Modality in medieval philosophy

The synchronic conception of possibility and necessity as describing simultaneous alternatives is closely associated with Leibniz and the notion of possible worlds. The notion seems never to have been noticed in the ancient world, but is found in Arabic discussions, notably in al-Ghazali in the late eleventh century, and in the Latin west from the twelfth century onwards, elaborated in particular by Scotus. Scotus considers a further argument for the necessity of the present which appeals to a particular rule in obligational disputations—a genre peculiar to the late middle ages, developed throughout the thirteenth century and prevalent in numerous philosophical works in the fourteenth. Buridan was one of the few logicians in the Middle Ages who developed his own system of modal logic, distinct from and independent of Aristotle’s system. Most others felt constrained to follow Aristotle’s lead, even if they gave it their own semantic basis, and struggled in the attempt.