Many of the challenges to traditional definitions have to do with how to handle externalities, which pose fundamental economic policy problems when individuals, households, governments or firms do not include, in their total cost accounting, the indirect costs of or the benefits from their economic transactions. Private goods producers, for example, can lower their total costs, and therefore their prices, by externalizing (not including) certain costs, such as the costs of preventing air or water pollution that is a by-product of their production methods. Such a company, then, becomes a corporate free rider, driving up the cost of the "public goods" of clean air and water, which are often transnational resources.