Promise de port fort is an useful legal basic for justification many civil and commercial transactions. Such as bank guaranties, insurance and guaranty of things it divides two legal relations, relation between parties if third party not ratify and relation with third party if she or he ratify that promise. Unlike its appearance, it, is not violation the principle of relativity of contracts. because, there is not an obligation to third party. This research has been allocated to study its legal aspects and its affects. By this basis we are free from limitations of contractual guaranty upon Iranian legal system such as cause and transfer of dept.
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