From the perspective of experts, custom as moral rules binding takes place in source of law. However, clarify its position in constitutional law needs to know history of custom presence in basic documents which govern on human societies. Known dividing Constitutions into two main categories, codified and customary, only will be clarified part of the extensive. Because above division, as many experts believe, is a relatively division and codified Constitutions, also have custom backgrounds in their standards and structures. On the other hand, similar concepts like law general principles have to distinguish from customary norms and basic principles governing constitutions, because integration and separation of these concepts from each other, creates many scientific works in legal systems. In addition, mechanisms of formation each one of the two concepts is deferent and custom standards rely on material and spiritual elements. In between, development constitutional law customs move distinguish way. Because this development extend in some legal systems is more than other systems and different role of custom in formation of basic and fundamental rules in several legal systems, extends to opinions of public law experts about position of custom in constitutional law systems. Hence, to obtain common understanding of custom role in constitutional law, so sure role of custom in meaning of confirm of its interpreter and suffice to common opinions of the experts.
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