To complete this discussion of ontological naturalism, let us briefly consider the realm of modality, understood as the subject matter of claims that answer to something more than actuality. Modality raises many of the same issues as mathematics, but the topic is complicated by the prior question of the content of modal claims, and in particular about whether they quantify over non-actual possible worlds. Whereas there is little dispute about the initial semantic analysis of mathematical claims—they purport to refer to abstract numbers, sets, functions and so on—there is somewhat less unanimity about the possible worlds analysis of modal claims (Nolan 2011b).