Why do people buy what they buy? Consumer theory provides a rigorous framework for understanding choice.
It begins with preferences. Economists assume consumers can rank bundles of goods — they prefer more to less, and their preferences are consistent. These assumptions let us draw indifference curves: lines connecting all the combinations of two goods that give a consumer the same level of satisfaction (utility). The shape of these curves reveals how willing a consumer is to trade one good for another.
The budget constraint shows what a consumer can actually afford. It is a straight line determined by income and prices. The consumer's problem is to find the best affordable bundle — the point where the highest indifference curve just touches the budget line. At this optimal point, the marginal rate of substitution (how much of one good the consumer is willing to give up for the other) equals the price ratio.
This is not just abstract theory. It explains why consumers buy different bundles when prices change, why subsidies and taxes alter behavior in predictable ways, and how income and substitution effects work together to shape demand curves.
Through interactive graphs, you will drag budget lines, explore indifference maps, and find optimal consumption points visually — building the geometric intuition that makes microeconomics click.