Thursday, April 25, 2013

The possibility of unicorns

Kripke argued that it is not possible for there to be unicorns. For "unicorn" is a natural kind term. But there are many possible natural kinds of single-horned equines that match our unicorn stories, and there is no possible natural kind that has significantly more right to count as the kind unicorn. So none of them count, and no possible world contains unicorns.

But there is another approach, through vagueness and supervaluationism. Let's say that the term "unicorn" is vague. It can be precisified as a full description of any one of the possible natural kinds of single-horned equines that match our unicorn stories.

Now consider the sentence that Kripke is unwilling to assert but which seems intuitively correct:

  1. Possibly there is a unicorn.
We get to say (1) if we can correctly affirm:
  1. Definitely, possibly there is a unicorn.
And we certainly do get to say this. For (2) holds if and only if:
  1. For every precification U of "unicorn", possibly there is a U.
And assuming that all the precifications of "unicorn" are natural kinds that are possibly instantiated (we don't allow as a precification of "unicorn" something whose eyes are square circles, etc.), (3) is true. And so even if there is no world at which definitely there is a unicorn (though there might be—maybe that world is very rich and contains animals that fall under all possible precifications of "unicorn"; Blake McAllister suggests a multiverse), it is definite that there is a world at which there is a unicorn.


Unknown said...
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Dagmara Lizlovs said...

I don't recall ever seeing a one horned equine. The equines I've dealt with always needed to have a good set of horns to keep their halos secure and set straight. My Thoroughbred, Merlin, was especially like this. I liked him when he was good, but I really loved him when he was bad. I once put a fly bonnet on his head, and the way this particular fly bonnet covered his ears made him look like he had devil horns. I had one good look at him and said "How becoming."

Then when it comes to unicorns, you might want to check this one horned deer out:

Unknown said...

I think I've found six premises Kripke might approve and which entail that necessarily there are no unicorns:

P1. Necessarily, for any natural kind, if it is the 'unicorn' kind, then necessarily (it is the 'unicorn' kind if it exists).
P2. Necessarily, the 'unicorn' kind (if there is one) is a 'one-horned equine' kind.
P3. Necessarily, for any 'one-horned equine' kind x, possibly there is also another 'one-horned equine' kind that has at least as much right to be the 'unicorn' kind as x does.
P4. Necessarily, if there is a 'unicorn' kind, then it has more right to be the 'unicorn' kind than does anything else.
P5. 'Unicorn' is a natural kind term.
P6. For any F, if "F" is a natural kind term, then necessarily there is an 'F' natural kind if there are any F's.

Is Pruss objecting to the first premise? (I tend to reject P3 or P5.)

Alexander R Pruss said...

On the vagueness take, "the 'unicorn' kind" is vague. Premises 1, 2, 4 and 5 are all definitely true. But premise 3 is definitely false--for every disambiguation of "the 'unicorn' kind" it is false.

Unknown said...

Gotcha. Thanks for that explanation.