📚 Meaning of the Term Ceteris Paribus | 其他条件不变的含义
In A-Level Economics, the Latin term ceteris paribus is one of the first analytical tools students encounter. It translates as "other things being equal" or "all other things held constant". The phrase is used to isolate the relationship between two variables by assuming that all other relevant influences remain unchanged. Without this simplifying assumption, it would be extremely difficult to explain how a change in price affects quantity demanded, or how a change in income affects consumption.
在 A-Level 经济学中，拉丁语 ceteris paribus 是学生最早接触的分析工具之一，可译为“其他条件相同”或“其他因素保持不变”。这一短语用于隔离两个变量之间的关系，假设所有其他相关影响因素均不发生变化。如果没有这一简化假设，就很难解释价格变化如何影响需求量，或收入变化如何影响消费。
1. Defining Ceteris Paribus | 定义其他条件不变
Ceteris paribus is a Latin phrase meaning "other things being equal". In economics, it is used as a modelling assumption: when analysing the effect of one variable on another, we hold all other variables constant. For example, the law of demand states that a rise in price reduces quantity demanded, ceteris paribus. This means the prediction only holds if income, tastes, the prices of substitutes and complements, and other influences are unchanged.
Ceteris paribus 是一个拉丁语短语，意为“其他条件相同”。在经济学中，它被用作一种建模假设：在分析一个变量对另一个变量的影响时，我们保持所有其他变量不变。例如，需求定律指出，在其他条件不变的情况下，价格上升会减少需求量。这意味着只有在收入、偏好、替代品和互补品价格以及其他影响因素都不变时，这一预测才成立。
Equivalent expressions are often used in textbooks and exam questions. They all carry the same logical meaning and can be used interchangeably when constructing economic arguments.
教科书和考试题中经常使用同义表达。它们在构建经济学论证时具有相同的逻辑含义，可以互换使用。
Other things being equal — 其他条件相同
All else held constant — 其他所有因素保持不变
Holding other factors unchanged — 保持其他因素不变
Assuming no other changes occur — 假设没有其他变化发生
2. Why Economists Use Ceteris Paribus | 经济学家为何使用这一假设
Real-world economies are complex, with many variables changing at the same time. If economists tried to study all variables simultaneously, they would struggle to identify clear cause-and-effect relationships. Ceteris paribus allows them to focus on one change at a time, making theories testable and diagrams easier to construct. It turns a messy reality into a manageable model.
现实经济非常复杂，许多变量会同时发生变化。如果经济学家试图同时研究所有变量，就难以识别清晰的因果关系。Ceteris paribus 使他们能够一次只关注一个变化，从而使理论可检验、图形更容易构建。这一假设将纷繁复杂的现实转化为易于处理的模型。
It is especially important when using two-dimensional diagrams. A demand curve, for instance, only shows the relationship between price and quantity demanded. All other determinants of demand are held constant so that the curve can be drawn on a single graph. If any of those determinants changes, the entire curve shifts.
在使用二维图形时，这一点尤为重要。例如，需求曲线只显示价格与需求量之间的关系。需求的所有其他决定因素都被保持不变，以便曲线能够绘制在单一图形上。如果其中任何一个决定因素发生变化，整条曲线就会发生平移。
3. Ceteris Paribus in Demand Analysis | 需求分析中的应用
The law of demand is usually expressed with an explicit ceteris paribus assumption. When the price of a good rises, consumers reduce the quantity demanded because the opportunity cost of buying it increases. This negative relationship is written as:
需求定律通常伴随着明确的“其他条件不变”假设。当一种商品的价格上升时，消费者会减少需求量，因为购买该商品的机会成本上升。这种负相关关系可以写成：
P↑ → Qd↓, ceteris paribus
However, the law of demand only holds if other determinants of demand, such as income, preferences, the prices of related goods, population size, and expectations, do not change. If income rises at the same time as price, a consumer might actually buy more of the good despite the price increase. That does not disprove the law of demand; it simply means ceteris paribus was violated.
然而，需求定律只有在收入、偏好、相关商品价格、人口规模和预期等其他需求决定因素不变时才成立。如果收入与价格同时上升，消费者可能尽管价格上升仍购买更多该商品。这并不推翻需求定律，只是说明“其他条件不变”的前提被破坏了。
When applying the law of demand in an exam, you should list the key non-price determinants of demand and state that they are assumed unchanged. Common determinants include:
在考试中应用需求定律时，你应该列出需求的主要非价格决定因素，并说明假设它们不变。常见的决定因素包括：
Income — 收入
Tastes and preferences — 偏好
Prices of substitutes and complements — 替代品和互补品价格
Population and demographics — 人口与人口结构
Expectations of future prices — 对未来价格的预期
4. Ceteris Paribus in Supply Analysis | 供给分析中的应用
The law of supply similarly depends on ceteris paribus. As the price of a good rises, producers are more willing and able to supply it because higher prices increase potential profit. This positive relationship is summarised as:
供给定律同样依赖“其他条件不变”的假设。当商品价格上升时，生产者更愿意且更有能力供给该商品，因为更高的价格增加了潜在利润。这种正相关关系可以概括为：
P↑ → Qs↑, ceteris paribus
The assumption holds only when costs of production, technology, taxes, subsidies, the number of sellers, weather conditions, and other supply-side factors are unchanged. A rise in wages or energy costs would shift the supply curve left even if the product price is rising.
只有在生产成本、技术、税收、补贴、卖方数量、天气条件和其他供给侧因素不变时，这一假设才成立。工资或能源成本上升会使供给曲线向左平移，即使产品价格正在上升。
Students often forget that changes in technology or indirect taxes are non-price supply factors. If technology improves, supply increases at every price, so the supply curve shifts right. This shift is not caused by a change in the product's own price, and therefore it violates the ceteris paribus assumption behind the law of supply.
学生常忘记技术或间接税的变化属于非价格供给因素。如果技术改进，在任何价格水平下供给都会增加，因此供给曲线向右平移。这种平移并非由产品自身价格变化引起，因而违反了供给定律背后的“其他条件不变”假设。
5. Movements Along vs Shifts of Curves | 沿曲线移动与曲线平移的区别
Ceteris paribus helps students distinguish between a movement along a curve and a shift of the curve. A change in the good's own price causes a movement along the demand or supply curve, because price is already shown on the vertical axis and quantity on the horizontal axis. All other factors are held constant.
Ceteris paribus 有助于学生区分沿曲线移动与曲线平移。商品自身价格的变化会导致沿需求曲线或供给曲线移动，因为价格已显示在纵轴上，数量显示在横轴上。所有其他因素保持不变。
By contrast, a change in any non-price determinant — such as income for demand or production costs for supply — violates the ceteris paribus assumption. The entire curve shifts to the left or right. This distinction is a common source of exam questions.
相比之下，任何非价格决定因素的变化——例如需求的收入或供给的生产成本——都违反了“其他条件不变”的假设。整条曲线向左或向右平移。这一区分是考试中的常见考点。
| Change | Effect on diagram | Ceteris paribus status |
|---|---|---|
| Own price of the good | Movement along curve | Held |
| Consumer income | Published by TutorHao | A-Level Economics Revision Series | aleveler.com
