‎“Exchange Liability” in Islamic and Iranian Law ‎and Its Comparison with “The Theory of Cause” ‎in French Law

One of the most important issues in synallagmatic contracts is the liability in contractual consideration. All legal systems have faced this problem and have proposed rules to solve it. In Islamic law, this is referred to as “Exchange Liability". But in French Law, it is known as the "theory of cause", which is the most important concept in contract law. The purpose of this study is a comparative study of the concept, basis, and nature of "Exchange Liability" and "theory of cause". This will be done in a descriptive, comparative, and analytical method. According to the findings of this study, Exchange Liability is a kind of “voluntary liability” whether it is the result of a valid or invalid contract. And the theory of cause has a similar role in civil law. Despite the similarities between these two theories, there are also differences, especially in terms of territory.One of the uses of liability in contractual relations is the “exchange liability”. The delivery of the exchange in exchange contracts is not achieved once the contract is concluded, but it is a mutual obligation that each of the parties undertakes to fulfill by concluding the contract. Even though there are many branches and examples of the exchange liability in Iranian law and the exchange liability has been recognized in a broad sense; however, in Iran's legal sources, this type of liability is referred to as "compensatory liability"; in connection with the discussion of Article 387 C.C. In jurisprudential sources, it is described as "exchange liability". Although there are various theories in the legal systems such as "Cause", "Consideration" and "exchange liability" to create and adjust the balance between the exchange parties in a reciprocal contract, they all have a common goal and to some extent a meaning.Liability for the contractual exchange is mentioned in all reciprocal contracts and exists in the stage of the execution of the contract even in the assumption of loss of exchange and cancellation or liquidation of the contract. with the implementation of its effects, it means delivering exchange or its substitute, will be expired. Lawyers in the Roman-Germanic system have proposed the "theory of cause" to determine a standard as a basic element in the validity of contracts and as proof of the seriousness and commitment of the parties to their obligations.  The main question of this study is: what is the relationship between “exchange liability" in Islamic and Iranian law and the "theory of cause" in the Germanic Roman system?This research shows that to create and maintain balance and justice in reciprocal contracts, the Islamic law has provided “exchange liability". The concept of “exchange liability" is the responsibility for the contractual exchange, and the concept of the “theory of cause” is to express the necessity of the existence of a cause for the contract from its creation to its execution. The emphasis of the “theory of cause” is more on the existence of the legal act, while the emphasis of the “exchange liability" is more on the nature of the reciprocal contract and the guarantee of the performance of the tasks contained in it. From the point of view of the content of the “exchange liability", it is a mandatory rule, and it is not considered a financial right. The “cause” is also independent and separate from the character of the contracting party, and it is the same for every type of contract and is related to its legal structure. "Cause" is a real and logical truth, which is impossible to ignore. Both concepts have a similar basis, including being rational and establishing a balance between the parties, and preventing the loss of the parties. However, the domain of the “cause theory” is beyond the domain of “exchange liability", because it includes non-reciprocal contracts and even events. But from another point of view, the “exchange liability" has a wider scope. Because in principle, the existence and manner of creation, the necessity, and manner of execution of the contract, in the assumption of loss of exchange, annulment or liquidation of the reciprocal contract, in the assumption of non-execution of the contract and the emergence of contractual liability, and the manner of implementation of the effects of this liability and the number of compensable damages, have an effective presence.