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A Pigovian tax (also spelled Pigouvian tax) is a tax applied to a market activity that is generating negative externalities (costs for someone other than the person on whom the tax is imposed). The tax is intended to correct an inefficient market outcome, and does so by being set equal to the social cost of the negative externalities. In the presence of negative externalities, the social cost of a market activity is not covered by the private cost of the activity. In such a case, the market outcome is not efficient and may lead to over-consumption of the product.〔Sandmo, Agnar (2008). "Pigouvian taxes," ''The New Palgrave Dictionary of Economics'', 2nd Edition. ( Abstract. )〕 An often-cited example of such an externality is environmental pollution.〔.〕 In the presence of positive externalities, i.e., public benefits from a market activity, those who receive the benefit do not pay for it and the market may under-supply the product. Similar logic suggests the creation of a Pigovian subsidy to make the users pay for the extra benefit and spur more production.〔Turvey, Ralph (1963). "On Divergences between Social Cost and Private Cost," Economica'', N.S., 30(119), pp. (309 )-313.〕 An example sometimes cited is a subsidy for provision of flu vaccine.〔• Carlton, Dennis W., and Glenn C. Loury (1980). "The Limitations of Pigouvian Taxes as a Long-Run Remedy for Externalities," ''Quarterly Journal of Economics'', 95(3), pp. (559 )-566. • Althouse, Benjamin M., Theodore C. Bergstrom, and Carl T. Bergstrom (2010). "A Public Choice Framework for Controlling Transmissible and Evolving Diseases," ''Proceedings of the National Academy of Sciences'',January 26; 107(suppl. 1), pp. (1696–1701. )〕 Pigovian taxes are named after economist Arthur Pigou who also developed the concept of economic externalities. William Baumol was instrumental in framing Pigou's work in modern economics.〔 ==Pigou's original argument== In 1920, British economist Arthur C. Pigou wrote ''The Economics of Welfare''. In it, Pigou argues that industrialists seek their own marginal private interest. When the marginal social interest diverges from the marginal private interest, the industrialist has no incentive to internalize the cost of the marginal social cost. On the flip side, Pigou argues, if an industry produces a marginal social benefit, the individuals receiving the benefit have no incentive to pay for that service. Pigou refers to these situations as incidental uncharged disservices and incidental uncharged services, respectively. Pigou provides numerous illustrations of incidental uncharged disservices. For example, if a contractor builds a factory in the middle of a crowded neighborhood, the factory causes these incidental uncharged disservices: higher congestion, loss of light, and a loss of health for the neighbors. He also references businesses that sell alcohol. The sale of alcohol necessitates higher costs in policemen and prisons, Pigou argues, because of the crime associated with alcohol. In other words, the net private product of alcohol businesses is peculiarly large relative to the net social product of the same business. He suggests that this is why most countries tax alcohol businesses. The divergence between the marginal private interest and the marginal social interest produces two primary results. First, as already noted, the party receiving the social benefit does not pay for it, and the one creating the social harm does not pay for it. Second, when the marginal social cost exceeds the private marginal benefit, the cost-creator over-produces the product. Ultimately, because non-pecuniary externalities overestimate the social value, they are over-produced. To deal with over-production, Pigou recommends a tax placed on the offending producer. If the government can accurately gauge the social cost, the tax could equalize the marginal private cost and the marginal social cost. In more specific terms, the producer would have to pay for the non-pecuniary externality that it created. This would effectively reduce the quantity of the product produced, moving the economy back to a healthy equilibrium. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pigovian tax」の詳細全文を読む スポンサード リンク
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