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经济是研究人类行为的科学，作为一种目的和稀缺的手段之间的关系，有替代用途。
Economic is the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses, says Lionel Robbins in a 1932 essay.
The problem of scarcity and choice 稀缺性与选择问题
每一个社会都有可以作为生产性投入的资源。这些有时被称为生产要素。他们经常被划分为土地、劳动力、资本和企业。这些都是用来生产商品和服务。占有和使用这些商品和服务是衡量我们生活水平的一个标准。衡量一个经济体的产品和服务的总产出的衡量被称为国民生产总值。
事实上，我们作为个人，并且同样适用于企业和政府，不能在给定的时间点上，我们想要的一切就是稀缺的经济问题，只有极少数商品可以称为免费商品相对于经济商品如我们呼吸的空气。使用或消耗大部分的资源或物品将涉及一个牺牲，例如，如果你买一本书，那么你使用的钱，你的时间可能已被用于其他东西。被放弃的最好的替代被称为机会成本，在研究决策时是经济学和其他社会科学的一个重要概念。
Every society has resources which can be used as productive inputs. These are sometimes known as factors of production. They are often classified as land, labour, capital and enterprise. These are used to produce goods and services. Possession and use of these goods and services is one measure of our living standards. A measure of an economy's total output of goods and services is known as gross national production.
The fact that we as individuals, and the same applies to companies and to the government, cannot get everything we want at a given point in time is known as the economic problem of scarcity, only a very small number of goods can be called free goods as opposed to economic goods such as the air we breathe. Using or consuming most resources or goods will involve a sacrifice, for instance, if you buy a book then the money you used and the time you took could have been used for something else. The best alternative given up is known as the opportunity cost, and is an important concept in economics and other social sciences when studying decision making.
The concept of opportunity cost 机会成本概念
Making a choice means one thing must be given up to get something else. Every choice is a trade-off, which means giving up something to get something else. Every choice also involves a cost. It is called opportunity cost. Opportunity cost can emphasize the problem of scarcity when making a choice. For instance, you can quit college or university right now or you can stay in education. If you quit and take a job, you might earn money and buy what you want, and spend more free time with friends. If you remain in education, you might not afford these things. You will be able to buy these things later and that is one of the payoffs from being in college. Therefore for now, if you buy books, you might not have enough money left to buy clothes. The opportunity cost of being in college is the alternative things that you would have done if you had quit college.
The difference between micro and macro economic 微观与宏观经济的差异
Microeconomics is the study of the decisions of individual people and businesses and the interaction of those decisions in markets. It seeks to explain the prices and quantities of individual goods and services. Microeconomics also studies the effects of government regulation and taxes on prices and quantities in markets.
Macroeconomics is the study of the national economy and the global economy as a whole. It seeks to explain average prices and the total level of employment, income and production. Macroeconomics also studies the effect of taxes, government spending and the government budget deficit on total employment and incomes. It also examines the effects of money and interest rates.
For example, the difference between the micro and macro perspective is highlighted by Olympics. You can take a micro view of a single participant and the actions he or she is taking, or you can take a macro view by looking at the whole pattern formed by the joint actions of all the individual participants in the display.
Derivation of individual demand curve 个别需求曲线的推导
Individual demand is the relationship between the price of a good and the quantity demanded by a single individual.
Individual people's demand curves for any good will be the same as their marginal utility curve for that good, measured in money. The graph above shows the marginal utility curve for a particular person and a particular good. If the price of the good were P1, the person would consume Q1: where MU=P. Thus point a would be one point on that person's demand curve. If the price fell to P2, consumption would rise to Q2, since it is where MU=P2. Thus point b is a second point on the demand curve. If the price fell to P3, Q3 would be consumed. Point c is a third point on the demand curve.
Therefore as long as individuals consume where P=MU, their demand curve will be along the same line as their marginal utility curve.
Derivation of market demand 市场需求衍生
The market demand curve is the horizontal sum of the individual demand curves formed by adding the quantities demanded by each individual at each price.
People who operate firms make many decision. All of these decisions are aimed at one overriding objective: maximum attainable profit. Decision about the quantity to produce and the price to charge depend on the type of market in which the firm operates.
