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Published online by Cambridge University Press: 03 July 2018
We care not just how things are but how they could have been otherwise – about possibility and necessity as well as actuality. Many philosophers regard such talk as beyond the reach of respectable science, since observation tells us how things are but (allegedly) not how they could have been otherwise. I argue that, on the contrary, such criticisms are ill-founded: possibility and necessity are studied in natural science, for example through phase spaces, abstract mathematical representations of the possible states of a physical system. The possibility is objective, not merely epistemic, though it may be more restricted than pure metaphysical possibility. The elements of a phase space are very similar to Kripke's possible worlds, despite being time slices rather than total histories. The absence of explicit modal operators in the mathematical models used by scientists does not show science to be non-modal; rather, it manifests reliance on a mathematical framework for theorizing about objective possibility similar to the mathematical framework of possible worlds model theory.
1 This paper descends from a lecture given at the Royal Institute of Philosophy, where it received useful feedback. For a more detailed and rigorous development of the ideas in it, see Williamson, Timothy, ‘Modal Science’, Canadian Journal of Philosophy 46 (2016): 453–492CrossRefGoogle Scholar. More general issues about the status of modal logic are treated in Williamson, Timothy, Modal Logic as Metaphysics (Oxford: Oxford University Press, 2013)CrossRefGoogle Scholar.
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