A Critical Examination of the Six Views on Inference Conditions of Exceptive Syllogism in Avicennian Logic (With Emphasis on Connected Conditional)

The present essay is dedicated to review and criticize the different Avicennian logicians’ ideas on the inference conditions of exceptive syllogism. After reviewing numerous texts of Avicennian logic, those views are classified into six categories. In the first category, conditional in exceptive syllogism is used as indefinite, which is not consistent with Avicennian logical foundations on conditionals. By ignoring this idea we realize that all Avicennian logicians agree upon the necessity of conditionals as a requirement for inference in exceptive syllogism and the possibility of inference from universal affirmative hypothetical. However, there are disagreements about the possibility of inference in exceptive syllogism from universal negative conditional, particular conditional and singular conditional. Finally, with a logical analysis and based on evidences from natural language, we have made judgments about these disagreements. The following outcomes are the results of our analysis: In these syllogisms, the conditional premise should be universal and necessary; Inference in exceptive syllogism from negative conditional depends upon the disputes concerning the relation between the necessity of negation and the negation of necessity, and determining the interpretation of negative conditional; Exceptive syllogism whose conditional premise is singular yields a valid inference only if the temporal or modality of truth in conditional and exceptive syllogism is the same.