📚 Pre-U Cambridge Economics: Core Concepts Overview | Pre-U Cambridge 经济：核心知识点梳理
The Cambridge Pre-U Economics syllabus demands a comprehensive grasp of both microeconomic and macroeconomic theory, along with the ability to evaluate real-world policy. This revision guide distils the core topics — from the fundamental economic problem to development economics — into a concise, bilingual overview tailored for exam success.
剑桥 Pre-U 经济学大纲要求透彻掌握微观与宏观理论，并能评估现实政策。本复习指南将核心主题——从基本经济问题到发展经济学——凝练成简明中英双语概览，助力考生应试。
1. Scarcity and Choice | 稀缺与选择
The central economic problem is scarcity: finite resources cannot satisfy infinite human wants. This compels economic agents — individuals, firms, and governments — to make choices, each of which involves an opportunity cost, defined as the next best alternative forgone.
经济学的核心问题是稀缺性：有限的资源无法满足无限的人类欲望。这迫使经济主体（个人、企业和政府）做出选择，每一次选择都涉及机会成本，即所放弃的次优替代选项。
A production possibility curve (PPC) illustrates the concepts of trade-offs, opportunity cost, and efficiency. Points on the curve represent full and efficient resource use, while points inside indicate underemployment. An outward shift of the PPC signals long-run economic growth, often driven by increases in the quantity or quality of factors of production.
生产可能性曲线（PPC）说明了权衡、机会成本与效率等概念。曲线上各点代表资源充分利用且高效，曲线内各点表示资源未充分利用。PPC 向外移动表明长期经济增长，通常由生产要素数量增加或质量提高驱动。
2. Demand and Supply | 需求与供给
The law of demand states that, ceteris paribus, as price falls, quantity demanded rises, and vice versa. This inverse relationship is captured by a downward-sloping demand curve. Determinants of demand include income, tastes, prices of substitutes and complements, and expectations.
需求定律指出，在其他条件不变时，价格下降则需求量上升，反之亦然。这种反向关系表现为一条向下倾斜的需求曲线。需求的决定因素包括收入、偏好、替代品与互补品价格以及预期。
The law of supply posits a direct relationship: as price rises, quantity supplied typically increases, reflected in an upward-sloping supply curve. Key determinants of supply are costs of production, technology, taxes and subsidies, and the number of firms in the market.
供给定律则是一种正向关系：价格上升时供给量通常增加，表现为向上倾斜的供给曲线。供给的关键决定因素有生产成本、技术、税收与补贴以及市场上企业数量。
3. Elasticity | 弹性
Price elasticity of demand (PED) measures the responsiveness of quantity demanded to a change in price: PED = %ΔQd / %ΔP. When |PED| > 1, demand is elastic; when |PED| < 1, demand is inelastic. Knowledge of PED helps firms predict the impact of price changes on total revenue.
需求价格弹性（PED）衡量需求量对价格变动的反应程度：PED = %ΔQd / %ΔP。当 |PED| > 1 时，需求富有弹性；当 |PED| < 1 时，需求缺乏弹性。了解 PED 有助于企业预测价格变化对总收入的影响。
Income elasticity of demand (YED = %ΔQd / %ΔY) classifies goods as normal (YED > 0) or inferior (YED < 0). Cross-price elasticity of demand (XED = %ΔQd x / %ΔPy) reveals whether goods are substitutes (XED > 0) or complements (XED < 0). Price elasticity of supply (PES) depends on the flexibility of production and time period.
需求收入弹性（YED = %ΔQd / %ΔY）将商品分为正常品（YED > 0）或劣质品（YED < 0）。需求的交叉价格弹性（XED = %ΔQd x / %ΔPy）揭示商品是替代品（XED > 0）还是互补品（XED < 0）。供给价格弹性（PES）取决于生产的灵活性和时间周期。
4. Market Equilibrium and Efficiency | 市场均衡与效率
Market equilibrium occurs where quantity demanded equals quantity supplied, yielding an equilibrium price and quantity. Disequilibrium — excess supply or demand — exerts pressure on prices to adjust back to equilibrium.
市场均衡出现在需求量等于供给量时，产生均衡价格和数量。非均衡——超额供给或超额需求——会给价格带来调整压力，直至恢复均衡。
Consumer surplus is the difference between what consumers are willing to pay and what they actually pay; producer surplus is the difference between the price received and the minimum price at which producers are willing to supply. At competitive equilibrium, total welfare (consumer plus producer surplus) is maximised, achieving allocative efficiency where P = MC.
