📚 Supply | 供给
Supply is a fundamental concept in economics that describes the behaviour of producers. It refers to the quantity of a good or service that firms are willing and able to offer for sale at various prices over a given time period. Understanding supply is essential for analysing how markets operate, as it interacts with demand to determine equilibrium price and quantity. In the Cambridge IGCSE Economics syllabus, you will learn about the law of supply, the supply curve, movements along and shifts of the curve, and the factors that influence supply decisions.
供给是经济学中描述生产者行为的一个基本概念。它指的是在一定时期内，企业愿意并能够以不同价格提供销售的商品或服务的数量。理解供给对于分析市场如何运作至关重要，因为它与需求相互作用，共同决定均衡价格和数量。在剑桥IGCSE经济学大纲中，你将学习供给定律、供给曲线、沿曲线的移动与曲线的平移，以及影响供给决策的各种因素。
1. What is Supply? | 什么是供给？
Supply is not simply about how much of a product is available in a shop. Economists define supply as the willingness and ability of producers to sell a product at a given price in a given time period. Both willingness and ability must be present. For example, a farmer may want to sell 1000 bags of rice, but if the farm can only harvest 600 bags, the actual supply is limited to 600. Effective supply therefore requires both the desire to sell and the resources to produce or distribute the goods.
供给并不仅仅指商店里有多少产品。经济学家将供给定义为生产者在特定时期内、以特定价格销售某种产品的意愿和能力。意愿和能力两者缺一不可。例如，一个农民可能想卖出1000袋大米，但如果农场只能收获600袋，那么实际供给只能限于600袋。因此，有效供给既需要销售的愿望，也需要生产或分销商品的资源。
2. The Law of Supply | 供给定律
The law of supply states that there is a direct (positive) relationship between price and quantity supplied, ceteris paribus. As the price of a good rises, the quantity supplied increases; as the price falls, the quantity supplied decreases. This happens because higher prices provide an incentive for producers to offer more for sale, since they can earn higher revenue and potentially higher profit. It also encourages new firms to enter the market or existing firms to expand production.
供给定律指出，在其他条件不变的情况下，价格与供给量之间存在直接（正相关）关系。当商品价格上升时，供给量增加；当价格下降时，供给量减少。这是因为较高的价格会激励生产者提供更多的产品用于销售，因为他们可以获得更高的收入和潜在的更高利润。这也会鼓励新企业进入市场，或者促使现有企业扩大生产规模。
3. The Supply Schedule and Supply Curve | 供给表与供给曲线
A supply schedule is a table that lists the quantity of a good that a producer is willing and able to supply at different prices. For example, a farmer might supply 100 kg of apples at $2 per kg, 150 kg at $3 per kg, and 200 kg at $4 per kg. When this data is plotted on a graph with price on the vertical axis and quantity on the horizontal axis, we obtain an upward-sloping supply curve. This curve visually represents the law of supply.
供给表是一个表格，列出了生产者在不同价格下愿意并能够提供的商品数量。例如，一个农民可能在每公斤2美元的价格下供应100公斤苹果，在每公斤3美元时供应150公斤，在每公斤4美元时供应200公斤。将这些数据绘制在价格位于纵轴、数量位于横轴的图形上，我们就得到一条向上倾斜的供给曲线。这条曲线直观地展示了供给定律。
4. Individual vs Market Supply | 个别供给与市场供给
Individual supply refers to the supply of a single producer at each price level. Market supply, on the other hand, is the sum of all individual supplies in the market at each given price. It is obtained by horizontally summing the individual supply curves. Market supply is usually more relevant for analysing real-world markets, as it captures the total output that all firms are prepared to offer for sale. The market supply curve also slopes upwards, reflecting the law of supply.
个别供给指的是单个生产者在每个价格水平下的供给量。而市场供给则是市场中所有个别供给在每个给定价格下的总和，它是通过对个别供给曲线进行水平加总得到的。市场供给通常更适合于分析现实世界中的市场，因为它反映了所有企业准备出售的总产出。市场供给曲线同样向上倾斜，反映了供给定律。
5. Movements Along the Supply Curve: Extension and Contraction | 沿供给曲线的移动：扩张与收缩
A change in price, ceteris paribus, leads to a movement along the existing supply curve. If the price increases, the quantity supplied expands, and this is called an extension of supply. If the price decreases, the quantity supplied contracts, known as a contraction of supply. In both cases, the supply curve itself does not shift. For instance, if the market price of coffee rises from $5 to $7 per bag, coffee growers move up along the supply curve and offer more bags for sale. This is an extension, not an increase in supply.
