TY - JOUR ID - 35748 TI - Invalidity of “Subject-Obversion” Rule JO - Philosophy and Kalam JA - JITP LA - en SN - 2008-9422 AU - Azimi, Mahdi AD - Assistant Professor in Islamic Philosophy at University of Tehran Y1 - 2013 PY - 2013 VL - 46 IS - 2 SP - 83 EP - 100 KW - subject-obversion KW - most extensive universal KW - Islamic Logic DO - 10.22059/jitp.2013.35748 N2 - In contemporary texts of Islamic logic, the “subject-obversion” has been introduced as a rule on basis of which one can replace the subject term of a categorical proposition with its complement and change both quality and quantity of the proposition. Thus from an A-proposition such as “all A is B”, one can infer “Some not-A is not B”. Well, let’s take that A is included by B but not vice versa, and B is most extensive universal such as “existent” or “thing”. In this case “all A is B” produces the contradictory of our favorite conclusion, i.e. “all not-A is B”. Therefore, the so-called subject-obversion rule, at least in A-proposition, is not logically valid. UR - https://jitp.ut.ac.ir/article_35748.html L1 - https://jitp.ut.ac.ir/article_35748_e353211cc588ac9cc43d0108c9dc4956.pdf ER -