消费者剩余是消费者愿意支付的价格与实际支付价格之间的差额；生产者剩余是实际售价与生产者愿意接受的最低价格之间的差额。在竞争均衡下，总福利（消费者剩余加生产者剩余）达到最大，实现配置效率，即 P = MC。
5. Market Failure | 市场失灵
Market failure occurs when the free market fails to allocate resources efficiently, leading to a net welfare loss. Principal sources include externalities, public goods, information asymmetries, and market power.
市场失灵是指自由市场未能有效配置资源，从而造成净福利损失。主要来源包括外部性、公共品、信息不对称和市场势力。
Negative externalities (e.g. pollution) cause over-production because private costs are lower than social costs. Positive externalities (e.g. education) lead to under-production because private benefits are lower than social benefits. Public goods are non-excludable and non-rival, resulting in the free-rider problem. Imperfect information can lead to adverse selection and moral hazard.
负外部性（如污染）导致过度生产，因为私人成本低于社会成本。正外部性（如教育）导致生产不足，因为私人收益低于社会收益。公共品具有非排他性和非竞争性，产生搭便车问题。不完全信息可能导致逆向选择和道德风险。
6. Government Intervention | 政府干预
Governments use taxation to internalise externalities: an indirect tax equal to the marginal external cost can correct a negative externality. Subsidies, set equal to marginal external benefit, can promote goods with positive externalities. Other tools include regulations, tradable permits, and direct provision of public goods.
政府运用税收将外部性内部化：等于边际外部成本的间接税可以纠正负外部性。等于边际外部收益的补贴能促进正外部性商品。其他工具包括法规、可交易许可证和公共品的直接提供。
Price controls — maximum prices (ceilings) to protect consumers, and minimum prices (floors) to support producers — can create shortages or surpluses if set away from equilibrium. Governments must also consider government failure, where intervention leads to a less efficient outcome than the market.
价格管制——最高限价保护消费者，最低限价支持生产者——若远离均衡设定，可能造成短缺或过剩。政府还需考虑政府失灵，即干预导致比市场更无效的结果。
7. Costs of Production and Market Structures | 生产成本与市场结构
In the short run, firms face both fixed and variable costs. Key cost concepts include marginal cost (MC), average total cost (ATC), average variable cost (AVC). When MC < ATC, ATC falls; when MC > ATC, ATC rises. The long-run average cost curve reflects economies and diseconomies of scale.
短期内，企业面临固定成本和可变成本。关键成本概念有边际成本（MC）、平均总成本（ATC）和平均可变成本（AVC）。当 MC < ATC 时，ATC 下降；当 MC > ATC 时，ATC 上升。长期平均成本曲线反映规模经济与不经济。
| Market Structure | Key Features | Long-run Profit |
|---|---|---|
| Perfect Competition | Many firms, homogeneous goods, free entry/exit, price takers | Normal profit (P = min ATC) |
| Monopoly | Single seller, high barriers, price maker | Supernormal profit possible |
| Oligopoly | Few firms, strategic interdependence, high concentration ratio | Supernormal profit if collusion succeeds |
| Monopolistic Competition | Many firms, differentiated products, low barriers | Normal profit in long run |
市场结构特征与长期利润对比：完全竞争（众多企业，同质产品，自由进出，价格接受者）长期仅获正常利润；垄断（单一卖方，高壁垒，制定价格）可能获超额利润；寡头（少数企业，战略相互依存）合谋成功时获超额利润；垄断竞争（众多企业，产品差异，低壁垒）长期获正常利润。
8. Macroeconomic Objectives | 宏观经济目标
Governments typically pursue four key macroeconomic goals: sustainable economic growth, low and stable inflation (often targeted around 2%), low unemployment, and a sustainable balance of payments position. These objectives can occasionally conflict, requiring trade-offs — for example, rapid growth may fuel inflation.
政府通常追求四大宏观经济目标：可持续经济增长、低且稳定的通胀（常见目标约 2%）、低失业率以及可持续的国际收支状况。这些目标有时会冲突，需要取舍——例如快速增长可能推高通胀。
Economic growth is measured by the rate of change in real GDP. Inflation is tracked via the Consumer Price Index (CPI) or Retail Price Index (RPI). Unemployment is gauged by the claimant count or labour force survey. The current account balance summarises trade in goods, services, income and transfers.
