Counterparts and Comparatives
terpart of a's in some world is taller than a. At least, that's how things work out in David Lewis's counterpart theory (as presented in [7]). This is such a neat and direct way of expressing the content of modal comparisons that we should do well to give it up only when faced with weighty counter-evidence. Misgivings about the semantics of comparatives and the ultimate metaphysical basis of 'crossworld relations' such as are involved in comparisons between a and its counterparts do not constitute such evidence. At best they suggest that the neat and direct analysis does not yield the whole story, not that no attempt should be made to express such locutions in first-order counterpart theories nor that nothing may be learned from so doing. On the face of it, we do make comparisons between things as they are and as they might be (and even more obviously between things as they are and as they were or will be). Without prejudice to metaphysics and the semantics of comparatives I shall take these comparisons at face value. If they are to accommodate them at all, counterpart theories must do more than simply allow us to express modal comparisons. They must allow of extension in order to enable us to account for the fact that certain arguments involving modal comparisons strike us as valid. I have in mind arguments such as: