外部性的分类及外部性理论的演化

The Classification of Externality and the Evolvement of Externality Theory

从产生外部影响和接受外部影响的主体的不同，外部性有两类典型的定义。从外部性的表现形式看，可以从七个角度进行分类。外部性理论发展经历了马歇尔的“外部经济”、庇古的“庇古税”和科斯的“科斯定理”三个阶段。这三个阶段被称之为外部性理论发展进程中的三块里程碑。张五常和杨小凯认为外部性概念是没有意义的。新兴古典经济学理论也许比外部性理论具有更强的解释力，但不一定能够彻底否定外部性理论。

There are two typical kinds of definition of externality based on the difference between subjects pro- ducing and receiving external effects. Externality can be classified from seven angles according to the forms of its expression. The development of externality theory has undergone three phases: Alfred Marshal's Exterior Economy, A. C. Pigou's Pigou Tax and R. Coase's Coase Therem. These three phases are known as three milestones in the development of eternality theory. Steven N. S. Cheung and Yang hold that the concept of ex- ternality is insignificant. New Classical Economics, which might have more elucidative power than externality theory, cannot necessarily deny externality theroy.