Various forms of “pluralism” are making the rounds these days. There is, for instance, the “logical pluralism” of Beall and Restall (among others), the subject of a recent book by Stewart Shapiro, which will be discussed here at some point. But then there is also something much vaguer and murkier called “ontological pluralism,” which, amazingly, is attributed to Carnap. Matti Eklund, for instance, considers this question in his paper in the Metametaphysics volume. What does he mean by it? He considers various formulations, starting with the “quantifier-variance” understanding of Hirsch, in which ontological pluralism requires the quantifiers to take on different interpretations in different languages. But Eklund thinks this is insufficiently precise, as it can seem to amount to “the thesis that a string of symbols can come out true in some languages but false in others, while meaning what it actually means.” The trouble with this, he thinks, is that it “would appear to commit the ontological pluralist to a form of relativism or idealism absent from pluralist writings.” (p. 138)
The quantifier-variance interpretation of Carnap doesn’t get off the ground, though, because Carnap does not see the quantifiers in the different possible external statements as having different interpretations; he sees them as having no interpretation at all. This also extinguishes Eklund’s further worry, quoted at the end of the above paragraph, since Carnap did not think truth or falsehood had any application in external discourse; they could be applied only with respect to an explicitly specified descriptive language. And what a sentence “actually means” is of course entirely language-relative. So it is not “the same sentence” in different languages. A “string of symbols” cannot “come out true in some languages but false in others, while meaning what it actually means,” because “what it actually means” is not specifiable language-independently. To suppose that a string of symbols “actually” means something independently of the language it is expressed in is just to take an external statement literally, at face value.
To even consider attributing this to Carnap betrays a failure to grasp the most fundamental feature of Carnap’s later philosophy, i.e. the specifically Carnapian linguistic turn I’ve discussed elsewhere. Fans of ontology should by all means go off into their ivory-tower “ontology room” and study “ontological pluralism” to their heart’s content. But could they please stop associating it in any way with Carnap?