Medieval Philosophy

by Peter S. Adamson

would remain inert, having nothing to act upon. In fact, even two principles wouldn’t be enough, since they would cancel each other out. In late antiquity, though, all philosophers accepted that the universe derives from one cause, with the pagan Neoplatonists identifying this cause as the One or Good and the Jews and Christians, of course, seeing the God of their Scriptures as the almighty Creator of all things. Still, like an offer of marriage from a Montague to a Capulet, the proposal continued to cause trouble. Philosophers worried less that a single cause would remain entirely inactive, as Aristotle claimed, and more that such a cause could only have one effect. The Neoplatonic First Principle and the Judeo-Christian God were claimed to be perfectly simple, and how can a perfectly simple thing generate a multiplicity? Only indirectly, claimed the Neoplatonists. Their One would produce only one effect, which would form a link in a causal chain stretching down all the way to our physical realm. We might expect thinkers of the Abrahamic faiths to abandon this scheme in favor of direct creation of each thing by God. Many thinkers of Judaism, Christianity, and Islam did precisely that. But those with a greater commitment to the Hellenic heritage adhered to the rule “from one thing only one thing can come,” in Latin ab uno non nisi unum. It’s a motto that became notorious in both the Arabic and Latin spheres. In the Islamic world the theologian al-Ghazālī attacked Avicenna ...