In the 1950s and 1960s, the neoclassical theory of the firm was criticized for its unrealistic assumption and the assumption of zero transaction costs, was questioned. According to the North perceptions of Coase theorem abut transaction costs, although in neoclassical imaginary world that is based on "transaction costs are equal to zero" assumption, market mechanisms can create efficiency without institutional arrangements that define the rules of the game but in the real world that transaction costs is positive, institutions (legal rules) have effect on the allocation of resources. Thus, the Coase theorem clarifies the relationship between transaction costs and legal norms. Transaction costs are costs that parties paid for information gathering, or non-performance of contract by the other party, or to be incurred for monitoring and enforcement of contracts.Because contracts are incomplete that means the mutual rights and obligations of the parties have not been agreement in many cases and therefore it is not mentioned explicitly in the contract so not to mention the rights and obligations means there is a gap in the contract thus one of the main functions of a legal system abut contract law would do to fill this gap by defining the supposed rules. By definition, the assumed rules are including rules that determinate mutual rights and obligations of parties for possible states that usually are not defines in contracts. Therefore, with considering to conditions for contract can be improved somewhat flaw in the contract. Terms and provisions of the contract in Islam, and investigate of the moral and religious principles governing on Islamic contracts, show that there are teachings that can greatly due to transaction costs reduction, efficiency increase and satisfaction of parties in contracts.

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