other names, including jointness of consumption and rivalness of consumption.13 All of these terms focus on the relationship that one person’s use has on the availability of resource units for others. One person’s harvest of fish, water, or timber subtracts from the amount left at any one time (and potentially, over time) for others. Because common-pool resources are subtractable, they can be easily congested, overharvested, degraded, and even destroyed. Many resources discussed in the theoretical literature on public goods are in fact common-pool resources because they have the attribute of subtractability, which classical public goods, such as world peace and scientific knowledge, do not have.
Some of the most challenging contemporary common-pool resource problems deal with the use of common-pool resources as sinks, which degrade through pollution. Common-pool sinks range in size from the global atmosphere, which is affected by the behavior of individuals in all countries of the world, to local watersheds and airsheds affected mainly by people at a single location. When a resource is a sink, the problem of overuse is putting too much of a contaminant into the resource as contrasted with the more familiar problem of taking too much out. Many watercourses suffer from both types of problems—too much water is extracted by each user, causing the costs of water for others to escalate, and too many pollutants are dumped into the resource, causing the quality of the water for others to decrease. Although the use of the common pool framework to understand sinks seems promising, this line of analysis is not as elaborate or as well studied as that examining resource extraction.
This problem was originally defined in its most extreme form—the impossibility of excluding beneficiaries once improvements to any set of resources had been made (Musgrave, 1959).14 If the nature of certain resources made it truly impossible to solve the exclusion problem, however, institutions could not have any role in managing those resources. The contemporary view is that resources vary in the cost of excluding potential beneficiaries from deriving benefits from them. If it is not practical to exclude a user nor possible to force that user to contribute to the costs of developing and maintaining the resource, the noncontributing user is called a free rider. The cost of excluding potential users is often a function of technology. Prior to the invention of barbed wire fences, it was very expensive to exclude potential users from rangelands, but with barbed wire, it became more feasible to exclude those who did not have entry rights.
Thus, a core problem related to the use of common-pool resources is the cost of preventing access by potential users unless they agree to abide by a set of rules. In regard to a common-pool resource, users free ride when they harvest from or dump pollutants into the resource independently and take only their own costs and benefits into account. One “solves” the free-rider problem when rules are adopted and accepted that regulate individual actions so that social benefits and