I mentioned before that Robert Caubraith's Quadrupertitum (1510) explicitly sanctions or-introduction. It turns out that so do Ockham's Summa Logicae II.33 (c. 1323) and Buridan's Tractatus de Consequentiis III.1.5 (c. 1335), not to mention Albert of Saxony's subsequent Perutilis Logica (1350s?). The licence is also implicit in William of Sherwood's Introductiones in Logicam I (c. 1245?) and Walter Burley's Tractatus Brevior 280,285 (c. 1320?) and Tractatus Longior II.3.i 548,551 (c. 1326?).
Does this mean that Auriol stands alone among his contemporaries?
Well, Giles of Rome (d. 1316) is thought to have followed Boethius (De Hypotheticis Syllogismis) in treating disjunction as exclusive, in which case he would have denied or-introduction as a rule of inference. But as I said before, the incompatibility of the two disjuncts in our particular case (‹Antichrist will be›, ‹Antichrist will not be›) renders such considerations inoperative. So this is unlikely to be relevant to Auriol's denial.
3 months ago