Refer to carefully-labeled diagrams to explain each of the following:

a. Indifference curves are thin.







b. Indifference curves do not slope upward.







c. Indifference curves from the same family do not cross.







What will be an ideal response?

a. If indifference curves were thick, they would encompass bundles of goods that have more of both goods when compared to other bundles on the curve. In the figure above, the bundle with 5 units of good X and 6 units of good Y is on the same curve as the bundle with 6 units of good X and 7 units of good Y. Since consumers would prefer a bundle with more of both goods, they will not be indifferent towards the bundles. Therefore, such bundles cannot be on the same indifference curves, meaning that indifference curves are thin.
b. If indifference curves sloped upwards, it would be possible to move up the curve to bundles that contain more of both goods. Because of the "more-is-better" principle, consumers would prefer these bundles. Therefore, the consumer would not be indifferent to two bundles on the same curve.
c. According to the diagram, the consumer is indifferent between bundles A and B. The consumer is also indifferent between bundles B and C. This implies that the consumer should be indifferent between bundles A and C. But bundle C contains more of both goods and is therefore preferred to bundle A. Thus, crossing indifference curves lead to a contradiction.