 Third, and finally, there is an important divide between models of reference which are expansive as opposed to narrow. In their broadest forms, both intentionalism and descriptivism are expansive; they purport to apply equally well to any sort of referential term whatsoever. The causal model is a narrow model of reference; it has only ever been purported to apply to the reference of names. Once more, the character model proves difficult to place; just how broad or narrow it proves will depend on just how far we are willing to stray in our theorizing from the paradigm case of the true indexicals. Expansive theories hold out the promise of offering a substantive account of the reference relation. That is, expansive theorists can claim that the reason that token uses of referential terms play a certain sort of role in explaining the the truth or  falsity of an utterance is that a certain sort of substantive relation obtains between that token use and some object in the world. Narrow theorists, in contrast, will have to allow that there are different sorts of relations that serve to fix reference for different sorts of referential terms, and even perhaps different uses of the same term. Thus, they will have to say that what unifies referential terms is not that, when they succeed in referring, a particular sort of relation obtains between that token use and some object or individual, but rather that they play some particular functional role in determining the truth-conditions or assertive content of an utterance. In other words, standing behind debates over which of these models we should adopt is a much larger, and as yet unresolved, question: just what are our explanatory ambitions in offering a theory of reference in the first place?