Perfect Competition

Perfect Competition is a theoretical market structure that serves as a benchmark for efficiency. It is defined by the following characteristics:

Many Buyers and Sellers: The number of firms in the market is so large that each individual firm's output is negligible compared to the total market supply. Similarly, there are many buyers.
Homogeneous (Identical) Products: All firms sell a product that is perfectly interchangeable with the product of any other firm. Consumers perceive the products as identical (e.g., specific raw commodities like wheat or milk). This means there is no basis for non-price competition.
Perfect Knowledge/Information: All market participants (buyers and sellers) have complete and accurate information about prices, costs, and market conditions. No firm can charge a higher price, as buyers immediately know of cheaper alternatives.
Freedom of Entry and Exit (No Barriers to Entry or Exit): In the long run, firms can enter or leave the market without incurring significant costs or facing any legal, financial, or technical obstacles. This is the crucial characteristic that ensures long-run normal profit.
Firms are Price Takers: Due to the large number of firms and the homogeneous product, no single firm can influence the market price. The market determines the price ($P$), and the individual firm must accept it.

The Firm's Demand Curve

Because the firm is a price taker, its demand curve is perfectly elastic (horizontal) at the market-determined price.

This means Price (P) = Marginal Revenue (MR) = Average Revenue (AR).
The firm can sell any quantity at the market price, but nothing at a price even slightly higher.

Profit Maximizing Equilibrium in the Short Run and Long Run

Firms in perfect competition, like all firms, aim to maximize profit by producing where Marginal Revenue (MR) = Marginal Cost (MC).

Short-Run Equilibrium

In the short run, the number of firms is fixed. The individual firm faces a market price ($PM) determined by the industry's supply and demand. The firm can earn supernormal profit, normal profit, or economic losses.

Supernormal Profit:

Condition: P = AR > ATC (Average Total Cost) at the profit-maximising output (MR=MC). In the diagram, this is the Demand curve at price level 2, where the Average Revenue is greater than the Average Costs.
Result: The firm's revenue covers all explicit and implicit costs (including normal profit), with a surplus remaining.

Normal Profit (Break-Even):

Condition: P = AR = ATC at the profit-maximising output (MR=MC). This is the point on the graph where the Demand curve is on price level 1, directly tangent to the average cost.
Result: The firm covers all its costs, earning the minimum return required to keep the entrepreneur in the business.

Economic Loss:

Condition: P = AR < ATC at the profit-maximising output (MR=MC). This is the demand curve level where price level is P3, and the the average revenue is less than average cost.
Short-Run Shut-Down Rule: The firm will continue to produce only if P > AVC (Average Variable Cost). If the price covers variable costs, the firm minimizes its loss by contributing to fixed costs. If P < AVC, the firm should shut down immediately.

Long-Run Equilibrium

The key to the long run is the characteristic of free entry and exit. This mechanism drives profits to a stable normal level.

If firms are earning Supernormal Profit:

The prospect of high profits attracts new firms to enter the industry.
The market supply curve shifts right, causing the market price (PM) to fall.
The process continues until the price falls to a level where all firms are only earning normal profit.

If firms are incurring Economic Losses:

Firms will exit the industry, as they can't even cover the opportunity cost of their resources.
The market supply curve shifts left, causing the market price (PM) to rise.
The process continues until the price rises to a level where the remaining firms are just covering their costs, earning normal profit.

Long-Run Equilibrium Condition:

In the long run, the firm produces where:

Result: All firms earn only normal profit.
Long-Run Shut-Down Point: If price falls permanently below the minimum ATC, firms will exit the market.