Contracts can be divided into voidable contracts and necessary contracts in terms of stability and instability. Principle of obligation will be applied to cases where one side of bargain cancels the contract without the satisfaction of the other side- after it has been made. According to the principle of obligation, however, the contract is valid and cancellation will not take effect. The rule of obligation is considered to be an essential, universal one in the area of bargains. Obligation of contract can be interpreted on the basis of overriding of necessary contracts, of the jurisprudential rules, the practical principle of Istishab (i.e…), of the decision of the wise, and of the principle of established norms. Some lawyers attach the principle of obligation to expediency and explain the former based on the latter. The Shiite have sought the reasons behind the above-mentioned principle in the Qur'anic verses, in Islamic traditions, in the conduct of the wise, and finally in the practical principle of Istishab. The Sunnite jurists have also dealt briefly with the principle of obligation.
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