 A similar question arises with regard to the use of norms that have the character of standards rather than rules. (A rule is like a numerical speed limit, whereas a standard is like a norm that requires people to drive at a “reasonable” speed.) Legal systems use both types of norm (Sunstein 1994); they use standards for cases where the appropriate decision may vary with ambient circumstances and it seems better to trust the judgment of those who face a particular situation, rather than laying it down in advance. There is an element of respect for individuals’ powers of discernment conveyed in the use of a standard. At the same time standards allow for less certainty in the law, especially when it is difficult for the person attempting to comply with the norm to predict how his judgment will be viewed by an official or by a court. Hayek suggests that 