Tractable consumer choice

We present a rational model of consumer choice, which can also serve as a behavioral model. The central construct is lambda, the marginal utility of money, derived from the consumer's rest-of-life problem. It provides a simple criterion for choosing a consumption bundle in a separable consumption problem. We derive a robust approximation of lambda and show how to incorporate liquidity constraints, indivisibilities, and adaptation to a changing environment. We find connections with numerous historical and recent constructs, both behavioral and neoclassical, and draw contrasts with standard partial equilibrium analysis. The result is a better grounded, more flexible, and more intuitive description of consumer choice.