spending” that occur when an exogenous shock, positive or negative, to some spending sector plays out over the near future. For example, if the government raises taxes, that will restrain consumer spending, and C is a major portion of expenditures. But the story doesn’t end there, because the lost spending is lost revenue for many businesses and individuals who will in turn cut back a bit on their own spending and some saving. But these people who have responded to the revenue loss now set off the next group of businesses and individuals who would have received the spending, and they respond just the same. It may be more intuitive to think of a positive exogenous shock, like a stock market boom.
C. Aggregate Supply

As measures the entire desired output of final goods and services at each level of prices and RGDP. The shocks that can shift AS are

1. Input costs, and the availability of resources.

2. Capacity of capital and other factors of production

3. Investment plans (inversely related to the interest rate)

Directly relates to the level of capacity utilization

4. Technology.

5. Productivity

6. Expectations – about a variety of indications including the price level, consumer spending, and industry conditions.

7. Gov’t policies. An increase in regulations and laws hindering and putting conditions on private sector output will be a negative shock to AS while deregulation would be a positive shock.


The book adds to these: Excise and Sales taxes and import prices as shifters, which, along with those listed above, comprise shift factors for SAS or Short-run AS.

LAS or Long-run AS can only be shifted by a real change in # of available inputs ((2) above, or (4) and (5) above which make existing inputs produce at a higher level of potential output.

Therefore 2, 4 and 5 shift both SAS and LAS, which is easiest to draw with a kinked AS where both the diagonal and vertical portions shift right.
D. The Upward slope of the AS curve is due to diminishing productivity of resources. As prices rise and firms strive to take in more profits by producing more output, they have to hire more factors of production. The additional labor is not as productive as the original workers who have been working there longer and were the first people the company decided to hire due to their skills. The additional workers decrease the average productivity per worker, making costs rise as output rises.

In the opposite direction, moving down along an AS curve, less demand putting downward pressure on prices signals to suppliers they should produce less. They layoff workers who are generally the less productive, less senior, lower skilled of their workers. The increase in average productivity lowers costs to the firm and makes them willing to offer the decreased level of output at lower prices.

E. The AS curve is best understood as having three distinct “ranges” the first being horizontal, the second diagonal, and the third vertical. The vertical portion is the full-employment range, and it follows a vertical line straight up from the potential output level (the RGDP* if the economy is at the natural rate of unemployment).

AD can increase through the full-employment range, but it will only raise prices, not RGDP.



Bottlenecks are associated with the diagonal portion; the economy can produce more, but producers experience productivity loss and thus higher costs that are getting passed on to consumers. RGDP and the price level both increase as AD moves to the right through this region.

The horizontal portion is “Unemployment” where output can be increased by whatever amount AD requires with no increase in prices.


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