Qur'an, the Book of God, is in Arabic; God has made His book one of the eternal miracles of the His last prophet. God has called all people to ponder the Qur'an and the deniers of this miracle to bring a book like the Qur'an and Its verses. One of the prerequisites for an exploratory reference to the Qur'an is knowing the Arabic language, and the higher the degree of this reference, the more necessary it becomes to know the Arabic language. Arabic is one of the most powerful languages in the world of language. The most famous sciences in this language are morphology, syntax, semantics and expression which constitute the science of rhetoric. The translation and interpretation of the Qur'an are not possible without knowing these sciences, and part of the power of translation and success in interpretation depends on the degree of mastery over them. Some of the rules contained in these sciences are less included in their famous texts; at the same time, the significant effects of these rules have been included in some of the interpretive texts. This article discusses one of these rules; the rule of tazmin.