经济增长以实际 GDP 变化率衡量。通胀通过消费者价格指数（CPI）或零售价格指数（RPI）跟踪。失业通过申请失业救济人数或劳动力调查衡量。经常账户余额概括了货物、服务、收入和转移项目的交易。
9. Aggregate Demand and Aggregate Supply | 总需求与总供给
Aggregate demand (AD) is the total spending on domestic output at each price level: AD = C + I + G + (X – M). The AD curve slopes downward due to the wealth effect, interest-rate effect, and net export effect. Shifts in AD can be caused by changes in consumer confidence, fiscal policy, monetary policy, or global demand.
总需求（AD）是在每一价格水平下对国内产出的总支出：AD = C + I + G + (X – M)。AD 曲线向下倾斜的原因包括财富效应、利率效应和净出口效应。AD 的移动可由消费者信心变化、财政政策、货币政策或全球需求变动引起。
Short-run aggregate supply (SRAS) is positively sloped because of sticky wages and misperceptions. Long-run aggregate supply (LRAS) is vertical at the full-employment level of output, determined by the quantity and quality of factors of production. Shocks and policies can shift both SRAS and LRAS, affecting equilibrium price level and real GDP.
短期总供给（SRAS）因工资粘性和认知偏差而呈正斜率。长期总供给（LRAS）在充分就业产出水平上垂直，由生产要素的数量和质量决定。冲击和政策可使 SRAS 和 LRAS 移动，从而影响均衡价格水平和实际 GDP。
10. Fiscal and Monetary Policy | 财政与货币政策
Fiscal policy involves government manipulation of taxation and spending to influence AD. Expansionary policy (increased G or lower taxes) can boost output during a recession, while contractionary policy can cool an overheating economy. Automatic stabilisers, such as progressive taxes and welfare benefits, operate without discretionary action.
财政政策涉及政府操控税收和支出来影响 AD。扩张性政策（增加 G 或减税）可在衰退期提振产出，紧缩性政策可为过热经济降温。自动稳定器，如累进税和福利津贴，无需斟酌行动即可运作。
Monetary policy uses interest rates, money supply, and quantitative easing to manage AD. Central banks typically target inflation by adjusting the policy rate. Lower interest rates encourage borrowing and investment, shifting AD right; higher rates discourage spending. The transmission mechanism operates through credit, exchange rate, and wealth channels.
货币政策运用利率、货币供给和量化宽松管理 AD。中央银行通常通过调整政策利率来瞄准通胀。降低利率鼓励借贷和投资，使 AD 右移；提高利率抑制支出。传导机制通过信贷、汇率和财富渠道发挥作用。
11. International Trade and Exchange Rates | 国际贸易与汇率
The theory of comparative advantage, developed by David Ricardo, demonstrates that countries gain from trade by specialising in goods where they have a lower opportunity cost, even if one country has an absolute advantage in all goods. Free trade increases global output and consumer choice, but can create structural unemployment in importing-competing industries.
大卫·李嘉图提出的比较优势理论证明，即使一国在所有商品上都具有绝对优势，各国仍可通过专门生产机会成本较低的商品而从贸易中获益。自由贸易提高全球产出和消费者选择，但可能造成进口竞争产业的失业。
Protectionist measures — tariffs, quotas, subsidies, and non-tariff barriers — shield domestic firms but often lead to higher consumer prices and inefficiency. Exchange rates, determined in foreign exchange markets by supply and demand, influence trade flows: a depreciation makes exports cheaper and imports dearer, improving the trade balance if the Marshall-Lerner condition holds.
保护主义措施——关税、配额、补贴及非关税壁垒——保护国内企业，但往往推高消费价格并降低效率。汇率由外汇市场供求决定，影响贸易流动：本币贬值使出口更便宜、进口更昂贵，若马歇尔-勒纳条件成立，则改善贸易差额。
12. Economic Development | 经济发展
Economic development differs from economic growth in that it encompasses improvements in living standards, health, education, and freedom. The Human Development Index (HDI) combines GNI per capita, life expectancy, and education indicators to rank countries. Developing economies often face barriers such as low savings, poor infrastructure, corruption, and institutional weakness.
经济发展有别于经济增长，它涵盖生活水平、健康、教育和自由的改善。人类发展指数（HDI）结合人均 GNI、预期寿命和教育指标对国家排名。发展中经济体常面临低储蓄、基础设施薄弱、腐败和制度软弱的障碍。
Policy strategies for development include investment in human capital, trade liberalisation, foreign direct investment, microfinance, and good governance. Sustainable development calls for balancing economic progress with environmental protection so that future generations’ well-being is not compromised.
促进发展的政策策略包括人力资本投资、贸易自由化、外国直接投资、小额信贷和良好治理。可持续发展要求在经济增长与环境保护间取得平衡，使后代的福祉不受损害。
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