 Quite apart from positive motivations for antirealism, fictionalism is also of relevance for evaluating particular arguments for realism. Let me discuss two. (a) What we may call ordinary language arguments. An ordinary language argument for the existence of Fs goes as follows. “(1) Sentences thus-and-such are true. (2) (Semantic analysis shows that) for those sentences to be true, there must be Fs. (3) So, there must be Fs.” An argument of this form is clearly valid. The question of the soundness of an argument of this kind comes down to whether the premises are true. Hermeneutic fictionalism presents problems for the justification of premise (1). Maybe all that is evident from ordinary discourse is that we somehow convey or communicate true propositions when uttering the relevant sentences. But hermeneutic fictionalism indicates how we can do so without the sentences semantically expressing true propositions. Thomasson (2013) is a recent extended discussion of the relation between fictionalism and her own preferred ontological view, which is argued for by what she calls “easy arguments”, a kind of ordinary language arguments. Thomasson’s ontological deflationism says, roughly, that all manners of philosophically controversial entities exist, and do so in some sense trivially. The way Thomasson presents things, fictionalism and ontological deflationism are in conflict. But if fictionalism is only a linguistic thesis (compare the distinction between the ontological thesis and the linguistic thesis) — and that is how Thomasson appears to understand it — that’s not quite true. What is true is that fictionalism presents problems for Thomasson’s specific way of arguing for ontological deflationism, by appeal to ordinary language arguments. (b) Indispensability. Let us again take mathematics as our example. One of the most influential arguments for platonism in the philosophy of mathematics is the indispensability argument, according to which quantification over mathematical entities is indispensable to our best theory of the world, and hence we should take mathematical entities to exist. (This is a very rough characterization of indispensability arguments. For more detail see the entry on  indispensability arguments in the philosophy of mathematics.)  But revolutionary fictionalism suggests a complication: even if, in some sense, quantification over mathematical entities is indispensable to our best theory of the world, perhaps it is not literal quantification over mathematical entities that is thus indispensable. The relation between hermeneutic fictionalism and indispensability arguments is a bit more indirect. But hermeneutic fictionalism is relevant to indispensability arguments insofar as it is analyses of what scientists of various stripes actually say and believe that tell us what is “our best theory of the world”. 