📚 What is Economics? | 什么是经济学？
Economics is a social science that studies how individuals, firms and governments make choices when resources are limited. This opening chapter builds the foundation for the entire Cambridge A-Level Economics course by explaining the central economic problem of scarcity and the tools economists use to analyse choices.
经济学是一门社会科学，研究个人、企业和政府在资源有限时如何做出选择。本章为剑桥 A-Level 经济学课程奠定基础，解释稀缺性这一核心经济问题，以及经济学家用于分析选择的工具。
1. Scarcity and Choice | 稀缺与选择
Scarcity means that human wants are unlimited but the resources available to satisfy them are limited. Because scarcity is universal, every society must make choices about what to produce, how to produce and for whom to produce.
稀缺性意味着人类的欲望是无限的，但用于满足这些欲望的资源是有限的。由于稀缺性普遍存在，每个社会都必须就生产什么、如何生产和为谁生产做出选择。
Resources are scarce in relation to wants, not necessarily scarce in absolute terms. For example, clean water may be abundant in some regions but scarce in others, while time is scarce for everyone.
资源的稀缺是相对于欲望而言的，并非绝对数量稀少。例如，清洁水在某些地区可能充足，在其他地区却稀缺，而时间对每个人来说都是稀缺的。
A free good is available in unlimited supply and has no opportunity cost, such as air in most situations. An economic good is scarce and therefore commands a price.
免费物品是指供应无限且没有机会成本的物品，例如大多数情况下的空气。经济物品则是稀缺的，因此有价格。
2. Definition of Economics | 经济学的定义
Economics can be defined as the study of how to allocate scarce resources among competing uses to maximise welfare. It is a social science because it deals with human behaviour, which is often unpredictable and influenced by incentives.
经济学可以定义为研究如何在相互竞争的用途之间分配稀缺资源以实现福利最大化的学科。它是一门社会科学，因为它研究人类行为，而人类行为往往难以预测并受到激励的影响。
The subject is divided into two main branches: microeconomics and macroeconomics. Microeconomics focuses on individual markets and decision-makers, while macroeconomics examines the whole economy and aggregate variables.
经济学分为两大分支：微观经济学和宏观经济学。微观经济学关注单个市场和决策者，宏观经济学则研究整个经济体和总量变量。
Economists assume that individuals act rationally by comparing costs and benefits at the margin, but this does not mean people never make mistakes.
经济学家假设个人通过比较边际成本与边际收益来理性行事，但这并不意味着人们从不犯错。
3. Opportunity Cost | 机会成本
Opportunity cost is the value of the next best alternative forgone when a choice is made. It is a central concept because every decision involves a trade-off.
机会成本是指做出某种选择时所放弃的次优选择的价值。这是一个核心概念，因为每个决策都涉及权衡取舍。
For example, if a student spends one hour revising economics instead of working at a part-time job, the opportunity cost may be the wages lost during that hour. Money costs are only part of opportunity cost; time and other resources also matter.
例如，如果一名学生花一小时复习经济学而不是做兼职工作，机会成本可能是这一小时所损失的工资。货币成本只是机会成本的一部分，时间和其他资源也很重要。
Opportunity cost applies to individuals, firms and governments. A government that spends more on defence has fewer resources for healthcare or education.
机会成本适用于个人、企业和政府。政府在国防上支出更多，能用于医疗或教育的资源就会减少。
4. Factors of Production | 生产要素
Resources used to produce goods and services are called factors of production. They are traditionally classified into four groups: land, labour, capital and enterprise.
用于生产商品和服务的资源称为生产要素。传统上分为四类：土地、劳动、资本和企业家才能。
Land includes all natural resources such as soil, minerals, water and climate. Labour refers to human effort, both physical and mental, used in production.
土地包括所有自然资源，如土壤、矿产、水和气候。劳动是指生产中使用的体力和脑力劳动。
Capital consists of man-made goods used to produce other goods, such as machinery, tools and buildings. Enterprise is the ability to organise the other factors and take risks in pursuit of profit.
资本包括用于生产其他商品的人造物品，如机器、工具和建筑物。企业家才能是指组织其他生产要素并承担风险以追求利润的能力。
The reward for land is rent, for labour is wages, for capital is interest and for enterprise is profit.
土地的报酬是地租，劳动的报酬是工资，资本的报酬是利息，企业家才能的报酬是利润。
5. Production Possibility Curve | 生产可能性曲线
A production possibility curve (PPC) shows the maximum combinations of two goods that an economy can produce using all its resources efficiently. It illustrates scarcity, choice, opportunity cost and efficiency.
生产可能性曲线（PPC）显示一个经济体在使用全部资源并有效利用时，所能生产的两种商品的最大组合。它说明了稀缺性、选择、机会成本和效率。
Points on the curve are efficient; points inside the curve are inefficient because resources are unemployed or underemployed. Points outside the curve are unattainable with current resources and technology.
曲线上的点是有效率的；曲线内的点表示效率低下，因为资源未被充分使用或利用不足。曲线外的点在当前资源和技术条件下无法达到。
The slope of the PPC represents the marginal rate of transformation, which is the opportunity cost of producing one more unit of a good in terms of the other good forgone.
PPC 的斜率表示边际转换率，即多生产一单位某种商品所放弃的另一种商品的数量，也就是机会成本。
Economic growth shifts the PPC outward, allowing more of both goods to be produced. This can result from an increase in the quantity or quality of resources or from technological progress.