在其他条件不变的情况下，价格的变化会导致沿原有供给曲线的移动。如果价格上升，供给量增加，这被称为供给的扩张。如果价格下降，供给量减少，则称为供给的收缩。在这两种情况下，供给曲线本身并没有发生位移。例如，如果咖啡的市场价格从每袋5美元上升到7美元，咖啡种植者会沿着供给曲线向上移动，并提供更多的咖啡袋出售。这是供给的扩张，而不是供给的增加。
6. Shifts in Supply: Increase and Decrease | 供给曲线的移动：增加与减少
When factors other than the price of the good itself change, the entire supply curve shifts. An increase in supply means that at every given price, producers are willing to supply more of the good. This is represented by a rightward shift of the supply curve. A decrease in supply means that at every price, producers are willing to supply less, causing a leftward shift. Such shifts can result from changes in costs of production, technology, government policies, or other external factors. It is crucial to distinguish between a movement along the curve (caused by price change) and a shift of the curve (caused by non-price determinants).
当商品本身价格以外的因素发生变化时，整条供给曲线会发生位移。供给的增加意味着在每一个既定价格下，生产者都愿意提供更多的商品。这表现为供给曲线向右移动。供给的减少则意味着在每一个价格下生产者愿意提供的商品变少，导致曲线向左移动。这类位移可能是由生产成本、技术、政府政策或其他外部因素的变化引起的。区分沿曲线的移动（由价格变化引起）与曲线的位移（由非价格决定因素引起）至关重要。
7. Factors Causing an Increase in Supply (Rightward Shift) | 导致供给增加的因素（向右移动）
Several determinants can shift the supply curve to the right. An improvement in technology can lower production costs, enabling firms to produce more at each price. A fall in the costs of inputs, such as raw materials or labour, also increases supply. Government subsidies to producers effectively reduce their costs and encourage higher output. Favourable weather conditions can boost agricultural harvests, shifting the supply curve rightward. Additionally, a rise in the number of sellers in the market increases market supply.
若干决定因素可以使供给曲线向右移动。技术进步可以降低生产成本，使企业在每个价格下都能生产更多产品。原材料或劳动力等投入品成本的下降也会增加供给。政府对生产者的补贴有效降低了他们的成本，并鼓励更高的产出。有利的天气条件可以促进农业丰收，使供给曲线向右移动。此外，市场中卖方数量的增加也会增加市场供给。
8. Factors Causing a Decrease in Supply (Leftward Shift) | 导致供给减少的因素（向左移动）
Conversely, an increase in production costs, such as higher wages or more expensive electricity, reduces supply because production becomes less profitable. The imposition of an indirect tax, like a customs duty on imported components, raises costs and shifts supply leftwards. Bad weather, natural disasters, or crop diseases can destroy output and sharply reduce agricultural supply. A decrease in the number of firms in the industry, perhaps due to bankruptcies or strict regulations, also contracts supply. Furthermore, producers' expectations of a future price rise may cause them to reduce current supply in order to sell later at higher prices.
相反地，生产成本的上升，如工资上涨或电价变贵，会减少供给，因为生产变得不那么有利可图。征收间接税，比如对进口零部件征收关税，会提高成本，使供给向左移动。恶劣天气、自然灾害或作物病害可能破坏产出，急剧减少农业供给。行业中企业数量的减少，或许是由于破产或严格管制，也会使供给收缩。此外，生产者对未来价格上涨的预期可能导致他们减少当前的供给，以便在未来以更高的价格出售。
9. The Role of Price Elasticity of Supply (PES) | 供给的价格弹性
Price elasticity of supply measures the responsiveness of quantity supplied to a change in price. It is calculated by the formula:
供给的价格弹性衡量供给量对价格变化的反应程度。它的计算公式为：
PES = (% change in quantity supplied) ÷ (% change in price)
If PES is greater than 1, supply is elastic, meaning producers can quickly adjust output when prices change. If PES is less than 1, supply is inelastic, indicating that it is difficult for producers to change quantity supplied in the short run. Goods that are quick to produce, like manufactured items, tend to have elastic supply, while agricultural products or those with long production lags often have inelastic supply. Understanding PES helps explain why price fluctuations in some markets are more extreme than in others.
