 There are a few different ways that platonists might try to argue against fictionalism. The most famous and widely discussed argument against fictionalism is the Quine-Putnam indispensability argument (see Quine (1948, 1951), Putnam (1971, 2012), and Colyvan (2001)). This argument (or at any rate, one version of it) proceeds as follows: it cannot be that mathematics is untrue, as fictionalists suggest, because (a) mathematics is an indispensable part of our physical theories (e.g., quantum mechanics, general relativity theory, evolutionary theory, and so on) and so (b) if we want to maintain that our physical theories are true (and surely we do — we don't want our disbelief in abstract objects to force us to be anti-realists about natural science), then we have to maintain that our mathematical theories are true.