Definition of substitute goods 替代商品的定义 – Substitute goods are two alternative goods that could be used for the same purpose. 替代商品是指可以用于同一目的的两种替代商品。

Two phones – one Android (HTC) one iPhone (Apple). In one sense they are close substitutes but to some consumers entirely different. 两款手机--一款安卓（HTC），一款iPhone（苹果）。从某种意义上说，它们是接近的替代品，但对一些消费者来说是完全不同的。

• Substitutes present the consumer with alternative choices. 替代品为消费者提供了替代选择。
• If the price of one good increases, then demand for the substitute is likely to rise. 如果一种商品的价格上涨，那么对替代品的需求就有可能上升。
• Therefore, substitutes have a positive cross elasticity of demand. 因此，替代品具有正的交叉需求弹性。

Graph of two substitute goods 两种替代商品的图表

In the diagram on the left, there is a fall in the price of Android Phones causing consumers to demand more. (movement along the demand curve). 在左图中，安卓手机的价格下降导致消费者的需求增加。(沿着需求曲线的移动)。

• As a result, there is a fall in demand for the substitute (Apple iPhone) leading to less demand. 结果，对替代品（苹果iPhone）的需求下降，导致需求减少。

Cross elasticity of demand 需求的交叉弹性

Cross elasticity of demand (XED) measures the responsiveness of the demand for one good in relation to a change in the price of another. 需求的交叉弹性（XED）衡量一种商品的需求对另一种商品价格变化的反应能力。

For example, if the price of Android phones falls 10%, demand for the iPhone may fall 5%. 例如，如果安卓手机的价格下降10%，对iPhone的需求可能下降5%。

The XED of Android in relation to iPhone will be +0.5. 安卓手机相对于iPhone的XED将是+0.5。

Close Substitute Goods 紧密替代商品

• If two goods are close substitutes, there will be a high cross-elasticity of demand. 如果两种商品是紧密替代品，那么需求的交叉弹性就会很高。
• Example, if the price of Sainsbury’s flour increases 10%, demand for Hovis flour may increase by 20%. To consumers, there is little difference between the two goods. Therefore, the cross elasticity of demand is +2.0 例如，如果Sainsbury的面粉价格上涨10%，对Hovis面粉的需求可能会增加20%。对消费者来说，这两种商品之间没有什么区别。因此，需求的交叉弹性是+2.0。

Weak Substitute Goods 弱替代商品

• If goods are weak substitutes, there will be a low cross elasticity of demand. 如果商品是弱的替代品，需求的交叉弹性就会很低。
• Example, if the price of The Daily Mail increases 10%, the demand for the Financial Times may only increase by 1%. Therefore, the cross elasticity of demand is 0.1 . These two newspapers are weak substitutes. 例如，如果《每日邮报》的价格增加10%，对《金融时报》的需求可能只增加1%。因此，需求的交叉弹性为0.1。这两份报纸是弱替代物。
• If the price of margarine increases by 10%, demand for butter may rise 2%. XED = 0.2 如果人造黄油的价格上涨10%，对黄油的需求可能会上升2%。XED = 0.2

Perfect Substitutes 完全替代物

Two goods are perfect substitutes if the utility consumers get from one good is the same as another. For example a dollar from one FOREX 如果消费者从一种商品中获得的效用与另一种商品相同，那么这两种商品就是完全替代物。例如，来自一家外汇公司的一美元

• A dollar from one FOREX company is worth the same as getting a dollar from a different FOREX company. 从一家外汇公司获得的一美元与从另一家外汇公司获得的一美元价值相同。
• A4 paper from Office World gives the same utility as A4 paper from WHSmiths. 从 "办公室世界 "获得的A4纸与从WHSmiths获得的A4纸具有相同的效用。

Therefore, in theory, if one good was more expensive, there would be no demand as people would buy the cheaper alternative. 因此，在理论上，如果一种商品更贵，就不会有需求，因为人们会购买更便宜的替代品。