经济增长使 PPC 向外移动，从而可以生产更多两种商品。这可能是由于资源数量或质量的提高，或技术进步所致。
6. Positive and Normative Economics | 实证经济学与规范经济学
Positive statements are objective and testable claims about how the economy works. They can be supported or refuted by evidence, for example, “An increase in the money supply raises the price level.”
实证陈述是关于经济运行方式的客观且可检验的论断。它们可以通过证据来支持或反驳，例如 “货币供应量增加会提高物价水平”。
Normative statements involve value judgements about what ought to be. They cannot be tested by facts alone, for example, “The government should reduce income inequality.”
规范陈述涉及对应该怎样的价值判断。它们不能仅凭事实来检验，例如 “政府应该减少收入不平等”。
A-Level examinations often ask students to identify the difference. Remember that words such as ‘should’, ‘ought’ and ‘fair’ usually signal a normative statement.
A-Level 考试经常要求学生识别这种区别。请记住，诸如 “应该”、”应当” 和 “公平” 之类的词通常提示这是规范陈述。
Both types of statements are important. Positive analysis provides the factual basis, while normative analysis guides policy choices and debates.
两类陈述都很重要。实证分析提供事实基础，而规范分析指导政策选择和辩论。
7. Microeconomics and Macroeconomics | 微观经济学与宏观经济学
Microeconomics studies the behaviour of individual economic agents, such as households, firms and markets. Key topics include demand and supply, elasticity, market structures and market failure.
微观经济学研究单个经济主体的行为，如家庭、企业和市场。主要课题包括需求与供给、弹性、市场结构和市场失灵。
Macroeconomics looks at the economy as a whole. It examines aggregate output, unemployment, inflation, economic growth and international trade.
宏观经济学把经济作为一个整体来研究。它考察总产出、失业、通货膨胀、经济增长和国际贸易。
Although the two branches use different tools, they are closely linked. For instance, microeconomic decisions about consumption and investment add up to macroeconomic aggregates.
尽管这两个分支使用不同的工具，但它们紧密相连。例如，关于消费和投资的微观决策加总起来就构成了宏观经济总量。
In the Cambridge A-Level course, microeconomics and macroeconomics are often taught separately but students are expected to connect them in essay questions.
在剑桥 A-Level 课程中，微观经济学和宏观经济学通常分开教授，但学生需要在论文题中将二者联系起来。
8. Economic Agents and Their Objectives | 经济主体及其目标
The main economic agents are households, firms and governments. Each agent has different objectives and faces constraints from scarcity.
主要的经济主体是家庭、企业和政府。每个主体有不同的目标，并面临稀缺性带来的约束。
Households aim to maximise utility, or satisfaction, from the goods and services they consume, given their limited income.
家庭的目标是在收入有限的情况下，从所消费的商品和服务中获得最大的效用或满足感。
Firms aim to maximise profit, although in practice they may also pursue growth, market share or social responsibility. Governments aim to improve overall welfare, often through policies that correct market failures and redistribute income.
企业的目标是利润最大化，尽管在实践中它们也可能追求增长、市场份额或社会责任。政府的目标是提高整体福利，通常通过纠正市场失灵和再分配收入的政策来实现。
In economic models, we often simplify by assuming each agent is rational and self-interested, but real-world objectives can be more complex.
在经济模型中，我们通常简化假设每个主体是理性和自利的，但现实中的目标可能更为复杂。
9. Resource Allocation Mechanisms | 资源配置机制
Every economy must choose a mechanism to allocate scarce resources among competing uses. The three main systems are the market economy, the planned economy and the mixed economy.
每个经济体都必须选择一种机制，在相互竞争的用途之间分配稀缺资源。三种主要体制是市场经济、计划经济和混合经济。
In a market economy, resources are allocated through the price mechanism. Decisions are decentralised and driven by supply and demand. Prices act as signals, incentives and rationing devices.
在市场经济中，资源通过价格机制进行配置。决策是分散的，由供求驱动。价格起到信号、激励和配给的作用。
In a planned economy, the government makes most allocation decisions. It sets output targets, prices and wages. This may reduce inequality but often lacks efficiency and innovation.
在计划经济中，政府做出大部分配置决策。它设定产出目标、价格和工资。这可能减少不平等，但往往缺乏效率和创新。
Most real economies are mixed, combining market forces with government intervention to correct market failures, provide public goods and pursue equity.
大多数现实经济体都是混合经济，将市场力量与政府干预结合起来，以纠正市场失灵、提供公共物品并追求公平。
10. Economic Models, Ceteris Paribus and the Margin | 经济模型、其他条件不变与边际分析
Economists build simplified models to explain and predict behaviour. A model omits many details and focuses on key relationships between variables.
经济学家建立简化模型来解释和预测行为。模型省略许多细节，专注于变量之间的关键关系。
The ceteris paribus assumption means ‘other things being equal’. It allows economists to isolate the effect of one variable by holding others constant. For example, when examining the demand for a good, we hold income and tastes unchanged.
其他条件不变假设意味着 “其他条件相同”。它使经济学家能够通过保持其他变量不变来分离某个变量的影响。例如，在考察一种商品的需求时，我们保持收入和偏好不变。
Marginal analysis examines the effect of small changes, such as the additional benefit and additional cost of one more unit. Rational decision-makers compare marginal benefit with marginal cost.
边际分析
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