📚 Choice and Opportunity Cost | 选择与机会成本
In A-Level Economics, almost every decision can be traced back to one unavoidable fact: resources are scarce while human wants are unlimited. Choice and opportunity cost explain why individuals, firms and governments must rank alternatives and accept trade-offs. This article sets out the definition, measurement and diagrammatic treatment of opportunity cost for Cambridge International A-Level Economics.
在 A-Level 经济学中，几乎每一个决策都可以追溯到一个无法回避的事实：资源是稀缺的，而人类的欲望是无限的。选择与机会成本解释了为什么个人、企业和政府必须对备选方案进行排序并接受权衡。本文将为剑桥国际 A-Level 经济学阐述机会成本的定义、衡量方法以及图形分析。
1. Scarcity: The Root of Choice | 稀缺性：选择的根源
Scarcity means that the resources available to satisfy wants are limited. Economists classify resources into four factors of production: land, labour, capital and enterprise. Human wants, however, are virtually unlimited. This imbalance forces every economic agent to decide how to allocate resources among competing possible uses.
稀缺性意味着用于满足欲望的资源是有限的。经济学家将资源分为四种生产要素：土地、劳动、资本和企业家才能。然而，人类的欲望几乎是无限的。这种不平衡迫使每个经济主体决定如何在相互竞争的用途之间分配资源。
Because scarcity is permanent, choice is unavoidable. There is no economy, rich or poor, that can escape the need to choose. Even a billionaire cannot buy unlimited time or perfect health, so scarcity applies to time and attention as much as to money.
由于稀缺性是长期存在的，选择不可避免。没有一个经济体，无论贫富，能够逃避选择的需要。即使是亿万富翁也无法购买无限的时间或完美的健康，因此稀缺性适用于时间和注意力，正如它适用于金钱一样。
2. What Is Choice? | 什么是选择？
Choice is the act of selecting one option from a set of alternatives. In economics, choice is not random; it is assumed that agents compare the expected benefits and costs of available options and select the one that maximises their objective, such as utility for consumers or profit for firms.
选择是从一组备选方案中挑选一个选项的行为。在经济学中，选择不是随机的；通常假设经济主体会比较可选方案的预期收益和成本，并选择最能实现其目标的一项，例如消费者的效用最大化或企业的利润最大化。
Choice occurs at several levels. Consumers choose how to spend a limited budget. Workers choose between labour and leisure. Firms choose which goods or services to produce. Governments choose between spending tax revenue on healthcare, education, defence or infrastructure.
选择发生在多个层面。消费者选择如何支出有限的预算。劳动者在劳动与闲暇之间作出选择。企业选择生产哪些商品或服务。政府选择将税收用于医疗、教育、国防还是基础设施。
3. Defining Opportunity Cost | 机会成本的定义
Opportunity cost is the value of the next best alternative forgone when a choice is made. It is not the sum of all rejected alternatives, because only the most attractive alternative given up represents the true sacrifice. For example, if a student chooses to study economics, the opportunity cost is the best other use of that time, such as working part-time or studying another subject, whichever is valued highest.
机会成本是指作出选择时所放弃的次优替代选项的价值。它不是所有被拒绝选项的总和，因为只有所放弃的最有吸引力的那个选项才代表真正的牺牲。例如，如果一名学生选择学习经济学，机会成本就是该时间的最佳其他用途，例如兼职工作或学习另一门学科，取其中价值最高者。
Opportunity cost includes both explicit and implicit costs. Explicit costs are direct money payments, such as tuition fees. Implicit costs are non-monetary sacrifices, such as forgone wages or lost leisure time. A full economic cost calculation therefore captures more than accounting cost.
机会成本包括显性成本和隐性成本。显性成本是直接的货币支付，例如学费。隐性成本是非货币牺牲，例如放弃的工资或失去的闲暇时间。因此，完整的经济成本计算所包含的内容比会计成本更多。
Opportunity cost = value of next best alternative forgone
机会成本 = 所选方案放弃的次优方案价值
Economic cost = explicit cost + implicit cost
经济成本 = 显性成本 + 隐性成本
4. Opportunity Cost in Daily Decisions | 日常决策中的机会成本
Consider a student who has a free Saturday. She can revise for an economics test or work in a cafe for £40. If she revises, the opportunity cost is not simply £0; it is the £40 income and the work experience forgone. If she works, the opportunity cost is the higher test score and deeper understanding of economics that she might have achieved.
设想一名学生有一个空闲的周六。她可以复习经济学测验，也可以去咖啡馆工作赚取 40 英镑。如果她复习，机会成本并不是简单的 0 英镑；而是所放弃的 40 英镑收入和工作经验。如果她工作，机会成本就是本可获得的更高测验分数和对经济学更深入的理解。
Monetary examples are useful, but opportunity cost also applies to non-monetary resources. An hour spent scrolling on social media has an opportunity cost of an hour of sleep, exercise or study. Because time is scarce, every allocation of time involves a sacrifice.
货币例子很有用，但机会成本同样适用于非货币资源。花一小时浏览社交媒体的机会成本可能是一小时的睡眠、锻炼或学习。由于时间稀缺，每一次时间分配都涉及牺牲。
5. Free Goods and Economic Goods | 免费物品与经济物品
An economic good is scarce, so using it involves an opportunity cost. A free good is available in unlimited supply at zero price, so its use does not require sacrificing anything else. Pure examples include air and sunlight in most contexts. The distinction matters because not everything with a zero money price in the market is truly a free good.
经济物品是稀缺的，因此使用它包含机会成本。免费物品以零价格无限供应，因此使用它不需要牺牲其他任何东西。纯粹的例子包括大多数情况下的空气和阳光。这一区分很重要，因为市场上许多货币价格为零的东西并非真正的免费物品。
A school may provide free meals to students, but producing those meals uses scarce labour, ingredients and equipment. The meal is free to the individual student at the point of consumption, yet society still incurs an opportunity cost in supplying it. Economists therefore define ‘free’ carefully.
学校可能向学生提供免费餐，但生产这些餐食使用了稀缺的劳动、食材和设备。对于单个学生来说，这顿饭在消费时是免费的，但社会在供应它时仍付出机会成本。因此经济学家对“免费”的定义十分谨慎。
6. The Production Possibility Curve: Visualising Choice | 生产可能性曲线：可视化选择
A production possibility curve (PPC), also called a production possibility frontier, shows the maximum attainable combinations of two goods that an economy can produce using all available resources and current technology. It is a central diagram for illustrating scarcity, choice, efficiency and opportunity cost.
生产可能性曲线，也叫生产可能性边界，表示一个经济体在利用全部可用资源和现有技术时能够生产的两种商品的最大组合。它是说明稀缺性、选择、效率与机会成本的核心图形。
The table below shows a hypothetical economy producing only consumer goods and capital goods. Each point represents full employment of resources.
下表展示了一个只生产消费品和资本品的假设经济体。每一点都代表资源的充分利用。
| Combination | 组合 | Consumer goods (units) | 消费品（单位） | Capital goods (units) | 资本品（单位） |
|---|---|---|
| A | 0 | 40 |
| B | 5 | 30 |
| C | 10 | 20 |
| D | 15 | 更多咨询请联系16621398022（同微信）
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