本次讲座介绍了允诺禁反言原则，作为在缺乏传统约因的情况下，执行承诺的另一种依据。讲座以1898年的内布拉斯加州案例*Ricketts v. Scothorn*（里基茨诉斯科特霍恩案）为例，作为该原则的基础案例。在该案中，祖父向他的孙女凯蒂·斯科特霍恩承诺“按需”支付2000美元，年利率为6%，并告诉她不用再工作了。斯科特霍恩相信了这一承诺，辞去了工作。祖父后来去世，他的遗产管理人拒绝支付余下的欠款。 关键在于，这里没有议定的对价交换；祖父作出了赠与承诺，没有要求斯科特霍恩做任何回报。虽然她辞去了工作，但这并不是承诺的条件，由于缺乏约因，使得传统的合同执行变得不可能。然而，法院判决斯科特霍恩胜诉，认为如果允许遗产管理人违背承诺，在她依赖该承诺辞去工作而受到损害后，将是不公正的。 法院通过援引公平禁反言原则规避了约因要求。传统上，公平禁反言适用于对*事实*的陈述（例如，谎称自己是专家），并作为一种*盾牌*（一种抗辩），以防止某人否认先前断言的事实。在*Ricketts*案中，法院延伸了该原则，将其应用于*承诺*，并将其用作*利剑*，以创造一种新的诉讼理由。法院实际上“阻止”了遗产管理人辩称该承诺缺乏约因，因为斯科特霍恩已经依赖了该承诺。 讲座认为，这种对公平禁反言的延伸是一种“司法技巧”，即法院在意识到不公正的情况时，调整现有的法律概念来补救这种情况。这种创造性的破坏最终导致了一种独特的法律原则的形成。 塞缪尔·威利斯顿在他1920年关于合同法的论文中，以“允诺禁反言”的名称正式确定了这一概念。威利斯顿观察到，在像*Ricketts*这样的案件中，依赖似乎正在替代约因。然后，作为第一部《合同法重述》的报告人，他加入了第90条，该条文对该原则进行了编纂。现代的表述，见于第二部《合同法重述》： “如果承诺人应当合理预期该承诺会促使受诺人或第三方采取行动或不采取行动，并且该承诺确实促使了这种行动或不采取行动，那么只有在执行该承诺才能避免不公正的情况下，该承诺才具有约束力。对违约给予的补救措施可以根据正义的要求加以限制。” 这个定义突出了三个关键要素：（1）承诺人应该合理预期该承诺会促使依赖；（2）该承诺必须实际促使依赖；（3）只有执行该承诺才能避免不公正。 讲座进一步探讨了第90条的影响，特别关注补救措施。虽然*Ricketts*案中的法院判决斯科特霍恩获得票据的全部价值（期望损害赔偿，使她处于承诺得到履行时的状态），但第90条允许法院根据“正义的要求”限制补救措施。这可能意味着判决依赖损害赔偿，仅补偿受诺人因依赖该承诺而遭受的损失。在斯科特霍恩的案例中，这将相当于她辞去工作到找到新工作之前损失的工资，低于票据的总价值。 最后，讲座讨论了格兰特·吉尔摩的预测，即第90条将“吞噬”合同法。虽然允诺禁反言已经成为一个重要的原则，但它并没有取代传统的违约索赔。受诺人通常更喜欢起诉违约，因为它提供了更确定的责任基础，并避免了与允诺禁反言相关的“正义要求”和潜在的补救措施限制因素。最终，允诺禁反言提供了一张安全网，在缺乏传统约因但发生重大依赖的情况下，执行承诺，防止不公正的结果。

This lecture introduces the doctrine of promissory estoppel as an alternative basis for enforcing promises when traditional consideration is lacking. The lecture uses the 1898 Nebraska case, *Ricketts v. Scothorn*, as a foundational example. In *Ricketts*, a grandfather promised his granddaughter, Katie Scothorn, $2,000 "on demand" with 6% annual interest, telling her she wouldn't have to work anymore. Scothorn quit her job, relying on this promise. The grandfather later died, and his estate refused to pay the remaining balance of the note. The crucial point is that there was no bargained-for exchange; the grandfather made a gift promise, not requiring anything from Scothorn in return. While she quit her job, this wasn't a condition of the promise, making traditional contract enforcement impossible due to lack of consideration. The court, however, found for Scothorn, arguing that it would be unjust to allow the estate to renege on the promise after she had relied on it to her detriment by quitting her job. The court circumvented the consideration requirement by invoking the doctrine of equitable estoppel. Traditionally, equitable estoppel applies to representations of *facts* (e.g., falsely claiming to be a specialist) and serves as a *shield* (a defense) to prevent someone from denying a previously asserted fact. In *Ricketts*, the court stretched the doctrine, applying it to a *promise* and using it as a *sword* to create a new cause of action. The court essentially "stopped" the estate from arguing that the promise lacked consideration because Scothorn had relied on it. The lecture suggests that this stretching of equitable estoppel was a form of "judicial craft," where the court, recognizing an injustice, adapted an existing legal concept to remedy the situation. This creative destruction eventually led to the development of a distinct legal doctrine. Samuel Williston, in his 1920 treatise on contract law, formalized the concept under the name "promissory estoppel." Williston observed that in cases like *Ricketts*, reliance appeared to be acting as a substitute for consideration. He then, as the reporter on the first Restatement of Contracts, included Section 90, which codifies the doctrine. The modern formulation, found in the Second Restatement of Contracts, states: "A promise which the promisor should reasonably expect to induce action or forbearance on the part of the promisee or a third person and which does induce such action or forbearance is binding if injustice can be avoided only by enforcement of the promise. The remedy granted for breach may be limited as justice requires." This definition highlights three key elements: (1) the promisor should reasonably expect the promise to induce reliance; (2) the promise must actually induce reliance; and (3) injustice can be avoided only by enforcing the promise. The lecture further explores the implications of Section 90, specifically focusing on remedies. While the court in *Ricketts* awarded Scothorn the full value of the note (expectation damages, putting her in the position she would have been had the promise been fulfilled), Section 90 allows courts to limit the remedy "as justice requires." This could mean awarding reliance damages, compensating the promisee only for the losses incurred as a result of relying on the promise. In Scothorn's case, this would amount to the wages she lost from quitting her job before finding a new one, which was less than the total value of the note. Finally, the lecture addresses Grant Gilmore's prediction that Section 90 would "swallow" contract law. While promissory estoppel has become an important doctrine, it hasn't replaced traditional breach of contract claims. Promisees typically prefer to sue for breach of contract because it offers a more certain basis for liability and avoids the potentially limiting factors of "justice requires" and potential limitation of remedies associated with promissory estoppel. Ultimately, promissory estoppel provides a safety net, enforcing promises where traditional consideration is absent but significant reliance has occurred, preventing unjust outcomes.