This chapter is the first of three closely related chapters analyzing the four basic market models—pure competition, pure monopoly, monopolistic competition, and oligopoly.  Here the market models are introduced and explained, which makes this the longest and perhaps most difficult of the three chapters.

Explanations and characteristics of the four models are outlined at the beginning of this chapter.  Then the characteristics of a purely competitive industry are detailed.  There is an introduction to the concept of the perfectly elastic demand curve facing an individual firm in a purely competitive industry.  Next, the total, average, and marginal revenue schedules are presented in numeric and graphic form.  Using the cost schedules from the previous chapter, the idea of profit maximization is explored.

The total-revenue—total-cost approach is analyzed first because of its simplicity.  More space is devoted to explaining the MR = MC rule, and to demonstrating that this rule applies in all market structures, not just in pure competition.

Next, the firm’s short‑run supply schedule is shown to be the same as its marginal-cost curve at all points above the average-variable-cost curve.  Then the short‑run competitive equilibrium is discussed at the firm and industry levels.

The long‑run equilibrium position for a competitive industry is shown by reviewing the process of entry and exit in response to relative profit levels in the industry.  Long‑run supply curves and the conditions of constant, increasing, and decreasing costs are explored.

Finally, the chapter concludes with a detailed evaluation of pure competition in terms of productive and allocative efficiency (P = minimum ATC, and P = MC).


After completing this chapter, students should be able to

      1.    List the four basic market models and characteristics of each.

      2.    Describe characteristics of a purely competitive firm and industry.

      3.    Explain how a purely competitive firm views demand for its product and marginal revenue from each additional unit sale.

      4.    Compute average, total, and marginal revenue when given a demand schedule for a purely competitive firm.

      5.    Use both total-revenue—total-cost and marginal-revenue—marginal-cost approaches to determine short‑run price and output that maximizes profits (or minimizes losses) for a competitive firm.

      6.    Find the short‑run supply curve when given short‑run cost schedules for a competitive firm.

      7.    Explain how to construct an industry short‑run supply curve from information on single competitive firms in the industry.

      8.    Explain the long‑run equilibrium position for a competitive firm using the entry and exit of firms to explain adjustments from nonequilibrium positions.

      9.    Explain the shape of long‑run industry supply curves in constant‑cost and increasing‑cost industries.

  10.    Differentiate between productive and allocative efficiency.

  11.    Explain why allocative efficiency and productive efficiency are achieved where P = minimum AC = MC.

  12.    Define and identify terms and concepts listed at the end of the chapter.

I.          Four market models will be addressed in Chapters 23‑25; characteristics of the models are summarized in Table 23-1.

A.  Pure competition entails a large number of firms, standardized product, and easy entry (or exit) by new (or existing) firms.

B.   At the opposite extreme, pure monopoly has one firm that is the sole seller of a product or service with no close substitutes; entry is blocked for other firms.

C.   Monopolistic competition is close to pure competition, except that the product is differentiated among sellers rather than standardized, and there are fewer firms.

D.  An oligopoly is an industry in which only a few firms exist, so each is affected by the price‑output decisions of its rivals.

II.        Pure Competition:  Characteristics and Occurrence

A.  The characteristics of pure competition.

1.   Many sellers means that there are enough so that a single seller has no impact on price by its decisions alone.

2.   The products in a purely competitive market are homogeneous or standardized; each seller’s product is identical to its competitor’s.

3.   Individual firms must accept the market price; they are price takers and can exert no influence on price.

4.   Freedom of entry and exit means that there are no significant obstacles preventing firms from entering or leaving the industry.

5.   Pure competition is rare in the real world, but the model is important.

a.   The model helps analyze industries with characteristics similar to pure competition.

b.   The model provides a context in which to apply revenue and cost concepts developed in previous chapters.

c.   Pure competition provides a norm or standard against which to compare and evaluate the efficiency of the real world.

B.   There are four major objectives to analyzing pure competition.

1.   To examine demand from the seller’s viewpoint

2.   To see how a competitive producer responds to market price in the short run

3.   To explore the nature of long‑run adjustments in a competitive industry

4.   To evaluate the efficiency of competitive industries

III.       Demand from the Viewpoint of a Competitive Seller

A.  The individual firm will view its demand as perfectly elastic.

1.   Table 23-2 and Figures 23-1 and 23-7a illustrate this.

2.   The demand curve is not perfectly elastic for the industry: It only appears that way to the individual firm, since it must take the market price no matter what quantity it produces.

