In the twin Earth thought experiment Putnam determines that meanings are not in the head. Later interpretations, by himself and by others, take it to falsify functionalism.

It seems to me that the argument can't disprove functionalism, and even that it might even entail that functionalism is true:

(1) I take it that when I say "water" or "gold" I don't fully understand the term, and that it's determined by the physical and the social surrounding. Yet, part of it I do understand, and hence while I say "water" I am in a functional state of believing that I see water to the extent that my knowledge allows me. I am in some kind of a state - that can be (potentially) explained in computational terms - even though I don't grasp the full meaning of water. "Water" has meaning in my head, definitely, but it's not the most precise one. it's narrow (as Block calls it), while the full meaning is wide. In other words, when I think of "water" (H2O) and when my twin on twin earth thinks of "water" (XYZ) we are both in the same mental state, and this fact cannot say anything to falsify functionalism. What is wrong with that (very simple) answer to Putnam?

I can rewrite this question in terms that I believe are equivalent (though I might be wrong, and this might be my problem to understand). Putnam says that while talking about indexicals ("I", "That", "now") - intention doesn't determine extension. It seems right, because when I say "I" and when you say "I" - we both have the same intention (meaning), but the extension (what we refer to) is different. My "I" is me while your "I" is you. If we take this to other terms, like natural kinds, we have no problem. My "water" (H2O) and your "water" (XYZ) have different extensions, and yet the meaning of "water" for you and the meaning of "water" for me is the same. Hence - when we both say water, we are in the same state. Intention doesn't determine extension, I take it, but intention itself is only a concept, and therefore a mental state. functionalism still works. It seems like for some reason Putnam doesn't want to take the indexicals case onto the other terms case (I can't see why). If we follow him, I don't understand the picture we can derive.

(2) Assuming (1) is explained, and meanings are not in the head. Now, as I see it - the problem with functionalism is that we cannot see how a computer program creates real meaning. Algorithms can be interpreted in various ways. As long as the machine is concerned - it only manipulates symbols. We, being external to the machine, interpret it's result and give it a meaning. According to this, machines cannot create genuine meaning, while it feels like we, humans, can. In other words, machines have only derived meanings, while we have original meanings. But then comes Putnam and says that the meanings we humans have are not really in the head, but are meaningful only external to us. It seems like a good solution for the problem with functionalism just described. A machine cannot have a genuine meaning, but it's not a problem after Putnam, because also humans cannot. Meaning is always external (and hence always derived), and hence we can definitely be described computationally.

I assume that my understanding of Putnam isn't complete, but I can't see how my claims above won't hold.

  • welcome to Phil.SE! It might be worth adding a link to the Putnams Twin Earth argument; I'm not familiar with it, nor have I come across it even in name; adding explanatory detail might help in attracting good answers. Jul 17, 2015 at 11:02
  • I didn't know the argument could be used against functionalism in philosophy of mind. It seems dubious to me that a semantic argument could have metaphysical consequences. Do you have any reference? Isn't it rather a functional conception of meaning that is refuted? Jul 17, 2015 at 12:53
  • Putnam himself uses this argument against functionalism in "Why Functionalism Didn't Work" (1992b)
    – Amit Hagin
    Jul 17, 2015 at 13:05
  • Thanks for the reference. The text is not available online. Your argument seems sound, hard to answer without having putnam's argument in detail. Maybe ask him the question on his blog? ;-) Jul 18, 2015 at 4:50

3 Answers 3


The Twin Earth argument undercuts functionalism because it undercuts the identification of the mental with the functional. But the problem is not with creating "meanings", but with capturing them faithfully. It is worth recalling that Putnam was a champion of computational functionalism back in 1960s, before he wasn't. According to functionalism human mind is represented by a finite automaton running instructions of the kind:"given input I in state S change state to S' and produce output O". States are symbolic codes, and like any syntactic system this one is multiply interpretable, so it can not pick out unique "meaning" of mental states, i.e. their "intentional objects" (this is the price of "implementation neutrality" of functionalism). Putnam originally sought to fix the interpretation by requiring physical specificity of input/output.

