when are two goods said to be substitutes of each other
Substitute good A substitute goods is one goods that can be used instead of another. 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.
Inferior good In economics, an inferior good is a good whose demand decreases when consumer income rises (or demand rises when consumer income decreases),[1] unlike normal goods, for which the opposite is observed.[2] Normal goods are those for which demand rises as consumer income rises. [3] This would be the opposite of a superior good, one that is often associated with wealth and the wealthy, whereas an inferior good is associated with lower socio-economic groups.