  Another common and widely discussed argument against abstract objects is an epistemological argument. The argument is grounded in the thought that given that abstract objects are causally inert, it is difficult to understand how we can have knowledge or reliable belief about them. Sometimes a similar argument is advanced according to which the problem with Platonism is that, given the causal inertness of abstract objects, it cannot explain how linguistic or mental reference to abstract objects is possible (see Benacerraf 1973 and Field 1989, 25–7). Admittedly these arguments do not conclusively establish Nominalism but, if they work, they show an explanatory lacuna in Platonism. The challenge for the Platonist is to explain how knowledge of and reference to abstract objects is possible. Most of the debate with respect to this argument has concentrated on the particular application of the argument to the case of mathematical objects (for more on this debate see the entry on  Platonism in metaphysics   and Burgess and Rosen 1997, pp. 35–60.)