Perfect competition

In economic theory, perfect competition describes markets such that no participants are large enough to have the market power to set the price of a homogeneous product. Because the conditions for perfect competition are strict, there are few if any perfectly competitive markets. Still, buyers and sellers in some auction-type markets, say for commodities or some financial assets, may approximate the concept. Perfect competition serves as a benchmark against which to measure real-life and imperfectly competitive markets. Basic structural characteristics Generally, a perfectly competitive market exists when every participant is a "price taker", and no participant influences the price of the product it buys or sells. Specific characteristics may include: Infinite buyers and sellers Ц An infinite number of consumers with the willingness and ability to buy the product at a certain price, and infinite producers with the willingness and ability to supply the product at a certain price. Zero entry and exit barriers Ц A lack of entry and exit barriers makes it extremely easy to enter or exit a perfectly competitive market. Perfect factor mobility Ц In the long run factors of production are perfectly mobile, allowing free long term adjustments to changing market conditions. Perfect information - All consumers and producers are assumed to have perfect knowledge of price, utility, quality and production methods of products. Zero transaction costs - Buyers and sellers do not incur costs in making an exchange of goods in a perfectly competitive market. Profit maximization - Firms are assumed to sell where marginal costs meet marginal revenue, where the most profit is generated. Homogenous products - The qualities and characteristics of a market good or service do not vary between different suppliers. Non-increasing returns to scale - The lack of increasing returns to scale (or economies of scale) ensures that there will always be a sufficient number of firms in the industry. Property rights - Well defined property rights determine what may be sold, as well as what rights are conferred on the buyer. In the short run, perfectly-competitive markets are not productively efficient as output will not occur where marginal cost is equal to average cost (MC=AC). They are allocatively efficient, as output will always occur where marginal cost is equal to marginal revenue (MC=MR). In the long run, perfectly competitive markets are both allocatively and productively efficient. In perfect competition, any profit-maximizing producer faces a market price equal to its marginal cost (P=MC). This implies that a factor's price equals the factor's marginal revenue product. It allows for derivation of the supply curve on which the neoclassical approach is based. This is also the reason why "a monopoly does not have a supply curve". The abandonment of price taking creates considerable difficulties for the demonstration of a general equilibrium except under other, very specific conditions such as that of monopolistic competition. In the short run, it is possible for an individual firm to make an economic profit. This situation is shown in this diagram, as the price or average revenue, denoted by P, is above the average cost denoted by C . However, in the long period, economic profit cannot be sustained. The arrival of new firms or expansion of existing firms (if returns to scale are constant) in the market causes the (horizontal) demand curve of each individual firm to shift downward, bringing down at the same time the price, the average revenue and marginal revenue curve. The final outcome is that, in the long run, the firm will make only normal profit (zero economic profit). Its horizontal demand curve will touch its average total cost curve at its lowest point. (See cost curve.) In a perfectly competitive market, a firm's demand curve is perfectly elastic. As mentioned above, the perfect competition model, if interpreted as applying also to short-period or very-short-period behaviour, is approximated only by markets of homogeneous products produced and purchased by very many sellers and buyers, usually organized markets for agricultural products or raw materials. In real-world markets, assumptions such as perfect information cannot be verified and are only approximated in organized double-auction markets where most agents wait and observe the behaviour of prices before deciding to exchange (but in the long-period interpretation perfect information is not necessary, the analysis only aims at determining the average around which market prices gravitate, and for gravitation to operate one does not need perfect information). In the absence of externalities and public goods, perfectly competitive equilibria are Pareto-efficient, i.e. no improvement in the utility of a consumer is possible without a worsening of the utility of some other consumer. This is called the First Theorem of Welfare Economics. The basic reason is that no productive factor with a non-zero marginal product is left unutilized, and the units of each factor are so allocated as to yield the same indirect marginal utility in all uses, a basic efficiency condition (if this indirect marginal utility were higher in one use than in other ones, a Pareto improvement could be achieved by transferring a small amount of the factor to the use where it yields a higher marginal utility).

Monopoly violates this optimal allocation condition, because in a monopolized industry market price is above marginal cost, and this means that factors are underutilized in the monopolized industry, they have a higher indirect marginal utility than in their uses in competitive industries. Of course this theorem is considered irrelevant by economists who do not believe that general equilibrium theory correctly predicts the functioning of market economies; but it is given great importance by neoclassical economists and it is the theoretical reason given by them for combating monopolies and for antitrust legislation.