----------------- HES POSTING ----------------- This two pillars (non-excludability and non-rivalry) approach is very common, but in teaching I lean harder on one pillar, non-rivalry. This is because public goods are generally thought of as a species of market failure. Not including cases of non-rivalry where we have excludability therefore seems to imply that the market provision is hunky-dory here. But if I manage to find a technology which allows excluding non-paying ships from the light of my lighthouse, so as to make it a profitable venture for me to produce it, it is still inefficient to charge above the marginal cost of zero. (Not to mention the deadweight nature of the costs of inventing such a technology!) It is especially important in this so-called "age of information" to make sure people understand the inefficiency of charging for the provision of non-rivalrous goods. Kevin Quinn ------------ FOOTER TO HES POSTING ------------ For information, send the message "info HES" to [log in to unmask]