A 'contingent event' is an event that depends on what Mill calls a 'plurality of causes': that is to say, a certain number of causes being jointly present; and again preventing causes, almost innumerable, being all absent. The absence of any of the requisite joint causes, or the presence of any of the preventing causes, is enough to wreck the sequence; and as we cannot well know what cause will be present, and what absent, the event to us looking forward is an uncertainty, something that may or may not be; and looking back upon it, after it has happened, we regard it as something which has been, but might not have been. But, to an omniscient mind, all events, so far as they involve mere physical causation, are hypothetically necessary: they must be, causes and conditions standing as they do. This hypothetical necessity of physical causation is otherwise called 'the uniformity of nature.' With this chapter, Book II, Chap. XXX should be compared: see also B. II, Chap. LV, footnote. Human acts, or acts of free will, which are not even hypothetically necessary, are not included in the category of contingent events here spoken of.
Of God and His Creatures: 1.67