身边的经济学·社会常识英语30篇（2）

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无差异曲线展示权衡取舍，而不度量效用

An indifference curve connects all bundles of two goods that give a consumer exactly the same level of satisfaction.
Because utility cannot be measured directly, economists use relative rankings rather than numerical scores.
Each curve slopes downward, reflecting the fact that more of one good requires less of another to maintain equal preference.
The marginal rate of substitution (MRS) measures how much of good Y a person willingly gives up for one more unit of X.
MRS declines along the curve, showing diminishing willingness to trade as the consumer holds more of X.
Curves farther from the origin represent higher preference levels but never intersect each other logically.
Budget constraints determine which affordable bundle on the highest possible curve a consumer will choose.
This framework helps explain why people respond differently to price changes even with identical incomes.
It also clarifies why taxes on specific goods affect choices more than lump-sum taxes of equal value.
Though abstract, indifference curves underpin real-world policy analysis like food stamp design or carbon pricing.