3.   Note from Figure 23-1 that a perfectly elastic demand curve is a horizontal line at the price.

B.   Definitions of average, total, and marginal revenue.

1.   Average revenue is the price per unit for each firm in pure competition.

2.   Total revenue is the price multiplied by the quantity sold.

3.   Marginal revenue is the change in total revenue and will also equal the unit price in conditions of pure competition.  (Key Question 3)

IV.       Profit Maximization in the Short Run: Two Approaches

A.  In the short run the firm has a fixed plant and maximizes profits or minimizes losses by adjusting output; profits are defined as the difference between total costs and total revenue.

B.   Three questions must be answered.

1.   Should the firm produce?

2.   If so, how much?

3.   What will be the profit or loss?

C.   An example of the total‑revenue—total‑cost approach is shown in Table 23-3.  Note that the costs are the same as for the firm in Table 22-2 in the previous chapter.

1.   The firm should produce if the difference between total revenue and total cost is profitable, or if the loss is less than the fixed cost.

2.   In the short run, the firm should produce that output at which it maximizes its profit or minimizes its loss.

3.   The profit or loss can be established by subtracting total cost from total revenue at each output level.

4.   The firm should not produce, but should shut down in the short run if its loss exceeds its fixed costs.  Then, by shutting down its loss will just equal those fixed costs.

5.   A graphical representation is shown in Figures 23-2a and b.  Note: The firm has no control over the market price.

D.  Marginal‑revenue—marginal‑cost approach (see Table 23-4 and Figure 23-3).

1.   The MR = MC rule states that the firm will maximize profits or minimize losses by producing at the point at which marginal revenue equals marginal cost in the short run.

2.   Three features of this MR = MC rule are important.

a.   The rule assumes that marginal revenue must be equal to or exceed minimum-average-variable cost or firm will shut down.

b.   The rule works for firms in any type of industry, not just pure competition.

c.   In pure competition, price = marginal revenue, so in purely competitive industries the rule can be restated as the firm should produce that output where P = MC, because P = MR.

3.   Using the rule on Table 23-4, compare MC and MR at each level of output.  At the tenth unit MC exceeds MR. Therefore, the firm should produce only nine (not the tenth) units to maximize profits.

4.   Profit-maximizing case:  The level of profit can be found by multiplying ATC by the quantity, 9, to get $880 and subtracting that from total revenue which is $131 x 9 or $1179.  Profit will be $299 when the price is $131.  Profit per unit could also have been found by subtracting $97.78 from $131 and then multiplying by 9 to get $299.  Figure 23.3 portrays this situation graphically.

5.   Loss-minimizing case: The loss‑minimizing case is illustrated when the price falls to $81.  Table 23-5 is used to determine this.  Marginal revenue does exceed average variable cost at some levels, so the firm should not shut down.  Comparing P and MC, the rule tells us to select an output level of 6.  At this level the loss of $64 is the minimum loss this firm could realize, and the MR of $81 just covers the MC of $80, which does not happen at a quantity level of 7.  Figure 23-4 is a graphical portrayal of this situation.

6.   Shut-down case:  If the price falls to $71, this firm should not produce.  MR will not cover AVC at any output level.  Therefore, the minimum loss is the fixed cost and production of zero.  Table 23-5 and Figure 23-5 illustrate this situation, and it can be seen that the $100 fixed cost is the minimum possible loss.

7.   CONSIDER THIS … The Still There Motel

E.   Marginal cost and the short‑run supply curve can be illustrated by hypothetical prices such as those in Table 23-6.  At a price of $151 profit will be $480; at $111 the profit will be $138 ($888‑$750); at $91 the loss will be $3.01; at $61 the loss will be $100 because the latter represents the close-down case.

1.   Note that Table 23-6 gives us the quantities that will be supplied at several different price levels in the short-run.

2.   Since a short‑run supply schedule tells how much quantity will be offered at various prices, this identity of marginal revenue with the marginal cost tells us that the marginal cost above AVC will be the short‑run supply for this firm (see Figure 23-6).

F.   Changes in prices of variable inputs or in technology will shift the marginal cost or short-run supply curve in Figure 23-6.

1.   A wage increase would shift the supply curve upward.

2.   Technological progress would shift the marginal cost curve downward.

3.   Using this logic, a specific tax would cause a decrease in the supply curve (upward shift in MC), and a unit subsidy would cause an increase in the supply curve (downward shift in MC).

G.   Determining equilibrium price for a firm and an industry:

1.   Total-supply and total-demand data must be compared to find the most profitable price and output levels for the industry.  (See Table 23-7.)

