In the above passage, inadvertently perhaps, St Thomas admirably hits off the real meaning of what he and Aristotle called 'contingent' events, symbebêkota. An event is 'contingent' in reference to a particular system, but (apart from the doings of free will) every event is 'necessary' in the 'general system,' on the hypothesis of that system being. The killing of a sheep by lightning (see note [3.94a])is a contingency unprovided for in ovine economy, but pre-arranged in the general system of the universe, in which general system it is an hypothetical necessity: it must be, if the system is to stand as it is.

Of God and His Creatures: 3.95