No one sets up a firm without believing it will be profitable. And profit depends on total revenues and costs. Costs are related to the choice of input used for production.
The firm's short-run output decision 公司的短期产出决策
 We know that the perfectly competitive firm can sell as many units as it wants, as long as it charges the market-determined price. The perfectly competitive firm must decide how much to produce. The firm will choose the quantity where profits are maximized.
We know that profit = total revenue - total cost.
Total revenue (TR) is calculated as price multiplied by quantity. TR = P x q
Marginal revenue (MR) is the added revenue that a firm takes in when it increases output by one additional unit, or MR = (change in TR)/(change in q).
The profit maximizing strategy is for a firm to find out if the additional money it gets from selling one more unit is more than the cost of making one more unit. In other words, the marginal revenue more than the marginal cost, then the firm would want to make one more, because it will make money on that additional unit.
As long as the MR is bigger than the MC, the firm should produce more. Once MR = MC, the firm will want to stop production, because if it increases production, the MC will be bigger than the MR. If MC > MR, then the cost of making one additional unit is more than the amount of money received from selling one additional unit. Thus, the profit-maximizing quantity is where MC = MR.
Output (supply) decisions are less constrained in the long run because the firm has no fixed factor of production and firms are free to enter and exit industries. A firm with a positive profit level is earning an above-normal rate of return, and in the long run, new firms are likely to be attracted into the industry.
Sometimes, though, the best a firm can do, given the market price, might still cause the firm to lose money. A firm that is suffering a loss is earning a rate of return that is below normal, and investors are not going to be attracted to the industry. The firm may also be breaking even, meaning that its profit level is zero. But since profit is total revenue minus total cost, and total cost includes a normal rate of return, the firm that is breaking even is still earning exactly a normal rate of return. New investors may not be attracted, but current ones are not running away either.
The table below summarizes the different circumstances in which a perfectly competitive firm may find itself in the short run.
As it looks to the long run, it must consider how its costs will change with different scales of operation. The analysis of long-run possibilities is even more complex than the short-run analysis, because more things are variable-scale of plant is not fixed and there are no fixed costs. In theory, the firm may choose any scale of operation, and so it must analyze many possible options.
In the long run, entry and exit of firms are possible. If firms in an industry are earning profits, entry is likely. If they are suffering losses, firms will exit. This is the long-run adjustment to the short-run conditions of profit or loss.
How equilibrium price and equilibrium quantity is achieved
An equilibrium is a situation in which opposing forces balance each other, so there is no tendency for change. Market equilibrium occurs when the market price balances the plans of both buyers and sellers. The equilibrium price is the price of which the quantity, demand equals the quantity supplied. The equilibrium quantity is the quantity bought and sold at the equilibrium price. The price of good regulates the quantities demanded and supplied. If the price is too high, the quantity supplied exceeds the quantity demanded. If the price is too low, the quantity exceeds the quantity supplied. There is one price, and only one price, at which the quantity demand equals the quantity supplied. Price will adjust when there is a shortage or a surplus because it is beneficial to both buyers and sellers.#p#分页标题#e#
The effects of excess supply on market equilibrium 供应过剩对市场均衡的影响
A rise in supply causes a surplus and hence a fall in price. This then acts as an incentive for consumers to buy more. A fall in supply causes a rise in price. This then acts as an incentive for consumers to buy less.
The effects of excess demand on market equilibrium
A rise in demand causes a shortage and hence a rise in price. This then acts as an incentive for businesses to supply more. It is profitable for them to do so. They divert resources from products with lower prices relative to cost, and hence lower profits, to the product that has gone up in price and hence is now more profitable.
A fall in demand causes a surplus and hence a fall in price. This then acts as an incentive for businesses to supply less. These goods are now less profitable to produce.
Definition of perfect competition 完全竞争的定义
Economists identify five market types including perfect competition. Perfect competition arises if the minimum efficient scale of a single producer is small relative to the demand for a good or service. The minimum efficient scale is the smallest quantity of output at which long-run average costs reaches its lowest level. Where the minimum efficient scale of a firm is small relative to the demand, there is room for many firms in the industry. Perfect competition also arises when consumers regardless of which firm they buy from. This usually happens when the goods and services produced by any one firm has no distinctive characteristics which differentiate it from the output of other firms in the industry.