2.   Figure 23-7a and b shows this analysis graphically; individual firm supply curves are summed horizontally to get the total-supply curve S in Figure 23-7b.  If product price is $111, industry supply will be 8000 units, since that is the quantity demanded and supplied at $111.  This will result in economic profits similar to those portrayed in Figure 23-3.

3.   A loss situation similar to Figure 23-4 could result from weaker demand (lower price and MR) or higher marginal costs.

H.  Firm vs. industry: Individual firms must take price as given, but the supply plans of all competitive producers as a group are a major determinant of product price.  (Key Question 4)

V.         Profit Maximization in the Long Run

A.  Several assumptions are made.

1.   The entry and exit of firms are the only long‑run adjustments.

2.   Firms in the industry have identical cost curves.

3.   The industry is a constant‑cost industry, which means that the entry and exit of firms will not affect resource prices or location of unit‑cost schedules for individual firms.

B.   The basic conclusion to be explained is that after long‑run equilibrium is achieved, the product price will be exactly equal to, and production will occur at, each firm’s point of minimum average total cost.

1.   Firms seek profits and shun losses.

2.   Under competition, firms may enter and leave industries freely.

3.   If short‑run losses occur, firms will leave the industry; if economic profits occur, firms will enter the industry.

C.   The model is one of zero economic profits, but note that this allows for a normal profit to be made by each firm in the long run.

1.   If economic profits are being earned, firms enter the industry, which increases the market supply, causing the product price to gravitate downward to the equilibrium price where zero economic profits are earned (Figure 23-8).

2.   If losses are incurred in the short run, firms will leave the industry; this decreases the market supply, causing the product price to rise until losses disappear and normal profits are earned (Figure 23-9).

D.  Long‑run supply for a constant cost industry will be perfectly elastic; the curve will be horizontal.  In other words, the level of output will not affect the price in the long run.

1.   In a constant‑cost industry, expansion or contraction does not affect resource prices or production costs.

2.   The entry or exit of firms will affect quantity of output, but will always bring the price back to the equilibrium price (Figure 23-10).

E.   Long‑run supply for an increasing cost industry will be upward sloping as the industry expands output.

1.   Average‑cost curves shift upward as the industry expands and downward as the industry contracts, because resource prices are affected.

2.   A two‑way profit squeeze will occur as demand increases because costs will rise as firms enter, and the new equilibrium price must increase if the level of profit is to be maintained at its normal level.  Note that the price will fall if the industry contracts as production costs fall, and competition will drive the price down so that individual firms do not realize above‑normal profits (see Figure 23-11).

F.   Long‑run supply for a decreasing-cost industry will be downward sloping as the industry expands output.  This situation is the reverse of the increasing‑cost industry.  Average‑cost curves fall as the industry expands and firms will enter until price is driven down to maintain only normal profits.  (Key Question 7)

VI.       Pure Competition and Efficiency

A.  Whether the industry is one of constant, increasing, or decreasing costs, the final long‑run equilibrium will have the same basic characteristics (Figure 23-12).

1.   Productive efficiency occurs where P = minimum AC; at this point firms must use the least‑cost technology or they won’t survive.

2.   Allocative efficiency occurs where P = MC, because price is society’s measure of relative worth of a product at the margin or its marginal benefit.  And the marginal cost of producing product X measures the relative worth of the other goods that the resources used in producing an extra unit of X could otherwise have produced.  In short, price measures the benefit that society gets from additional units of good X, and the marginal cost of this unit of X measures the sacrifice or cost to society of other goods given up to produce more of X.

3.   If price exceeds marginal cost, then society values more units of good X more highly than alternative products the appropriate resources can otherwise produce.  Resources are underallocated to the production of good X.

4.   If price is less than marginal cost, then society values the other goods more highly than good X, and resources are overallocated to the production of good X.

5.   Efficient allocation occurs when price and marginal cost are equal.  Under pure competition this outcome will be achieved.

6.   Dynamic adjustments will occur automatically in pure competition when changes in demand or in resource supplies or in technology occur.  Disequilibrium will cause expansion or contraction of the industry until the new equilibrium at P = MC occurs.

7.   “The invisible hand” works in a competitive market system since no explicit orders are given to the industry to achieve the P = MC result.

VII.      LAST WORD:  Pure Competition and Consumer Surplus

A.  In almost all markets, consumers collectively obtain more utility (total satisfaction) from their purchases than the amount of their expenditures (product price x quantity).

B.   Since pure competition establishes the lowest price consistent with continued production, it yields the largest sustainable amount of consumer surpluses.