In contrast to a monopoly or oligopoly, it is impossible for a firm in perfect competition to earn economic profit in the long run, which is to say that a firm cannot make any more money than is necessary to cover its economic costs. In order not to misinterpret this zero-long-run-profits thesis, it must be remembered that the term 'profit' is also used in other ways. Neoclassical theory defines profit as what is left of revenue after all costs have been subtracted, including normal interest on capital plus the normal excess over it required to cover risk, and normal salary for managerial activity. Classical economists on the contrary defined profit as what is left after subtracting costs except interest and risk coverage; thus, if one leaves aside risk coverage for simplicity, the neoclassical zero-long-run-profit thesis would be re-expressed in classical parlance as profits coinciding with interest in the long period, i.e. the rate of profit tending to coincide with the rate of interest. Profits in the classical meaning do not tend to disappear in the long period but tend to normal profit. With this terminology, if a firm is earning abnormal profit in the short term, this will act as a trigger for other firms to enter the market. As other firms enter the market the market supply curve will shift out causing prices to fall. Existing firms will react to this lower price by adjusting their capital stock downward.[7] This adjustment will cause their marginal cost to shift to the left causing the market supply curve to shift inward.[7] However, the net effect of entry by new firms and adjustment by existing firms will be to shift the supply curve outward.[7] The market price will be driven down until all firms are earning normal profit only.[8] It is important to note that perfect competition is a sufficient condition for allocative and productive efficiency, but it is not a necessary condition. Laboratory experiments in which participants have significant price setting power and little or no information about their counterparts consistently produce efficient results given the proper trading institutions.[9] [edit]The shutdown point In the short run, a firm operating at a loss [R < TC (revenue less than total cost) or P < ATC (price less than unit cost)] must decide whether to continue to operate or temporarily shutdown.[10] The shutdown rule states "in the short run a firm should continue to operate if price exceeds average variable costs."[11] Restated, the rule is that for a firm to continue producing in the short run it must earn sufficient revenue to cover its variable costs.[12] The rationale for the rule is straightforward. By shutting down a firm avoids all variable costs.[13] However, the firm must still pay fixed costs.[14] Because fixed cost must be paid regardless of whether a firm operates they should not be considered in deciding whether to produce or shutdown. Thus in determining whether to shut down a firm should compare total revenue to total variable costs (VC) rather than total costs (FC + VC). If the revenue the firm is receiving is greater than its total variable cost (R > VC) then the firm is covering all variable cost plus there is additional revenue ("contribution"), which can be applied to fixed costs. (The size of the fixed costs is irrelevant as it is a sunk cost. The same consideration is used whether fixed costs are one dollar or one million dollars.) On the other hand if VC > R then the firm is not even covering its production costs and it should immediately shut down. The rule is conventionally stated in terms of price (average revenue) and average variable costs. The rules are equivalent (If you divide both sides of inequality TR > TVC by Q gives P > AVC). If the firm decides to operate, the firm will continue to produce where marginal revenue equals marginal costs because these conditions insure not only profit maximization (loss minimization) but also maximum contribution. Another way to state the rule is that a firm should compare the profits from operating to those realized if it shutdown and select the option that produces the greater profit.[15][16] A firm that is shutdown is generating zero revenue and incurring no variable costs. However, the firm still has to pay fixed cost. So the firm's profit equals fixed costs or ?FC.[17] An operating firm is generating revenue, incurring variable costs and paying fixed costs. The operating firm's profit is R ? VC ? FC. The firm should continue to operate if R ? VC ? FC ? ?FC, which simplified is R ? VC.[18][19] The difference between revenue, R, and variable costs, VC, is the contribution to fixed costs and any contribution is better than none. Thus, if R ? VC then firm should operate. If R < VC the firm should shut down. A decision to shut down means that the firm is temporarily suspending production. It does not mean that the firm is going out of business (exiting the industry).