经济学理论

utility is a representation of preferences over some set of goods and services. Preferences have a utility representation so long as they are transitive, complete, and continuous.

Utility is usually applied by economists in such constructs as the indifference curve, which plot the combination of commodities that an individual or a society would accept to maintain a given level of satisfaction. Individual utility and social utility can be construed as the value of a utility function and a social welfare function respectively. When coupled with production or commodity constraints, under some assumptions, these functions can be used to analyze Pareto efficiency, such as illustrated byEdgeworth boxes in contract curves. Such efficiency is a central concept in welfare economics.

the marginal utility of a good or service is the gain (or loss) from an increase (or decrease) in the consumption of that good or service. Economists sometimes speak of a law of diminishing marginal utility, meaning that the first unit of consumption of a good or service yields more utility than the second and subsequent units. The marginal decision rule states that a good or service should be consumed at a quantity at which the marginal utility is equal to the marginal cost.

The concept of marginal utility played a crucial role in the marginal revolution of the late 19th century, and led to the replacement of the labor

theory of value by neoclassical value theory in which the relative prices of goods and services are simultaneously determined by marginal rates of substitution in consumption and marginal rates of transformation in production, which are equal in economic equilibrium.

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.

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.

The formula may be used in the analysis:

Profit=TR-TC

Marginal Revenue=Change in total revenue/Change in quantity