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I came across some Substack comments trashing the Twin-Earth thought experiments. The criticisms aren’t new: Chomsky, Dennett, and others thought that Twin-Earth arguments for content externalism are inconclusive for a particular reason.
Truth: their objection sucked. And they should have known it from the very beginning.
According to them, there is no answer to the question ‘Does the protagonist of the thought experiment believe that P?’ Call this the Indeterminacy objection. If this objection is correct, then the thought experiments have much less significance than one would judge from the volume of work written on them.
In this essay I will make three points.
First, it is easy-peasy to fiddle with the thought experiments (both the Putnam “natural kind” ones and the Burge “social” ones) so that the Indeterminacy objection is completely avoided.
Second, when so revised the thought experiments dodge some difficult and popular objections to the thought experiments (e.g., is XYZ really a kind of water?).
Third, Putnam solved this problem in his original work on the topic, some fifty years ago; so there never was any excuse for Chomsky, Dennett, or anyone else to advocate the Indeterminacy objection or make the bad objections.
As things actually stand, in our (real) world, the terms ‘walleye’ and ‘sauger’ each stand for a common North American game fish. You can trust me on this fact, as my father fished quite a bit, caught lots of both kinds of fish, which are of course not the same, and told me about his fishing adventures. The two fish are similar to the eye, just like gold and “fool’s gold”. Only an expert can tell the two kinds of fish apart. The scales are slightly different and the biggest walleye get significantly bigger than the biggest sauger.
Now imagine an alternative situation in which ‘walleye’ and ‘sauger’ are switched in meaning. In this imaginary world ‘walleye’ is used to pick out sauger fish and ‘sauger’ is used to pick out walleye fish. So when someone in that world utters ‘Walleye are big’ she has really said that sauger are big.
In this imaginary world my father Ron read an article in an authoritative fishing magazine that contained the sentence ‘Walleye get bigger than sauger’. Clearly, what that sentence means in that world is that sauger get bigger than walleye (because the meanings of ‘walleye’ and ‘sauger’ are switched in that imaginary situation). When the author wrote ‘Walleye get bigger than sauger’, she was expressing the idea that sauger get bigger than walleye. This is uncontroversial. She was expressing a false idea, but it’s an idea all the same. Suppose also that Ron believed what the article said. So he believed what the author said, namely that sauger get bigger than walleye—although he expressed his belief the same way as the author did, with the sentence ‘Walleye get bigger than sauger’.
In this fantasy world Ron tells me his opinion. He says to me ‘Walleye get bigger than sauger’, thereby echoing the fishing article author. As before, what he means with that sentence is that sauger get bigger than walleye. That’s what he and the author believe—that sauger get bigger than walleye.
Let’s say that in that world I am agreeable about such matters, and so I take my father at his word. That is, I come to accept his belief. Like him, I believe that sauger get bigger than walleye and I express this belief just like everyone else does, with the sentence ‘Walleye get bigger than sauger’.
In this imaginary scenario I can’t tell walleye and sauger apart—at least on my own. If you put them in front of me but not allow me to use other people, books, articles, and other sources of information, then I cannot confidently tell you which is which. But of course that doesn’t mean I could never tell them apart at all. I could easily learn about the difference in scales. Or ask an expert. The same actually holds for my individualistic discriminatory abilities vis-à-vis Pepsi and Coke. I can’t tell them apart if you leave me on my own and take off the labels. But I have lots of ordinary Pepsi and Coke beliefs. Individualistic discriminatory abilities are not worth much.
Now let us leave the realm of imagination and return to the real world. A few decades ago when I lived in Minnesota Ron actually told me that walleye get bigger than sauger. And since the only language he knows is English, he used the sentence that actually expresses that idea—the sentence ‘Walleye get bigger than sauger’. As things actually stand today, I firmly believe that walleye get bigger than sauger.
So in the two worlds I believe different things. That’s because it’s plain as day that the belief that sauger get bigger than walleye—my imaginary belief—is distinct from my belief that walleye get bigger than sauger—my actual belief. One belief is the reverse of the other. And of course there is no reason to think that I have both beliefs in both worlds. There may be all sorts of cases in which people rationally hold contradictory beliefs (maybe Lois Lane), but this isn’t one of those cases.
Now comes the clincher: there’s nothing preventing me from being physically identical in the two worlds. For instance, I need never see, smell, or touch either fish, so my experiences with the fish themselves can be identical (since there are none). In addition, my fishing conversations with my father can be exactly the same physically. For instance:
Me: “Dad, which fish gets bigger?”
Ron: “Walleye get bigger than sauger!”
Me: “Okay. Whatever you say. Walleye get bigger than sauger.”
Although I hear the same words (or word-forms) from my father in the real and fantasy worlds, I acquire different beliefs—his beliefs. In fact, all my encounters with ‘walleye’ and ‘sauger’ can be identical in the two worlds.
Although in the actual world I believe that walleye get bigger than sauger, in the counterfactual world I believe that sauger get bigger than walleye. In the actual world my belief is true whereas in the counterfactual world my belief is false—even though the things the beliefs are about (the two kinds of fish) are identical in the two worlds. Hence, any theory that tries to understand a thought’s truth conditions internally, from the skin in, is doomed to fail. When it comes to ordinary truth-conditional content, I differ across worlds.
We can do the same thing for Burge “social externalist” arguments. As I understand it, a heart attack is stipulatively defined as the death of heart-muscle cells from reduced or obstructed blood flow through the coronary arteries. In any case, we can easily imagine a world in which there are these medical definitions. Heart attacks are usually caused by blockage of coronary arteries by a blood clot, spasm or contracture; or a severe disruption in the heart’s rhythm.
A stroke is stipulatively defined as a sudden decrease in the blood supply to part of the brain, damaging the area so it cannot function normally. Hardening of the arteries or high blood pressure are the usual causes of strokes. Most people, at least adolescents who have thus far been removed from people suffering strokes and heart attacks, are not aware of these definitions, although they know that both problems have to do with the heart and are quite serious. In fact, most people have no idea that there are such “definitions”.
Jazmine knows that her Uncle Fred had a heart attack many years ago, that her great-grandmother Ester died of a stroke, etc. And on the basis of the testimony of her trusted friend Reggie, she believes that strokes are more serious than heart attacks.
Now consider a world in which the terms ‘stroke’ and ‘heart attack’ have switched definitions. Suppose further that in that world Fred had not a heart attack but a stroke and Ester died of not a stroke but a heart attack. Finally, suppose that Reggie had come to the reverse opinion, that heart attacks are more serious than strokes—although of course she expressed her opinion with ‘Strokes are more serious than heart attacks’. So Jazmine hears all the same sentences involving ‘stroke’ and ‘heart attack’ in each world. But she obtains different beliefs in the two worlds (just like Reggie): in the actual world she believes that strokes are more serious than heart attacks whereas in the counterfactual world she believes that heart attacks are more serious than strokes. I’m not going to do it here, but it should be plain that it does not take much imagination to elaborate on the thought experiment to make it as realistic as you like.
I’m not defending either of those thought experiments. My first two goals are to show that (a) the thought experiments can easily dodge the Indeterminacy objection, and (b) while the question ‘Why isn’t XYZ a kind of water?’ is a good one, it’s irrelevant to the Twin-Earth argument template. As for my third thesis, consider what Putnam wrote 1975: “[J]ust let the words ‘elm’ and ‘beech’ be switched on Twin Earth (the way ‘aluminum’ and ‘molybdenum’ were in the previous example)” (1975, 227). It was all there in 1975 folks!
I hope that the foregoing removes the Indeterminacy objection from our thoughts, shows how some objections (e.g., the one about XYZ being a kind of water) are irrelevant, and rekindles our admiration of Putnam’s work.
Chomsky, Noam (2000). New Horizons in the Study of Language and Mind (Cambridge: Cambridge University Press).
Dennett, Daniel (1982). “Beyond Belief,” in Woodfield, ed. Thought and Object (New York: Oxford University Press).
Dennett, Daniel (1996). “Cow-sharks, Magnets, and Swampman,” Mind and Language, v.11 n.1: 76-77.
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