A classic example of external benefits is the rescue of the person or property of strangers in high transaction cost settings. To illustrate, A sees a flowerpot about to fall on B's (a stranger's) head; if he shouts, B will be saved. A thus has in his power to confer a considerable benefit on B. The standard economic reaction to a situation in which there are substantial potential external benefits and high transaction costs is to propose legal intervention. In the example given, this would mean either giving A a right to a reward or punishing A if he fails to save B. Either method, we show, is costly and may result in misallocative effects. These objections to using the law to internalize the external benefits of rescue would be much less imposing were it not for altruism, a factor ignored in most discussion of externalities. Altruism may be an inexpensive substitute for costly legal methods of internalizing external benefits, though this depends on the degree of altruism, the costs of rescue, and the benefits to the rescuee. Although the general legal rule is not to reward the rescuer (nor to impose liability), the law recognizes the fragility of altruism and entitles the rescuer to a reward in certain instances. These include rewards to professional rescuers on land (normally a physician) and to rescuers at sea. In both instances the costs of rescue are likely to be sufficiently high to discourage rescue unless the rescuer anticipates compensation.
