Consider, for example, benefits provided by national defense or by measures to prevent air pollution. Exclusion would be impossible and moreover inefficient, since A’s partaking does not hurt B. Or take the case of a bridge which is not crowded, so A’s crossing will not interfere with that of B. Charging a toll would be quite feasible, but so long as the bridge is not heavily used, the charge would be inefficient since it would curtail use of the bridge, the marginal cost of which is zero. Or consider the case of a broadcast, which with the use of jamming can be made available only to those listeners who rent clearing devices. Again, the jamming would be inefficient since A’s reception does not interfere with B’s. Exclusion can be applied but should not be, because consumption is nonrival. Since the marginal cost to previous users of adding an additional consumer is zero, no admission price should be charged.