 There are two standard problems for causal theories of this sort (whether they are elaborated in a mentalist or a non-mentalist way). The first is the problem of extending the theory from the case of names to to other sorts of vocabulary for which the theory seems less natural. Examples which have seemed to many to be problematic are empty names and non-referring theoretical terms, logical vocabulary, and predicates which, because their content does not seem closely related to the properties represented in perceptual experience, are not intuitively linked to any initial act of “baptism”. The second problem, which is sometimes called the “qua problem”, is the problem of explaining which of the many causes of a term’s introduction should determine its content. Suppose that the term “water” was introduced in the presence of a body of H2O. What made it a term for this substance, rather than for liquid in general, or colorless liquid, or colorless liquid in the region of the term's introduction? The proponent of a causal theory owes some answer to this question; see for discussion Devitt and Sterelny (1987).