Edited by Burkhard Mojsisch, Olaf Pluta and Rudolf Rehn
[Bochumer Philosophisches Jahrbuch für Antike und Mittelalter 10] 2005
► pp. 21–36
Wenn die Möglichkeit in Notwendigkeit umschlägt
Ein Beitrag zur Vorgeschichte modaler ontologischer Beweise
Aristotle produced several arguments to vindicate the futura contingentia and to refute the conception of modalities which do not allow incidental facts. This conception was coined mainly by Diodorus Cronus and implied the view that whatever may happen, is to happen necessarily. Although Aristotle condemned this view and refuted the theology which it implies, Diodorean modalities were employed by the scholastics (at least since Abaelard, as Leibniz pointed out) to support their theology. Abaelard’s Diodorean formula reads: God wishes (and ultimately cannot but do) no more and no less than what He is able to do – i. e. God’s ability to do something implies necessity. In the Summa theologiae, Thomas Aquinas employed Diodorean modalities along with this result of Abaelard’s. Leibniz himself confessed his debt to Diodorean modalities as well as to the work of Abaelard in formulating his own ontological proof. Kurt Gödel was under the influence of Leibniz when he wrote his »Ontological Proof«, which employs Diodorean modalities. — For the Greek-speaking scholars of the Middle Ages, however, Aristotelian influences were stronger than Diodorean as regards theory building on modalities. Philosophers from the East from the 2nd to the 11th century A.D., such as Alexander of Aphrodisias, John Philoponus and Michael Psellos, condemned Diodorean modalities as fallacious. In the same period, Greek Church Fathers such as Cyril of Alexandria, Maximus Confessor and John of Damascus gave an orthodox account of God and the modalities, according to which (contrary to what Abaelard says) God is able to do whatever He wishes. The absence of Leibniz-like modal ontological proofs in the Greek tradition seems more plausible under these circumstances.