The Ex turpi causa non oritur action, ex dolo malo non oritur action maxim and Illegality defense

litigants sometimes refer to own wrongdoing and expect the courts to rule in their favor. If such lawsuits or defenses are accepted, justice will not be done and a solution must be found to solve this legal problem. In this case roman maxim " Ex turpi causa non oritur action, ex dolo malo non oritur action " are cited in legal systems . The most important thing about that is the concept and scope of its application. Therefore, the concept and scope of this maxim was examined in some legal systems, especially common law system, and some instances of it were researched. It became clear that in most legal systems, this principle is considered a certain legal principle. This maxim cited in foreign law in three sections: contracts, civil liability, and trust. The meaning and rules of applying this maxim in foreign law are not very clear; However, legal principles and policies and methods have been proposed to apply it, and there are instances such as illegal transactions, bribe restoration, slayer rule, and the responsibility of the offending managers to company, Which sometimes was criticized and Has been set aside. This maxim have a moral basis and considered as a requirement of justice. However, in practice, in order to avoid its mechanical application, its application is at the discretion of the judge, and this is done with the balance of the importance of the wrong and the amount of damage, and with Considering such rules as prohibition of unjustified enrichment. Islamic jurisprudence and Iranian law like any other legal systems, has it inside. This maxim can also be considered in litigations, and as a procedural rule prevents the parties from invoking their violations and prohibits the hearing of lawsuits or defenses that documented with violations of the plaintiff or defendant