the author intend to by studying the historical causes of the appearance of the novation in the west and explanation of its legal nature from past to present of french law, proves on the one hand that the novation does not extracted from the french civil code and in the shiite jurisprudence with quite similar terms even before the enactment of iranian civil code, was considered by the shiite supreme jurist and on the other hand prove that the novation is not a legal act but this is a legal effect as a result of legal actions, legal events or legislative decree and contrary to the famous idea, is an effect and is not the cause. the author believes that this idea terminate to the theoretical disputes and present the quiddity of the novation in the best possible expression.