双重合约论————基于对外部性的新解释

外部性的新定义是：没有参与订立特定相关合约的其他人所给予上述合约订立人的影响。上述订立的特定相关合约就是内部合约。所谓影响或某种控制，都是经过一致同意达成合约实现的。上述“其他人”不参加内部合约从而不受它控制，但对内部合约订立人产生影响，必定是同内部合约订立人达成了另外的合约即外部合约。上述内外合约组合成双重合约，这是一个普遍存在的事实。在拥有完全退出权的条件下，所有合约包括内外合约，都是每个参与人通过收益成本计算而一致同意达成的，其中包括为降低决策成本而一致同意采取各种授权方式达成的合约。内外合约的联系即相互之间的影响是双向的，其中外部合约作为外部选择点，由于条件的不同，或是可以保障内部合约的达成与稳定，或是可以替代内部合约参与人使其退出并改变内部合约。但上述退出权的实现取决于退出效用是否不小于退出成本。公共选择、合作博弈、讨价还价和一般均衡等理论同样可以解释双重合约。

The Theory of Dual Contract: On the Foundation of the New Explanation about Externality

Externality can be defined as the influence of other people not involved in the contract on the contractor. Such a contract is an internal contract. The influence or control is realized through a contract reached by way of consensus. The aforementioned ″other people″ are not under the control of the internal contract, but have influence on the internal contractor, which must be realized by reaching the external contract with the internal contractor. The internal contract and external contract form a dual contract, which is universal. Under the condition of full withdrawal right, all contracts, including the internal and external contracts, are reached with the consensus of every participant through profit and cost calculation, including the contract reached by way of mutually agreed authorization for the purpose of reducing decision-making cost. The external contract, as the external selection factor, due to varied conditions, may protect the completion and stability of the internal contract or replace the participants of the internal contract, enabling them to withdraw from the internal contract and change it. Realization of such a withdrawal right, however, depends on whether the withdrawal effect is bigger than the withdrawal cost. Theories like public choice, cooperative gambling, bargaining and general equilibrium can also be used to explain the dual contract.