Re-reading the definition of conversion with emphasis on the drawbacks of Mohaqeq Tusi on Ibn Sina

Farabi is the first Muslim logician to define conversion in his works. Ibn Sina, by borrowing from him and adding the adverb "survival of falsehood", has defined the conversion as follows: " Displacement of the subject and predicate along with the survival of the quality, truth and falsehood.". The logicians after Ibn Sina, led by Tusi, have found several inaccuracy in this definition and have tried to provide an accurate and consistent definition with the logical system. In this research, while measuring and evaluating these problems and answers, the historical course of definition of conversion by Muslim logicians has been studied. For this purpose, the evolution of the definition of conversion has been studied and by mentioning the problems of the definitions of logicians such as "Farabi", "Akhavan Al-Safa", "Fakhr Razi", "Ibn Sahlan Savi", etc., we have been led to the conclusion that "Khunji" and his contemporaries definition ("Tusi", "Ermoi", etc.) is a suitable and correct definition.