  As in possible world semantics, the modal operators ‘□’ and ‘◇’ “turn into” quantifiers over worlds in concretist truth conditions (1986, 5). Also as in possible world semantics, a quantifier (in effect) ranging over individuals that occurs  in the scope of a quantifier (in effect) ranging over worlds — ‘∀x’ and ‘∀w’, respectively, in (18) — is, for each value w of the bound world variable, restricted to the objects existing in w. However, unlike possible world semantics, predicates are not to be thought of as having different extensions at different worlds. Rather, for Lewis, each (n-place) predicate has a single extension that can contain (n-tuples of) objects across many different worlds — intuitively, all of the objects that have the property (or n-tuples of objects that stand in the relation) expressed by the predicate across all possible worlds. Thus, in particular, the predicate ‘G’ picks out, not just this-worldly dogs but other-worldly canines as well. Likewise, the pet predicate ‘T’ picks out both actual and other-worldly pets. Such a move is not feasible in basic possible world semantics, which is designed for a metaphysics in which one and the same individual can exemplify a given property in some worlds in which they exist but not others. Hence, a typical predicate will be true of an individual with respect to some worlds and false of it with respect to others. But, for Lewis, as we've seen, distinct possible worlds do not overlap and, hence, objects are worldbound, thereby eliminating the need to relativize predicate extensions to worlds. 