The Great Western Railway

In On The Plurality of Worlds Lewis presents the case of the Great Western Railway as a candidate counter-example, along with the usual suspects, to the thesis that two things cannot be in the same place at the same time. Typically, pluralists or many-thingers, i.e., those who reject the thesis, point to modal or historical or aesthetic differences to justify their judgement of non-identity. Lewis’s aim to is to show the inadequacy of this justification, at least as regards modal differences, by considering a case in which it clearly fails, in which the judgement of non-identity so based is incredible, and hence to make it evident that in all such cases the appeal to modal differences is insufficient. What makes the case of the Great Western Railway special is that it is a purely spatial example, as Lewis emphasises. In what follows I set out the example and try to make it clear that, as Lewis says, for this reason a judgement of non-identity based on an appeal to modal differences is incredible. Then I give another example, easier to understand, I think, which makes the same point, inspired by Russell’s famous joke about the irate yacht owner.