Unicorns and error theory

Kripke famously argued that unicorns cannot exist. For “unicorn” would have to refer to a natural kind. But there are multiple non-actual natural kinds to which “unicorn” could equally well refer, since it’s easy to imagine worlds w₁ and w₂ in each of which there is a natural kind of animal that matches the paradigmatic descriptions of unicorns in our fiction, but where the single-horned equines of w₁ are a different natural kind (at the relevant taxonomic level) from the single-horned equines of w₂. The proposition p expressed by “There are unicorns” is true in one of the worlds but not the other, or in both, or in neither. Symmetry rules out its being true in one but not the other. It can’t be true in both, because then “unicorn” would refer to two natural kinds (at the relevant taxonomic level), while it arguably refers to one (at least if we index it to a sufficiently specific body of fictional work). So, the proposition must be true in neither world, and by the same token, there will be no world where it’s true.

It seems to me, however, that rather than saying that the proposition expressed by “There are unicorns” is impossible, we should say that “There are unicorns” fails to express a proposition. Here’s why. We could imagine Rowling enriching the Harry Potter stories by introducing a new species of animals, the monokeratines. Suppose she never gives us enough detail to tell the two species apart, so all the descriptions of “unicorns” in her stories apply to “monokeratines” and vice versa, but she is clear that they are different species (perhaps the story hinges on one of them being an endangered species and the other not).

Now, if “There are unicorns” in these (hypothetical) stories expresses a proposition, so does “There are monokeratines”. But if they express propositions, they express different propositions (neither entails the other, for instance). Thus, suppose “There are unicorns” expresses p while “There are monokeratines” expresses q. But no reason can be given for why it’s not the other way around—why “There are unicorns” doesn’t express q while “There are monokeratines” expresses p. In fact, the exact same reasoning why Kripke rejected the hypothesis that “There are unicorns” is true in one of w₁ and w₂ but not in the other applies here. Thus, we should reject the claim that either sentence expresses a proposition.

But if we do that, then we should likewise reject the claim that in the actual world, where Rowling doesn’t talk about monokeratines, “There are unicorns” expresses p (say). For it could equally well express q.

Maybe.

But maybe there is another way. One could say that “There are unicorns” is vague, and handle the vagueness in a supervaluationist way. There are infinitely many species u such that “There are unicorns” can be taken to be precisified into expressing the proposition that there are us. Thus, there is no one proposition expressed by the sentence, but there are infinitely many propositions for each of which it is vaguely true that the sentence expresses it.

This might be a good response to my old argument that error theorists should say that “Murder is wrong” is nonsense. Maybe error theorists can say that “Murder is wrong” has infinitely many precisifications, but each one is false, just as “There are unicorns” has infinitely many precisifications, but each one is false.

This suggests a view of fiction on which claims about fictional entities always suffer from vagueness.

An interesting thing is that on this approach, we need to distinguish between in-story and out-of-story vagueness. Suppose a Rowling has a character say “There are unicorns.” In-story, that statement is not vague. I.e., according to the story there is a specific species to which the word “unicorn” as spoken by the character definitely refers. But out-of-story, we have vagueness: there are infinitely many possible species the claim could be about.

This suggests that the error theorist who takes the vagueness way out is not home free. For it is a part of our usage of “(morally) wrong” that it refers fairly unambiguously to one important property. But the error theorist claims vagueness. If the statements about wrongness were made in a story, then the error theorist could handle this by distinguishing in-story and out-of-story vagueness. But this distinction is not available here.

A similar problem occurs for a real-world person who claims that there are unicorns. Maybe one could say that the person intends in saying “There are unicorns” to express a single specific proposition, but fails, and vaguely expresses each of an infinity of propositions, all of them false. If so, then a similar move would be available to the error theorist. But I am sceptical of this move. I wonder if it’s not better to just say that “There are unicorns” as said by someone who intended to express an existential claim about a single definite species is nonsense, but there is a neighboring sentence, such as “There is an extant species of single-horned equines”, that makes sense and is true.