July 11, 2021

## Against semantic externalism

Sometime, I think it was back in the 1990s, I was involved in an online discussion of AI. I casually remarked that meanings are subjective. To my surprise, somebody gave me an argument against that. The basic idea was that language is shared in the community, and therefore meanings must be shared, so could not be subjective.

I remained unpersuaded, so I was pointed to Hilary Putnam’s paper “The meaning of ‘meaning'”, where Putnam argues that “meaning is not in the head.”

This post is about why I disagree. The expression “semantic externalism” is commonly used for the view expressed by Putnam and others, that meaning comes from the community rather than from the individual person.

## Experience

My own experience suggests that people disagree a lot about meanings. They perhaps believe that they are disagreeing about logic or about evidence, but often the real disagreement is about meanings. That’s where I get the idea that meanings are subjective. As an example, look at arguments about “free will”, where disagreements over whether we have free will often look more like disagreements over what we mean by “free will”.

Of course, it is quite possible — and even likely — that what I mean by “meaning” is not the same as what Putnam means by “meaning”. But, if that is the case, then our own disagreement about the meaning of “meaning” is evidence that meaning is subjective.

## Twin Earth

In his argument, Putnam introduces the idea of “Twin Earth”. Here, Twin Earth is a planet much like earth, with similar people. And what’s in the heads of Twin Earthians is said to be the same as what’s in the heads of us earth people. But, on Twin Earth, the liquid that they call “water” actually has a chemical composition of $XYZ$ instead of $H_2O$. Yet the Twin Earthians talk about it as “water” much as we would for $H_2O$.