budget constraints

The primary constraints are scope, time, quality and budget.

They are limited by a budget constraint.

Indifference curve: series of curve reflecting the preference structure of the individual.

Budget constraint: the material resource constraint the individual faces in choices.

The demand curve, being inherently designated as rational, seeks to maximise utility. Thus, in a Walrasian equilibrium, the consumer construct his demand curve at the points where his contract curve equals to his budget constraint (or, in mathematical terms, when the constraint and optimal indifferences are tangent to one another). These tangencies construct a curve which is the individual's demand function.

It is the equilibrium point of utility maximization.