Society's decision to regulate just these activities is not ad hoc. The decision to restrict admission to certain vocations and to forbid some people from driving is based on an eminently plausible, though not often explicitly formulated, rationale.(1) We require drivers to be licensed because driving an auto is an activity which is potentially harmful to others, safe performance of the activity requires a certain competence, and we have a moderately reliable procedure for determining that competence. The potential harm is obvious: incompetent drivers can and do maim and kill people. The best way we have of limiting this harm without sacrificing the benefits of automobile travel is to require that all drivers demonstrate at least minimal competence. We likewise license doctors,. lawyers, and psychologists because they perform activities which can harm others. Obviously they must be proficient if they are to perform these activities properly, and we have moderately reliable procedures for determining proficiency Imagine a world in which everyone could legally drive a car, in which everyone could legally perform surgery, prescribe medications, dispense drugs. or offer legal advice. Such a world would hardly be desirable.