Bridging syntax and semantics with Quine's Gavagai

by Stuart_Armstrong 1 min read24th Sep 20182 comments


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Crossposted from the AI Alignment Forum. May contain more technical jargon than usual.

Quine has an argument showing that you can never be sure what words mean in a foreign language:

Quine uses the example of the word "gavagai" uttered by a native speaker of the unknown language Arunta upon seeing a rabbit. A speaker of English could do what seems natural and translate this as "Lo, a rabbit." But other translations would be compatible with all the evidence he has: "Lo, food"; "Let's go hunting"; "There will be a storm tonight" (these natives may be superstitious); "Lo, a momentary rabbit-stage"; "Lo, an undetached rabbit-part." Some of these might become less likely – that is, become more unwieldy hypotheses – in the light of subsequent observation.

What does this mean from the perspective of empirically bridging syntax and semantics?

Well, there is no real problem with "gavagai" from the empirical perspective; the fact that there seems to be one is, in my view, due to the fact that the syntax-semantic discussion has focused too heavily on the linguistic aspects of the problem.

Let be the symbol in the Arunta speaker's brain that activates when they say "gavagai". As Quine said towards the end of his quote, "some of these might become less likely – that is, become more unwieldy hypotheses – in the light of subsequent observation." Relatedly, Nick Bostrom argues that indeterminancy is a "matter of degree".

In practice, this means is that if, for instance, r="A rabbit is there" and s="A storm is coming tonight", then, if we accumulate enough observations, the is going to be predictive of better than it is of , or vice versa. Thus there is an empirical test for whether corresponds to some of these hypotheses.

But what about u="An undetached rabbit-part is there"? It may be very difficult to find a situation that distinguishes between u and r in practice - so does stand for "rabbit", or "undetached rabbit-part"?

Similarly to the example of the neural net in the previous post, is a symbol for both r and u. If no experiment can distinguish between the two - or, at least, if no experiment can distinguish between the two in any typical environment that any Arunta speaker would ever experience - then they are synonymous (or, equivalently, they are strongly within each other's web of connotations).

If we presented the speaker with a situation far outside their typical environment, then we might be able to distinguish r from u - but we'd be uncertain if 'meant that all along', or if the speaker was extending the definition to a new situation.

Back to linguistics

There are some ways we might be able to distinguish whether "gavagai" means "rabbit" or "undetached rabbit-part", even if u and r cannot be distinguished in practice. It's plausible that there might be an internal variable in the speaker that corresponds to "part of an animal", and an internal that correponds to "undetached" (versus detached).

Then, when is activated, we might ask whether and are also activated, or not. You can see this as the internal web of connotations amongst the variables in the human brain. It seems people with different languages have different internal webs, different ways of connecting words and concepts together.

This does not, however, affect the connection between and external variables.


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