In microeconomic theory, the demand curve for a good can be derived from indifference curve analysis by examining consumer equilibrium under different price levels. The indifference curve approach is based on the assumptions that consumers are rational, aim to maximize satisfaction, and face budget constraints. To derive the demand curve for an inferior good, we must analyze how quantity demanded changes when the price of the good changes, keeping income constant. An inferior good is one for which demand decreases when consumer income increases. However, this does not imply that the demand curve of an inferior good is upward sloping. The demand curve is still generally downward sloping because the substitution effect usually dominates the income effect. To derive the demand curve, consider a consumer who purchases an inferior good along with other commodities. Initially, the consumer is in equilibrium where the budget line is tangent