Published online by Cambridge University Press: 01 January 2020
In What is a Law of Nature? (1983) David Armstrong promotes a theory of laws according to which laws of nature are contingent relations of necessitation between universals. The metaphysics Armstrong develops uses deterministic causal laws as paradigmatic cases of laws, but he thinks his metaphysics explicates other sorts of laws too, including probabilistic laws, like that of the half-life of radium being 1602 years. Bas van Fraassen (1987) gives seven arguments for why Armstrong's theory of laws is incapable of explicating probabilistic laws. The main thrust of the arguments is that Armstrong's metaphysical apparatus serves to drive up the initial probability values stated by probabilistic laws. Armstrong replies to van Fraassen in his (1988) and (1997) by appealing to limiting relative frequencies. Remarkably little has since been written about Armstrong's theory of probabilistic laws and I wish to revive interest in the debate here by assessing Armstrong's response. I will argue that his response fails because the principle of instantiation puts the limiting relative frequencies that he requires out of reach.