Substitution for each other: two commodities that can be substituted for each other. Complementary commodities mean that there is a certain consumption dependence between the two commodities, that is, the consumption of one commodity must match that of another commodity.

The difference from the law of commodity operation lies in: substitution: if the price of commodity A rises, customers will seek to buy commodity B which is cheaper than commodity A and can bring similar satisfaction. Complementary product: the increase in the price of a complementary product of a commodity will lead to a decrease in demand for this commodity, because the demand for complementary products will decrease.