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Cause / Place (all other ditto): their effects are contingent - (s) a posteriori (empirically) found - and the cause may be conceptually nothing more than the cause of an effect - Hume: he was aware that the sentences that attribute necessity between tokens of situations, in turn, are contingent.
AR II = Disp
D. M. Armstrong
Dispositions, Tim Crane, London New York 1996
What is a Law of Nature? Cambridge 1983