如果PES大于1，供给就是富有弹性的，意味着生产者可以迅速调整产出以应对价格变化。如果PES小于1，供给就是缺乏弹性的，表明生产者在短期内难以改变供给量。生产周期短的商品，如制成品，往往具有弹性供给，而农产品或生产周期长的产品通常缺乏供给弹性。理解供给价格弹性有助于解释为什么某些市场的价格波动比其他市场更为剧烈。
10. Impact of Government Intervention: Taxes and Subsidies | 政府干预的影响：税收与补贴
Government policies can significantly shift the supply curve. An indirect tax, such as a specific tax or ad valorem tax, raises the cost of production. This shifts the supply curve to the left (a decrease in supply). The vertical distance between the original and new supply curves represents the amount of the tax. As a result, market price for consumers rises and quantity falls. In contrast, a subsidy to producers lowers their costs and shifts the supply curve to the right (an increase in supply). This leads to a lower equilibrium price and higher output, benefiting consumers but costing the government revenue.
政府政策可以显著改变供给曲线。间接税，如从量税或从价税，会提高生产成本。这使得供给曲线向左移动（供给减少）。原供给曲线与新供给曲线之间的垂直距离代表了税金的数额。结果是，消费者面对的市场价格上升，交易量下降。相反，对生产者的补贴会降低他们的成本，使供给曲线向右移动（供给增加）。这导致均衡价格下降，产出增加，使消费者受益，但增加了政府的财政支出。
11. Summary Table of Determinants | 决定因素总结表
| Determinant | Effect on Supply Curve | Shift Direction |
|---|---|---|
| Falling input costs | Increase in supply | Rightward |
| Improved technology | Increase in supply | Rightward |
| Government subsidy | Increase in supply | Rightward |
| Good weather | Increase in supply | Rightward |
| More sellers | Increase in supply | Rightward |
| Rising input costs | Decrease in supply | Leftward |
| Indirect tax | Decrease in supply | Leftward |
| Bad weather / disaster | Decrease in supply | Leftward |
| Fewer sellers | Decrease in supply | Leftward |
The table above categorises the main determinants of supply and how they affect market supply. Remember that any change that lowers production costs or makes production easier will increase supply, while any change that raises costs or disrupts production will decrease supply. In the IGCSE exam, you should be able to identify these factors from given scenarios and predict the resulting shift of the supply curve.
上表归纳了主要的供给决定因素以及它们如何影响市场供给。请记住，任何降低生产成本或使生产更容易的变化都会增加供给，而任何提高成本或干扰生产的变化都会减少供给。在IGCSE考试中，你应该能够根据给定情景识别这些因素，并预测供给曲线由此产生的移动方向。
12. Real-World Example | 现实案例
Consider the global market for smartphones. When a major manufacturer invests in automated assembly lines, this technological advancement reduces the cost of producing each phone. At the same time, the price of lithium for batteries might increase, raising input costs. The net effect on supply depends on the relative strengths of these forces. If the government also imposes a tariff on imported microchips, supply could decrease despite the technological improvement. Analysing real markets requires weighing multiple determinants simultaneously. IGCSE exam questions often present such scenarios and ask you to explain the likely shifts, so practising with case studies is highly recommended.
以全球智能手机市场为例。当一家大型制造商投资于自动化装配线时，这种技术进步会降低每部手机的生产成本。与此同时，电池用锂的价格可能上升，从而提高投入成本。供给的净效应取决于这些力量的相对强度。如果政府还对进口微芯片征收关税，那么即便存在技术进步，供给仍可能减少。分析真实的市场需要同时权衡多种决定因素。IGCSE考试的题目常常给出这类情景并要求你解释可能发生的曲线移动，因此强烈建议通过案例分析进行练习。
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