 The contents of mental representations are typically taken to be abstract objects (properties, relations, propositions, sets, etc.). A pressing question, especially for the naturalist, is how mental representations come to have their contents. Here the issue is not how to naturalize content (abstract objects can’t be naturalized), but, rather, how to specify naturalistic content-determining relations between mental representations and the abstract objects they express. There are two basic types of contemporary naturalistic theories of content-determination and causal-informational and  functional.[3]