This is where Twin Earth comes in. Oscar and Toscar are functionally equivalent, have identical physical input/output because the action takes place before 1750 and they have no way of distinguishing between H20 and XYZ, but their "meanings" of "water" are different, because one is H20 and the other is XYZ. This is because Putnam dismisses the Frege-Russell descriptivist theory of meaning as inadequate, and adopts Kripke's rigid designation. Thereby "meaning" is fixed in the act of naming, can be outsourced to "experts" through "linguistic division of labor", and is "sensitive to future discovery" through "communal chain of referential transmission". In other words, although Oscar and Toscar can not distinguish between water and twater, they know that others know (or will know) how to tell the difference, and that distinguishes their meanings. Putnam also gives example of himself not being able to tell the difference between elms and beeches but having distinct meanings of them by outsourcing reference to experts.

"The Twin Earth argument created a strom in philosophical community reviving the view called psychological externalism, on which some determinants of mental content are located in the speaker's environment".

Some fixes were tried, but the Twin Earth problem is relatively minor for functionalism compared to the implementation problem. Putnam himself later discovered that automata functionally equivalent to humans can be implemented by rocks, and that humans can implement hundreds of inequivalent automata at the same time. All of those would have to be assigned "mental states" under computational functionalism.

"Putnam himself, having advanced powerful arguments against the very doctrine he had previously championed, is largely responsible for its demise. Today, Putnam has little patience for either computational functionalism or its underlying philosophical agenda. Echoing despair of naturalism, Putnam dismisses computational functionalism as a utopian enterprise".

See Rise and Fall of Computational Functionalism (pp.16-20) paper for more details on functionalism and Twin Earth, and Realism, Reference, & Possible Worlds: the Approach via Modal Logic on its relation to rigid designation.

  • Thanks for the answer. It does make things clear, and the references are good. Still, I don't understand why can't we just say that two people have the same concept when are in the same state, but concept doesn't determine extension. If we say so, Oscar and Toscar are in the same state, have the same meaning while saying "water", but the reference is different. Meaning, under this interpretation, is only in the head.
    – Amit Hagin
    Jul 19, 2015 at 9:13
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    @nir, I think that Dennett's laboratory assumes the truth of functionalism. But anyway, this idea emphasizes the problem I have with the argument. Why can't we say that both identical brains are in the same state and therefore have the same concept (meaning) when they say "water", even though one is in the presence of H2O and the other is in the presence of XYZ? Why can't we just give up the idea that concept determines extension in order to keep the idea that a mental state determines concept?
    – Amit Hagin
    Jul 20, 2015 at 9:37
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    @Amit Hagin This would take us back to descriptivism. Why Putnam and others rejects it is a separate issue that ties into broader issues, Norris discusses some in the linked paper. They want "scientific meaning" that "tracks reality" and doesn't shift every time a major discovery is made, feeding into "incommensurable paradigms" of Kuhn, cultural relativism and antirealism.
    – Conifold
    Jul 20, 2015 at 19:40
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    @Amit Hagin They also want recognition of the social nature of knowledge and meaning, which descriptivism reduces to atomic individuals. Under descriptivism even the modern meaning of "water" is totally different from the one before 1750 and varies from person to person, they want a notion robust across individuals and time. So to Putnam different referents are not enough, Oscar and Toscar really "mean" differently, and if functionalism can not reflect that so much the worse for functionalism.
    – Conifold
    Jul 20, 2015 at 19:41
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    @Ram, (and Conifold) Putnam himself writes that with indexical he'd prefer this option: I say "I", and you say "I", and we both mean the same (we have the same idea of "I"). The reference of our "I" is different. My "I" is me and your "I" is you. It has nothing to do with the fact that we are in the same state. Why can't we say the exact same thing about water - we mean the same, but the reference is different?
    – Amit Hagin
    Jul 21, 2015 at 11:52

I will focus here on the first part of the question, which pertains to Putnam's argument to the effect that "meanings ain't in the head". I take this (rather than functionalism) to be the main issue.

Putnam says that while talking about indexicals ("I", "That", "now") - intention doesn't determine extension. It seems right, because when I say "I" and when you say "I" - we both have the same intention (meaning), but the extension (what we refer to) is different. My "I" is me while your "I" is you. If we take this to other terms, like natural kinds, we have no problem. My "water" (H2O) and your "water" (XYZ) have different extensions, and yet the meaning of "water" for you and the meaning of "water" for me is the same . . . It seems like for some reason Putnam doesn't want to take the indexicals case onto the other terms case (I can't see why). If we follow him, I don't understand the picture we can derive.

