 By far the most important and widely discussed argument against fictionalism is what’s known as the Quine-Putnam indispensability argument (see, e.g., Quine (1948, 1951), Putnam (1971), Resnik (1997), and Colyvan (2001)). This argument has been formulated in a number of different ways. One very simple version of the argument can be put like this: (i) mathematical sentences form an indispensable part of our empirical theories of the physical world—i.e., our theories of physics, chemistry, and so on; (ii) we have good reasons for thinking that these empirical theories are true, i.e., that they give us accurate pictures of the world; therefore, (iii) we have good reasons to think that our mathematical sentences are true and, hence, that fictionalism is false.