The doctrine that holds that it does make sense to ask – without reference to common attributes and behavior – whether this is the same individual in another possible world … that a common “thisness” may underlie extreme dissimilarity or distinct thisnesses may underlie great resemblance, I call Haecceitism …

The opposite view, Anti-Haecceitism, holds that for entities of distinct possible worlds there is no notion of transworld being. They may, of course, be linked by a common concept and distinguished by another concept – as Eisenhower and Nixon are linked across two moments of time by the concept the president of the United States and distinguished, at the same pair of moments, by the concept the most respected member of his party – but there are, in general, many concepts linking any such pair and many distinguishing them. Each, in his own setting, may be clothed in attributes which cause them to resemble one another closely. But there is no metaphysical reality of sameness or difference which underlies the clothes. Our interests may cause us to identify individuals of distinct worlds, but we are then creating something … of a kind different from anything given by the metaphysics. Although the Anti-Haecceitist may seem to assert that no possible individual exists in more than one possible world, that view is properly reserved for the Haecceitist who holds to an unusually rigid brand of metaphysical determinism.