 There is actually a variety of classical indispensability arguments (see Colyvan 2001 and Panza and Sereni 2016) but the general structure of the argument runs as follows. One begins with the premise that mathematics is indispensable for our best science. But, second premise, we ought to believe our best theories. Thus, we ought to be committed to the kind of entities that our best theories quantify over. In general this is an argument in favor of Platonism, as our best science quantifies over mathematical entities.