The problem of commutative justice has been widely analysed by the contemporary doctrine of civil law. Simultaneously there is a profound debate about the meaning of commutative justice and equivalence in exchange within the sphere of moral philosophy. All these issues seem to concern the problem of interdependence between parties. Such interdependence is called synallagma or the principle of synallagma. In this paper I would like to present the concept of synallagma in civil law and in philosophy of law. Since the dispute in both disciplines seems to be unresolved and inconclusive, I would like to present the two economic theories concerning synallagma as the strategic interaction between agents. The most appropriate tool to be implemented seems to be the game theory. In conclusion I would like to address the question whether substantial and objective equivalence in contracts is possible or under which conditions it is meaningful.