Utility represents the satisfaction or well-being a consumer derives from consuming goods and services. Economists model consumer preferences using utility functions, which assign higher utility levels to preferred consumption bundles. Consumers are assumed to make choices that maximize their utility subject to their budget constraints, providing a foundation for understanding demand behavior.
Start with ordinal utility (ranking preferences) before moving to cardinal utility (assigning numerical values). Use examples like movie preferences or food choices to build intuition about trade-offs.
When you decide between two lunch options, you are implicitly ranking them: one is preferred, the other is not, or perhaps you are indifferent between them. Utility is the economist's name for this ordering—a number assigned to each option that respects your preferences by giving higher values to more preferred outcomes. Crucially, the numbers carry no absolute meaning. What matters is only the *ranking*: if you assign utility 10 to option A and utility 5 to option B, this does not mean A is twice as satisfying as B—it simply means A is preferred to B.
This is the distinction between ordinal and cardinal utility. Ordinal utility is like a race result (1st, 2nd, 3rd): it tells you the order but not the magnitude of the differences. Cardinal utility would assign meaningful magnitudes (A is exactly twice as good as B). Most modern consumer theory requires only ordinal utility: we need to know consumers can rank bundles consistently and prefer more to less, but we do not need to measure "utils" in any absolute sense, and we cannot compare utility across different people. If two utility functions produce the same ranking of every bundle, they represent identical preferences—only the ranking matters.
The utility function formalizes these preferences mathematically. If a consumer's preferences satisfy basic consistency assumptions (completeness—any two bundles can be compared; transitivity—if A is preferred to B and B to C, then A is preferred to C; monotonicity—more is better), they can be represented by a function U(X, Y) that assigns a utility level to each bundle (X, Y). A consumer allocating a limited budget behaves as if they are maximizing U(X, Y) subject to their income constraint. This optimization framework—maximize utility subject to a budget—is the foundation for everything in consumer theory that follows: indifference curves, the consumer's optimum, and the derivation of demand curves.
A key assumption built into this model is that preferences are stable. The consumer's underlying ranking does not change because prices or income change—what changes is which bundle is *affordable*, not which bundle is *preferred*. This stability is what makes the model predictive: fixed preferences plus changing constraints generate predictable, systematic changes in behavior. Without stable preferences, there would be no law of demand to derive and no basis for comparative analysis of policy changes.
This is a foundational topic with no prerequisites.
No prerequisites — this is a starting point.