[20]] If market conditions improve, and prices increase, the firm can resume production. Shutting down is a short-run decision. A firm that has shut down is not producing. The firm still retains its capital assets; however, the firm cannot leave the industry or avoid its fixed costs in the short run. Exit is a long-term decision. A firm that has exited an industry has avoided all commitments and freed all capital for use in more profitable enterprises.[21] However, a firm cannot continue to incur losses indefinitely. In the long run, the firm will have to earn sufficient revenue to cover all its expenses and must decide whether to continue in business or to leave the industry and pursue profits elsewhere. The long-run decision is based on the relationship of the price and long-run average costs. If P ? AC then the firm will not exit the industry. If P < AC, then the firm will exit the industry. These comparisons will be made after the firm has made the necessary and feasible long-term adjustments. In the long run a firm operates where marginal revenue equals long-run marginal costs.[22] [edit]Short-run supply curve The short run supply curve for a perfectly competitive firm is the marginal cost (MC) curve at and above the shutdown point. Portions of the marginal cost curve below the shut down point are not part of the SR supply curve because the firm is not producing in that range. Technically the SR supply curve is a discontinuous function composed of the segment of the MC curve at and above minimum of the average variable cost curve and a segment that runs with the vertical axis from the origin to but not including a point "parallel" to minimum average variable costs.[23] [edit]Examples Though there is no actual perfectly competitive market in the real world, a number of approximations exist: Perhaps the closest thing to a perfectly competitive market would be a large auction of identical goods with all potential buyers and sellers present. By design, a stock exchange resembles this, not as a complete description (for no markets may satisfy all requirements of the model) but as an approximation. The flaw in considering the stock exchange as an example of Perfect Competition is the fact that large institutional investors (e.g. investment banks) may solely influence the market price. This, of course, violates the condition that "no one seller can influence market price". Horse betting is also quite a close approximation. When placing bets, consumers can just look down the line to see who is offering the best odds, and so no one bookie can offer worse odds than those being offered by the market as a whole, since consumers will just go to another bookie. This makes the bookies price-takers. Furthermore, the product on offer is very homogeneous, with the only differences between individual bets being the pay-off and the horse. Of course, there are not an infinite amount of bookies, and some barriers to entry exist, such as a license and the capital required to set up. Free software works along lines that approximate perfect competition as well. Anyone is free to enter and leave the market at no cost. All code is freely accessible and modifiable, and individuals are free to behave independently. Free software may be bought or sold at whatever price that the market may allow. Some believe[who?] that one of the prime examples of a perfectly competitive market anywhere in the world is street food in developing countries. This is so since relatively few barriers to entry/exit exist for street vendors. Furthermore, there are often numerous buyers and sellers of a given street food, in addition to consumers/sellers possessing perfect information of the product in question. It is often the case that street vendors may serve a homogenous product, in which little to no variations in the product's nature exist. Another very near example of perfect competition would be the fish market and the vegetable or fruit vendors who sell at the same place, the bars in "Le Carre" (Liege, Belgium) or the "kebab street" near the Grand Place in Brussels[24]: There are large number of buyers and sellers. There are no entry or exit barriers. There is perfect mobility of the factors, i.e. buyers can easily switch from one seller to the other. The products are homogenous. [edit]Criticisms The use of the assumption of perfect competition as the foundation of price theory for product markets is often criticized as representing all agents as passive, thus removing the active attempts to increase one's welfare or profits by price undercutting, product design, advertising, innovation, activities that - the critics argue – characterize most industries and markets. These criticisms point to the frequent lack of realism of the assumptions of product homogeneity and impossibility to differentiate it, but apart from this the accusation of passivity appears correct only for short-period or very-short-period analyses, in long-period analyses the inability of price to diverge from the natural or long-period price is due to active reactions of entry or exit. Some economists have a different kind of criticism concerning perfect competition model. They are not criticizing the price taker assumption because it makes economic agents too "passive", but because it then raises the question of who sets the prices. Indeed, if everyone is price taker, there is the need for a benevolent planner who gives and sets the prices, in other word, there is a need for a "price maker". Therefore, it makes the perfect competition model appropriate not to describe a decentralize "market" economy but a centralized one. This in turn means that such kind of model has more to do with communism than capitalism.