Suppose that an indifference curve slopes upward. If so, then the consumer could be indifferent between two bundles that lie on the same indifference curve, although one of the bundles would contain more of both consumption goods. Therefore, if an indifference curve has a hook, sloping upward, then that consumer's preferences will violate the assumption of more-is-better. Cannot form a hook because it then would be upward sloping.
