「关键词」美国合同法重述，约因的充分性

　　§ 79. Adequacy Of Consideration； Mutuality Of Obligation

　　第79条。 约因的充分性；义务的均等性

　　If the requirement of consideration is met, there is no additional requirement of

　　在符合约因构成要件时，无需考虑下列额外要求：

　　（a） a gain, advantage, or benefit to the promisor or a loss, disadvantage, or detriment to the promisee； or

　　（a）（约因是否）给允诺人带来收益、优势或者利益；或者（约因是否）给相对人带来损失、劣势或者损害；或者

　　（b） equivalence in the values exchanged； or

　　（b）（双方当事人）所交换的价值（是否）相当；或者

　　（c） “mutuality of obligation.”

　　（c）（双方当事人的权利）义务（是否）均等。

　　Comment：

　　评论：

　　a. Rationale. In such typical bargains as the ordinary sale of goods each party gives up something of economic value, and the values exchanged are often roughly or exactly equivalent by standards independent of the particular bargain. Quite often promise is exchanged for promise, and the promised performances are sometimes divisible into matching parts. See § 31. Hence it has sometimes been said that consideration must consist of a “benefit to the promisor” or a “detriment to the promisee”； it has frequently been claimed that there was no consideration because the economic value given in exchange was much less than that of the promise or the promised performance； “mutuality of obligation” has been said to be essential to a contract. But experience has shown that these are not essential elements of a bargain or of an enforceable contract, and they are negated as requirements by the rules stated in §§ 71-78. This Section makes that negation explicit.

　　a.基本原理。在这样一个典型的普通货物买卖协商中，每一方当事人都放弃了一些经济价值，而且按照特定契约中的独立的标准，这些被交换的价值常常大致地或精确地相当。经常地，允诺换回另外的允诺，而允诺的履行在一些情况下则可分割为相匹配的几个部分。参见第31条。因此，约因有时会被认为必须由 “允诺人的利益”或者“受允诺人的损害”构成；经常会有这样的主张：因为所交换的经济价值要远远少于允诺或者被允诺的履行中的经济价值，所以约因并不存在：“义务的均等”被认为对一个契约而言具有必要性。但是经验表明，在一个协商或者可执行的契约中，这些并非必备要素，而且第71-78条所规定的规则也否认它们是构成要件。本部分明确了这一否认。