On the conversion of modal propositions, Afzal Al-Din Al-Khunaji has many innovations accepted by all logicians coming after. Pursuing the issue in Aristotle, Avicenna, Al-Razi, and Al-Khunaji, we show that the gradual changes from Aristotle to Al-Khunaji make a spectrum with seemingly no similarity between its two ends. In fact all Aristotle's views on the modal conversion have been rejected by Al-Kunaji. Al-Kunaji's successors, although accepted his views on the conversions of the actuality propositions, denied or disregarded his views on the verity propositions. Consequently the conversion of verity propositions vanished from their logic books. In this paper, we confine ourselves only to the conversions of the actuality propositions. With the aid of modern logical formalizations, we shall show that in all disagreements between Al-Razi and Al-Khunaji, the latter’s views were the right ones, hence the total acceptance of his ideas by his successors
)
