Substitute good

In consumer theory, substitute goods or substitutes are products that a consumer perceives as similar or comparable, so that having more of one product makes them desire less of the other product. Formally, X and Y are substitutes if, when the price of X rises, the demand for Y rises.

Potatoes from different farms are an example: if the price of one farm's potatoes goes up, then it can be presumed that fewer people will buy potatoes from that farm and source them from another farm instead.

There are different degrees of substitutability. For example, a car and a bicycle may substitute to some extent: if the price of motor fuel increases considerably, one may expect that some people will switch to bicycles.

In economics, one way that two or more goods can be classified is by examining the relationship of the demand schedules when the price of one good changes. This relationship between demand schedules leads to classification of goods as either substitutes or complements. Substitute goods are goods which, as a result of changed conditions, may replace each other in use (or consumption). A substitute good, in contrast to a complementary good, is a good with a positive cross elasticity of demand. This means a good's demand is increased when the price of another good is increased. Conversely, the demand for a good is decreased when the price of another good is decreased. If goods A and B are substitutes, an increase in the price of A will result in a leftward movement along the demand curve of A and cause the demand curve for B to shift out. A decrease in the price of A will result in a rightward movement along the demand curve of A and cause the demand curve for B to shift in.

Examples of substitute goods include margarine and butter, tea and coffee. Substitute goods not only occur on the consumer side of the market but also the producer side. Substitutable producer goods would include: petroleum and natural gas (used for heating or electricity). The degree to which a good has a perfect substitute depends on how specifically the good is defined. Take for example, the demand for Rice Krispies cereal, which is a very narrowly defined good as compared to the demand for cereal generally. The fact that one good is substitutable for another has immediate economic consequences: insofar as one good can be substituted for another, the demands for the two kinds of good will be interrelated by the fact that customers can trade off one good for the other if it becomes advantageous to do so.

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Wikipedia