Modal Realism and Inductive Scepticism

Abstract

I wish to argue for an objection to David Lewis's modal realism that goes roughly as follows: Acceptance of Lewis's theory makes radical scepticism with respect to induction unavoidable, and whatever attractions the theory may have, this is too high a price to pay for accepting it. Versions of this objection have been formulated by Peter Forrest, George Schlesinger, Robert Adams, and J. J. C. Smart, among others. I will call it 'the Objection from Scepticism'. It is possible, of course, to argue that relying on induction is unreasonable, period-not merely for the modal realist, but for anyone. Let us call such an argument a 'Hume Argument' since several instances are to be found in Hume's Treatise and Enquiry. In response to the Objection from Scepticism, Lewis suggests, in effect, that any argument for the conclusion that the modal realist cannot reasonably trust induction must really be a Hume Argument in disguise. If the Objection from Scepticism is really a Hume Argument, then it is illegitimate; Hume Arguments tar everyone with the same brush, and so cannot provide the basis for a legitimate objection to anyone's theory in particular. I will try to formulate the Objection from Scepticism so as to make it quite clear that it is specific to modal realism. But it is worth considering whether the objection might, after all, have a connection with some Hume Arguments. Few, if any, philosophers are willing to embrace scepticism towards induction, but it is often difficult to see what is wrong with a particular Hume Argument. Perhaps what is wrong with some Hume Arguments is that they implicitly incorporate one or more assumptions to which not everyone is committed regardless of his theory of modality. If this is so, then the Objection from Scepticism may be interesting