Monday, August 17, 2009

An argument for semantic externalism

I am not actually convinced by this argument. But let's go.

  1. If it is possible that whether an utterance expresses a proposition depends on what happens at the same time in distant places in the universe, then semantic externalism is true.
  2. It is possible that whether an utterance expresses a proposition depends on what happens at the same time in distant places in the universe.
  3. Therefore, semantic externalism is true.
I am not going to defend (1). It's fairly plausible, though I think it's actually a weak point. I want to defend (2). Suppose Fred and Janine are in distant places in the universe, and speak simultaneously. Fred says:
  1. The sentence Janine is now uttering is true.
Janine says:
  1. The sentence Fred is now uttering is not true.
It cannot be that both of Janine's and Fred's utterances succeed in expressing a proposition. For if they do, then if what Janine says is true, it is not true, and if what Janine says is not true, it is true, which is a contradiction. But in a world where Fred instead says:
  1. 2+2=5.
and Janine still says (5), what Janine utters does express a proposition—indeed, a true one. And in a world where Fred still says (4) but Janine says (6), Fred's utterance expresses a false proposition. So it must be that whether Janine's utterance expresses a proposition depends on what Fred says far away, or that whether Fred's utterance expresses a proposition depends on what Janine says far away. Either option is sufficient to yield (1).

2 comments:

David Gawthorne said...

Saying that a sentence does not express a proposition just because it results in truth value gluts would be seen as an ad hoc move by a dialetheist. Maybe that's the problem.

Alexander R Pruss said...

Sure, but it seems perfectly legitimate to assume classical logic when giving an argument for semantic externalism (or for anything else), except perhaps when arguing directly against a non-classical logician.