Conventional wisdom portrays contracts as static distillations of parties’ shared intent at some discrete point in time. In reality, however, contract terms evolve in response to their environments, including new laws, legal interpretations, and economic shocks. While several legal scholars have offered stylized accounts of this evolutionary process, we still lack a coherent, general theory that broadly captures the dynamics of real-world contracting practice. This paper advances such a theory, in which the evolution of contract terms is a byproduct of several key features, including efficiency concerns, information, and sequential learning by attorneys who negotiate several deals over time. Each of these factors contributes to the underlying evolutionary process, and their relative prominence bears directly on the speed, direction, and desirability of how contractual innovations diffuse. Using a formal model of bargaining in a sequence of similar transactions, we demonstrate how different evolutionary patterns can manifest over time, in both desirable and undesirable directions. We then take these insights to a real-world data set of over two thousand merger agreements negotiated over the last two decades, tracking the adoption of several contractual clauses, including pandemic-related terms, #MeToo provisions, Committee on Foreign Investment in the United States (CFIUS) conditions, and reverse termination fees. Our analysis suggests that there is not a one-size-fits-all paradigm for contractual evolution. Rather, the constituent forces affecting term evolution manifest in varying strengths across differing circumstances. We highlight several constructive applications of our framework, including how the study of contract negotiation unfolds when price cannot easily be adjusted and how to incorporate other forms of cognitive and behavioral biases into our general framework.

传统智慧将合同描述为各方在某个离散时间点的共同意图的静态蒸馏。然而，在现实中，合同条款会随着环境的变化而变化，包括新的法律、法律解释和经济冲击。虽然几位法律学者对这一演变过程提供了程式化的描述，但我们仍然缺乏一个连贯的、普遍的理论来广泛地捕捉现实世界承包实践的动态。本文提出了这样一种理论，其中合同条款的演变是几个关键特征的副产品，包括效率问题、信息和随着时间的推移谈判几笔交易的律师的顺序学习。这些因素中的每一个都有助于潜在的进化过程，它们的相对重要性直接关系到速度、方向、以及合同创新如何传播的可取性。在一系列类似交易中使用讨价还价的正式模型，我们展示了不同的进化模式如何随着时间的推移在合意和不合意的方向上表现出来。然后，我们将这些见解应用于过去二十年来谈判达成的两千多个合并协议的真实数据集，跟踪几个合同条款的采用情况，包括与大流行相关的条款、#MeToo 条款、美国外国投资委员会州 (CFIUS) 条件和反向终止费。我们的分析表明，合同演变没有一种万能的范式。相反，影响术语演变的构成力量在不同情况下表现出不同的强度。