外部性问题因为涉及到市场失灵、交易秩序、制度设计等前沿领域 ,从而成为经济学研究的重点领域之一。当私人成本与社会成本偏离的时候 ,直接的市场调整机制就会出现问题 ,市场经济需要自己的道德基础。科斯定理为我们提供了一个很好的参照系。 External problems are one of the key areas in economics because they involve the frontier fields such as market failure, transaction order and system design. When the private costs and social costs deviate from the direct market adjustment mechanism will be problems, the market economy needs its own moral basis. Coase theorem provides us with a good frame of reference.