Document Type : Extension

Authors

• Nasrin Seraji poor ¹
• Elaheh sadat Agha seyyed yusef ²

¹ Imam Sadeq University

² Tehran Univercity, Tehran

Abstract

Avicenna's innovation on Conditional Categorical Syllogism is known as a turning point in Islamic logic. Conjunctive conditional syllogism is accepted as valid; but there are some problems and different opinions about Disjunctive syllogism. In his works, He mentions various conditions to determine the truth-value of Alternative syllogism and considers the Exclusive disjunctive syllogism as invalid. Following Avicenna's thoughts, Nasir al-din Tusi declares the Exclusive disjunctive syllogism invalid and holds that syllogism consists of two disjunctive propositions that are not valid either. Agreeing with some of the general conditions of the syllogism, other contemporary logicians namely Afzal al-din Khunaji and Siraj al-din Ormavai declares the two types as valid. It seems that the only way to solve the disagreement between the logicians on this issue is to change premises into the conjunctive syllogism and then follow the rules of conjunctive and finally reach the conclusion through changing Conjunctive into Disjunctive Syllogism.

Keywords

• "Conditional Categorical Syllogism"
• "Alternative denial"
• "Exclusive disjunctive proposition"
• "Disjunctive proposition"
• "Avicenna"