 Metaphysical theories often rely on resources which are taken as “primitive”: roughly, theoretical resources which are not to be further explained or analysed. Different theories of the same subject matter will often take different resources to be primitive, and while it is a difficult question to decide whether one set of primitives is better or worse than another, evaluation of the relative simplicity, naturalness, or other merits of theoretical primitives is part of the evaluation of rival theories. This sort of comparison can can be especially relevant in areas where disputes between rival theories are not to be settled easily by experiment or observation. Such disputes make up one of the battlegrounds between fictionalists and their rivals, with anti-fictionalists claiming that the unanalysed theoretical resources which fictionalists rely on render fictionalist theories unattractive, or at least relatively unattractive compared to some rival or other.