The description of activities by the orderings employed in this chapter broadens the meaning of the term "externality," but at the same time it serves to tie together several of the loose ends that seem to have been left dangling in much of the discussion of this subject. The classical examples of external economies and diseconomies constitute only a small set of activities, and no one has discussed carefully the criteria for determining when an externality resulting from private behavior becomes sufficiently important to warrant a shift to the public sector. Few scholars in the field have called attention to the fact that much voluntary behavior is aimed specifically at removing external effects, notably the whole economic organization of activities in business enterprises. The limits to voluntary organization, and thus the pure laissez-faire model of social organization, are defined not by the range of significant externalities, but instead by the relative costs of voluntary and collective decision-making. If decision-making costs, as we have defined them, are absent, the pure laissez-faire model will be rationally chosen for all activities. All externalities, negative and positive, will be eliminated as a result of purely voluntary arrangements that will be readily negotiated among private people. Almost by definition, the presence of an externality suggests that "mutual gains from trade" can be secured from internalization, provided only that the decision-making costs do not arise to interfere with the reaching of voluntary agreements.