  On the other hand, the monadic predicate “is a thing”, the dyadic predicate “is identical with”, and the quantifier “everything” do not distinguish between Lucky Feet and the Statue of Liberty. In fact, they do not distinguish between any two particular objects. As far as they are concerned, one object is as good as another and might just as well be switched with it. Expressions with this kind of indifference to the particular identities of objects might reasonably be said to be topic-neutral. As we will see in the next section, this notion of topic neutrality can be cashed out in a mathematically precise way as invariance under arbitrary permutations of a domain. It is in this sense that the basic concepts of arithmetic and set theory are not topic-neutral, since they distinguish some objects (the empty set, the number 0) from others.