Let's say I have a bag of fifty ordinary chrome steel balls. They are of the same size up to a tolerance of 0.01 mm, but they do exhibit minor size variations below that tolerance. So one of these steel balls is smallest. On Lewis-type accounts of counterfactuals, we have to say that:
- If one of the balls were made of brass, it would be the smallest of them.
But while we intuitively think that (1) might turn out to be true, it shouldn't turn out to be true simply because of such size considerations.
This is a non-temporal version of the coat thief problem (see, e.g., p. 42 here).