[25] Another frequent criticism is that it is often not true that in the short run differences between supply and demand cause changes in price; especially in manufacturing, the more common behaviour is alteration of production without nearly any alteration of price.[26] The critics of the assumption of perfect competition in product markets seldom question the basic neoclassical view of the working of market economies for this reason. The Neo-Austrian school insists strongly on this criticism, and yet the neoclassical view of the working of market economies as fundamentally efficient, reflecting consumer choices and assigning to each agent his contribution to social welfare, is esteemed to be fundamentally correct[27] Some non-neoclassical schools, like Post-Keynesians, reject the neoclassical approach to value and distribution, but not because of their rejection of perfect competition as a reasonable approximation to the working of most product markets; the reasons for rejection of the neoclassical 'vision' are different views of the determinants of income distribution and of aggregated demand.[28] In particular, the rejection of perfect competition does not generally entail the rejection of free competition as characterizing most product markets; indeed it has been argued[29] that competition is stronger nowadays than in 19th century capitalism, owing to the increasing capacity of big conglomerate firms to enter any industry: therefore the classical idea of a tendency toward a uniform rate of return on investment in all industries owing to free entry is even more valid today; and the reason why General Motors, Texon or Nestle do not enter the computers or pharmaceutical industries is not insurmountable barriers to entry but rather that the rate of return in the latter industries is already sufficiently in line with the average rate of return elsewhere as not to justify entry. On this few economists, it would seem, would disagree, even among the neoclassical ones. Thus when the issue is normal, or long-period, product prices, differences on the validity of the perfect competition assumption do not appear to imply important differences on the existence or not of a tendency of rates of return toward uniformity as long as entry is possible, and what is found fundamentally lacking in the perfect competition model is the absence of marketing expenses and innovation as causes of costs that do enter normal average cost. The issue is different with respect to factor markets. Here the acceptance or denial of perfect competition in labour markets does make a big difference to the view of the working of market economies. One must distinguish neoclassical from non-neoclassical economists. For the former, absence of perfect competition in labour markets, e.g. due to the existence of trade unions, impedes the smooth working of competition, which if left free to operate would cause a decrease of wages as long as there were unemployment, and would finally ensure the full employment of labour: labour unemployment is due to absence of perfect competition in labour markets. Most non-neoclassical economists deny that a full flexibility of wages would ensure the full employment of labour and find a stickiness of wages an indispensable component of a market economy, without which the economy would lack the regularity and persistence indispensable to its smooth working. This was, for example, John Maynard Keynes's opinion. Particularly radical is the view of the Sraffian school on this issue: the labour demand curve cannot be determined hence a level of wages ensuring the equality between supply and demand for labour does not exist, and economics should resume the viewpoint of the classical economists, according to whom competition in labour markets does not and cannot mean indefinite price flexibility as long as supply and demand are unequal, it only means a tendency to equality of wages for similar work, but the level of wages is necessarily determined by complex sociopolitical elements; custom, feelings of justice, informal allegiances to classes, as well as overt coalitions such as trade unions, far from being impediments to a smooth working of labour markets that would be able to determine wages even without these elements, are on the contrary indispensable because without them there would be no way to determine wages.[30] [edit]Equilibrium in perfect competition Equilibrium in perfect competition is the point where market demands will be equal to market supply. A firm's price will be determined at this point. In the short run, equilibrium will be affected by demand. In the long run, both demand and supply of a product will affect the equilibrium in perfect competition. A firm will receive only normal profit in the long run at the equilibrium point.