The concept of the origin of contract obligations is one of the fundamental issues in contract law and the basis of obligation of legal rules is different from the legal sanctions of the law. There are four main views on the origin of contract obligations: the will of the parties, the will of the state, the social will, and natural justice. The effect of each aspect in the superiority of one principle over another is different. The present research, conducted using a descriptive-analytical method, in response to the question of under what conditions natural justice constitutes the origin of contract obligation and what its practical consequences are on contract law, concludes that, based on the will of the parties, the principle of binding force prevails and the sanctity of the contract is always the dominant aspect. Based on the will of the state, any inconsistency of the wills with the law will invalidate the contract. Based on social will, the validity of a contract is based on custom. In the natural justice approach, principles such as good faith are predominant, prevail over other principles such as the principle of binding force, and also play a significant role in the interpretation of contract. In the Iranian legal system, due to pluralism, it appears that natural justice and natural morality constitute the main basis of obligation; however, other bases also play a role alongside them