Firms in perfect competition make many decisions, but the one decision they never make is the price at which to sell their output. Firms in perfect competition are said to be price takers. A price taker is a firm that cannot influence the price of a good or service. A price-taking firm faces a demand curve that is perfectly elastic.
Definition of oligopoly 寡头垄断的定义
Oligopoly occurs when just a few firms between them share a large proportion of the industry. Most oligopolists produce differentiated products, for examples, cars, soap, powder and soft drinks. Much of the competition between such oligopolists is in terms of the marketing of their particular brand. Because there are only a few firms under oligopoly, each firm will have to take account of the others. This means that they are mutually dependent, they are interdependent. Interdependence under oligopoly is one of the two key features of oligopoly. Each firm will be affected by it rivals' decisions. Likewise its decisions will affect its rivals. Firms recognize this interdependence. This recognition will affect their decisions. Each firm is affected by its rivals' actions. If a firm changes the price or specification of it product or the amount of its advertising, the sales of its rivals will be affected. The rivals may then respond by changing their price, specification or advertising. No firm can therefore afford to ignore the actions and reactions of other firms in the industry.
It is impossible, therefore, to predict the effect on a firm's sales of a change in its price without first making some assumption about the reactions of other firms. Different assumptions will yield different predictions. For this reason there is no single generally accepted theory of oligopoly. Firms may react differently and unpredictably.
Keynesian economics 凯恩斯经济学
Keynesian economics is also called Keynesianism and Keynesian Theory. It is a macroeconomic theory based on the ideas of 20th-century British economist John Maynard Keynes. An economic theory stating that active government intervention in the marketplace and monetary policy is the best method of ensuring economic growth and stability.
He studied at Cambridge but came to reject much of the classical economics and neo-classical economics associated with that university. Keynes helped set up the bretton woods framework, but he is best known for his General Theory of Employment, Interest and Money, published in 1936 in the depths of the Great Depression. This invented modern macroeconomics. It argued that economies could sometimes be stable in equilibrium even when they did not have full employment, but that a government could remedy this under-employment problem by increasing public spending and/or reducing taxation, thereby increasing the level of aggregate demand in the economy. Many politicians picked up on these ideas. As President Richard Nixon observed in 1971, "We are all Keynesians now." However, it is much debated whether Keynes would have supported the way many of them put his thoughts into practice.
Kleptocracy 盗贼统治
Corrupt, thieving government, in which the politicians and bureaucrats in charge use the powers of the state to feather their own nests. Russia in the years immediately after the fall of communism was a clear-cut example, with Mafia-friendly government members allocating themselves valuable shares during the privatisation of state-owned companies, accepting bribes from foreign businesses, not collecting taxes from "helpful" companies and siphoning off international aid into their personal offshore bank accounts.
Monetarism 货币主义
Control the money supply, and the rest of the economy will take care of itself. A school of economic thought that developed in opposition to post-1945 Keynesian policies of demand management, echoing earlier debates between mercantilism and classical economics. Monetarism is based on the belief that inflation has its roots in the government printing too much money. It is closely associated with Milton, who argued, based on the quantity theory of money that government should keep the money supply fairly steady, expanding it slightly each year mainly to allow for the natural growth of the economy. If it did this, market forces would efficiently solve the problems of inflation, unemployment and recession. Monetarism had its heyday in the early 1980s, when economists, governments and investors pounced eagerly on every new money-supply statistic, particularly in the United States and the UK.
Many central banks had set formal targets for money-supply growth, so every wiggle in the data was scrutinised for clues to the next move in the rate of interest. Since then, the notion that faster money-supply growth automatically causes higher inflation has fallen out of favour. The money supply is useful as a policy target only if the relationship between money and nominal GDP, and hence inflation, is stable and predictable. The way the money supply affects prices and output depends on how fast it circulates through the economy. The trouble is that its velocity of circulation can suddenly change. During the 1980s, the link between different measures of the money supply and inflation proved to be less clear than monetarist theories had suggested, and most central banks stopped setting binding monetary targets. Instead, many have adopted explicit inflation targets.
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