Reasonableness is the main principle in contract law,which, according to the characteristics of all kinds of rationality and custom,with the aim of contractual justice and with the guarantee of certain performances,assesses the real and objective conditions of the contract.This principle has wide legal implications in the legal systems of the world and must be observed in the formulation of law,conclusion, execution and interpretation of contracts.In many important international documents including the principles of European contract law and the domestic law of some countries,including the United States,Germany,Italy,it is explicitly recognized as one of the important principles of contract law that protects individuals in contractual relations.The economic efficiency of this principle is such that as a legal standard and tool it helps contractors who are trying to achieve contractual justice in the exercise of their rights,given the available economic and information resources.The effects of this principle are such that the parties,despite the principle of freedom of contract, can not ignore it.In Iranian contract law,Reasonableness as a legal principle has not been considered so far;While its legal grounds and sources,including Article 167,existed;and the use of this principle,especially in the interpretation of the legal rules of the contractual field,can create a fair basis in the qualitative method of legal citation and argument.Some findings indicate the possibility of modification and cancellation of the contract or its terms by appealing to the principle of reasonableness.Ultimately,the goal is to incorporate the principle of reasonableness into the general rules of Iranian contracts to aid the contractual justice process
