MIT economist Jonathan Gruber opens his Principles of Microeconomics course by asking where consumer choices actually come from. This is lecture two of 14.01, and Gruber builds the foundation of consumer theory, starting with the axioms of consumer preferences, such as completeness and transitivity, that economists assume govern how people rank options. He then shows how these preference rankings get translated into a utility function, the mathematical tool used to represent what a consumer wants without claiming to measure happiness directly. Expect indifference curves sketched out and discussed as a visual counterpart to the utility function, along with the reasoning for why economists use ordinal rather than cardinal measures of satisfaction. The lecture is blackboard and marker, Gruber working through definitions and examples at a brisk pace, setting up the tools that the rest of the course will use to analyze demand.