Although externality is one of the basic concepts in economics, its rigorous definition remains elusive. This paper reconceptualizes externality as an instance of a broader phenomenon of incompatibility of plans—a situation where plans of different individuals cannot be materialized simultaneously because they compete for resources that are scarce. The plan incompatibility can be addressed by institutional arrangements involving mechanisms that determine which plans will be realized. Various institutional arrangements can be compared from the perspective of efficiency, operational costs, distributional effects, and other criteria. Regardless of the institutional arrangement, the spillover effects are unavoidable, as they are implied by scarcity. Therefore, the analysis of externalities should shift its focus from spillover effects to the mechanisms for allocating scarce resources among competing plans.

尽管外部性是经济学的基本概念之一，但其严格的定义仍然难以捉摸。本文将外部性重新概念化为更广泛的计划不相容现象的一个实例，即不同个人的计划由于争夺稀缺资源而无法同时实现的情况。计划的不兼容性可以通过涉及确定哪些计划将实现的机制的制度安排来解决。各种制度安排可以从效率、运行成本、分配效应等标准的角度进行比较。无论制度安排如何，溢出效应都是不可避免的，因为它们是由稀缺性所暗示的。因此，外部性分析应将重点从溢出效应转向竞争计划之间稀缺资源的配置机制。