L’imprévision est un thème à la frontière entre liberté contractuelle et justice contractuelle. Cependant, un nouveau regard peut être porté sur cette institution du droit des contrats grâce à la théorie des contrats relationnels développée par Ian R. Macneil ou encore à travers le contrat-coopération théorisé par Suzanne Lequette. Ces théories invitent à prendre en considération la valeur intrinsèque du lien contractuel et l’incomplétude du contrat. L’imprévision fait donc partie intégrante des contrats relationnels de par leur nature. La vocation première des contrats relationnels est de perdurer, obligeant les contractants à des normes de coopération et de flexibilité. Sous couvert de bonne foi, la relationnalité serait le fondement des changements de circonstances. Une étude comparative du régime des changements de circonstances apporte certaines précisions. Il semble exister deux approches des changements de circonstances, l’une restreinte aux modifications économiques et l’autre étendue, basée sur l’objectif ou le fondement contractuel. Une approche étendue de l’imprévision semble nécessaire dans les contrats relationnels. Enfin, les effets des changements de circonstances devraient donner priorité au maintien de la relation et à la norme de coopération en imposant une renégociation puis en permettant une adaptation judiciaire des termes de l’engagement. La résiliation, contraire à la nature des contrats relationnels, ne devrait intervenir qu’exceptionnellement. / Hardship is a topic at the border between contractual freedom and contractual justice. However, a new glance can be carried on this institution of contract law through the theory of relational contracts developed by Ian R. Macneil or the contrat-cooperation theorised by Suzanne Lequette. This theory invites to take into account the intrinsic value of the contractual link and the incompleteness of the contract. Imprévision thus forms integral part of the relational contracts from their nature. The primary purpose of the relational contrat is to continue, forcing the contractors to standards of cooperation and flexibility. According to good faith, the relationnality would be the foundation of changed of circumstances. A comparative study of the regime of changed of circumstances makes certain clarifications. There appear two approches of the changed of circumstances, one restricted based on economic modifications, and the second wide one, based on the purpose or foundation of the contract. Finally, the effects of the changed of circumstances should give priority to maintain the relation and the norm of cooperation by imposing renegotiation then by allowing judicial adaptation of the terms of the contract. Termination, contrary to the nature of relational contracts, should intervene only exceptionally.

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「天有不測風雲，人有旦夕禍福」，生活中往往有不可預測的變故發生，而使社經環境波動、人之資力與其他履約相關能力受到影響。另一方面，貿易全球化、工商業分工專業化，以及電子商務的崛起等，均使交易型態日趨複雜；在契約當事人的有限理性下，欲以契約窮盡規範工商業上所有可能事態，實屬不易。履約環境若如契約締結時當事人之預想，且兩造亦依契約規定確實履行，自是最佳；惟契約之締結與履約行為若非同時發生，在時間上存在間隔而使履約環境暴露於變動風險中，而當事人締約時未加以規範，或有規範但程度超乎預期之變故發生，將可能導致一方當事人難依原契約履行，或依原契約履行已無意義。 　　在傳統私法自治、契約嚴守的概念下，即便遭遇前揭無法預測或預測不完全之變故，仍應依契約履行，而無法律介入之餘地。但毫無彈性的強制履行契約，不論就公平角度，抑或經濟效率而言，對當事人與社會或非妥適；因此，多數國家均將處理情事變更之制度納入法律體系中，以期獲致一較理想之結果。 　　本文首就我國情事變更原則之演進暨學說見解作一整理，並以現行情事變更原則(民法第二百二十七條之二)與我國民法中近似之概念(如不可抗力、動機錯誤)，以及同樣處理「法律行為成立後之情事變更」相關民法法條（如不動產租金因價值升降之增減請求權）互為比較。第三章比較法部分，則以德國「法律行為基礎理論」、美國「履行不能、履行艱難、目的受挫」等規定為標的，敘述其演進及要件，並就其要件及效果與我國情事變更原則比較。第四章以我國近五年最高法院判決為本，依民法二百二十七條之二諸要件，分點探討最高法院與我國學說間見解之異同，並特就「非當時所得預料」及「顯失公平」兩點，觀察最高法院就此之評價方式。第五章則以對我國學說與實務之建議，作為本文之結論。 / Accidents happen from time to time and may seriously change the social and economic environment and affect people’s condition, including their ability to fulfill the contractual duties. At the same time, globalization, professionalization of services and eCommerce all make trades much more complicated than ever. As a result, under bounded rationality as well as finite contract clauses, using contracts to govern almost unlimited possibilities seems like asking for the impossible. The best case for the contractual parties is no unpredictable event happens after the constitution of the contracts; however, if a time gap exists between the entering into and the performing in full of a contract, there can be accidents which lead to the impossibility / impracticability for a party to fulfill the contractual duty, or the performance of a contract becomes meaningless (frustration of purpose). Under the principles of autonomy of private law and strict performance of a contract, there shall be no relief for a party which encounters the foregoing situations of impossibility, impracticability and the frustration of purpose. However, from a fair point of view, asking one party to bear all the disadvantage resulting from an unforeseen event and perform all its duties disregarding the cost may not be the best answer; therefore, in order to introduce more flexibility for the jurisdiction and the contractual parties, countries all over the world gradually adopt the principle of change of circumstances (and similar regulations) which may help to achieve an acceptable result. In this thesis, the principle of change of circumstances in our civil law will firstly be discussed, including its development as well as the elements and effects set forth in Article 227-2; then, two comparisons “(1) between Article 227-2 and similar concepts (force majeure, mistake...)” and “(2) between Article 227-2 and other Articles in our civil law dealing with the events occurring after the establishment of legal relations” will be conducted. In chapter three, the analysis of the regulation in Germany and the United States regarding change of circumstances is carried out. A historical German law review precedes the discussion of current BGB §313 “Störung der Geschäftsgrundlage”, and a comparison between Taiwanese and German regulation is given. After that, the United States’ regulations regarding the doctrine of impossibility, impracticability, and frustration of purpose are discussed in the same manner. At last, a summary comparison among the three countries is served as the conclusion of this chapter. In Chapter four, our Supreme Court’s 162 verdicts from year 2009 to 2013 are analyzed by the elements of Article 227-2, which are: (1)after the constitution of the contract; (2)changing of circumstances happens; (3) such change of circumstances is not predictable; (4)the performance of the original obligation will become obviously unfair; (5) by the party’s application, the court may increase or reduce his payment, or alter the original obligation.At the end, few suggestions for future legislation and Supreme Court’s application of Article 227-2 are given as the conclusion of this thesis.