Counterpart relations are certain similarity relations between individuals.1 A counterpart relation is the resultant of similarities (and dissimilarities) in various respects, where similarity in a given respect is a matter of degree and similarities in different respects (to the same degree) may be differently weighted. In GR, counterpart relations are invoked in order to explain how a possible world (or a possible individual) represents, de re, of an individual that it has a given feature – primarily, to explain what it is for it to be the case that at a world, w, a is F – thus: Lewis (1968, 1971, 1973: 39-43, 1983b and 1986a: Chapter 4).2 In this respect Lewis invokes counterpart relations as an alternative to transworld identity of world constituents (see Chapter 16). As a quite general observation about representation de re, it is clear that an individual may be represented (even in its absence) as having a certain feature by means of simulacra. Thus, for example, Clinton may be represented as sitting by a human lookalike who sits, by a painting of him sitting, by a wax dummy modelled in a sitting pose, etc. As an instance of this sort of representation, Lewis proposes that a world w may represent de re of an individual x (even when x is not part of w) that x has a certain feature F by w having as a part an individual y that is a suitable simulacrum – a counterpart – of x and which is F. Thus, for example, the possibility of Clinton sitting is represented by a world containing a counterpart of Clinton who sits.3