Putnam, partly by intention, began his argument with a hazy notion of 'meaning'. The stated goal of his famous essay ("the meaning of meaning" (1975)) was to offer a new account of meaning. Part of that haziness was in the notion of intension. Putnam introduced the distinction between extension and intension through this example: the expressions "creature with heart" and "creature with kidney" have the same extension, yet they differ in "meaning", in some sense of that term. The sense of "meaning" in which the two expressions differ, we call 'intension'. Later, Putnam mentions the view, that intension determines extension,  as a "traditional doctrine", without offering any rationale for this view. On the other hand he states that "no one has ever offered" that intension determines extension for indexicals (as  mentioned in the question). These two statements seem to be in conflict. If there is a general, principled doctrine that intension determines extension, how can there be exceptions, like indexicals? Putnam did not engage this problem.

Putnam did make clear, however, in what way natural-kind terms (like water, gold, elm, beech; those that are involved in the "twin earth" thought experiments) are relevantly different than indexicals. The "twin earth" cases demonstrate, according to Putnam, a social aspect in natural-kind terms, that does not exist in indexicals. For example, the meaning of 'gold' for me includes the chemical structure of gold, even though I don't know what that structure is. And at least part of the explanation is that I trust that someones in my larger community, the experts, do know the chemical structure of gold.

This could be taken to also justify Putnam's choice, that with regard to natural-kind terms, meaning (intension) does determine extension. For indexicals it seems that what is "in the head" is insufficient to determine the extension. For natural-kind terms, on the other hand, even though nothing in my head determines then extension, something in someone else's head (the relevant expert) does determine the extension. This seems to give a reason to identify the meaning of my words, not with the contents of my head, but with the content of someone else's head (the expert), which does determine the extension.

Putnam did not take this line of justification, however, for the position that meaning determines extension, for natural-kind terms. Like before, he abstained from providing any principled reasons why meaning should determine extension. Instead, he simply appealed to what he took to be the common use of the word 'meaning':

Consider 'elm' and 'beech', for example. If these are 'switched' on Twin Earth, then surely we would not say that 'elm' has the same meaning on Earth and Twin Earth, even if my Doppelgänger's stereotype of a beech (or an 'elm', as he calls it) is identical with my stereotype of an elm. Rather, we would say that 'elm' in my Doppelgänger's idiolect means beech. For this reason, it seems preferable . . . to identify 'meaning' with an ordered pair . . . of entities, one of which is the extension . . . Doing this makes it trivially true that meaning determines extension . . . my Doppelgänger and I mean something different when we say 'elm', but this will not be an assertion about our psychological states. (Putnam, Mind, Language and Reality p.245)

Putnam then concluded that the problem of meaning splits into two problems: first, the determination of extension, which pertains to meaning in the strict sense of the word, and which involves a social "division of labor". Second, the competence that is required from an individual in order to express meanings. This again involves social ingredients, how an individual hooks into a community in a way that enables one to use many words that, strictly speaking, one understands only superficially.

  • Thanks a lot! That does put things well. Putnam's choice, then, seems "preferable" (even more after Kripke's "naming and necessity"), but he doesn't logically prove it in any sense.
    – Amit Hagin
    Jul 23, 2015 at 18:15
  • @amit Exactly. Putnam's argument certainty did not seal the issue. But it did provoke a lively debate. Jul 23, 2015 at 20:06

Regular earth guy is pointing at a glass of H20

Opposite earth lady points at a glass of XYZ

They both say this is water.

Let us shelve the question of if this is merely a naming issue for now, as well as the question of if things have the same (equal in all regards other than position) properties, they fall under the same class. Though I find these questions highly relevant to philosophy, neither of these debates will help with this thought experiment.

So we have from your question :

I think of "water" (H2O) and when my twin on twin earth thinks of "water" (XYZ) we are both in the same mental state

We will use Reg and Opp to represent the two agents from here out.

and yet the meaning of "water" for you and the meaning of "water" for me is the same.

I will attempt to contest this point under the rules of the thought experiment. I'm assuming when you say "you" you mean a "me" on twin earth.


Hence - when we both say water, we are in the same state.

So Reg says the word water, and his mind is referring to H2O

Opp says water, and his mind is referring to XYZ Their meaning is different

XYZ != H2O

Even though XYZ and H20 have all the same properties (This I think is where the weakness in Putnam's argument really is... but if we diverge here the thought experiment falls apart)

If you have cats that are identical twins, and you name one H20 and one XYZ you can call them the wrong names, and they can even react how you would expect, but your meaning and your reference do not match.

If this makes you change your mind about the meaning being the same then perhaps you could rethink if the thought experiment disproves functionalism. I myself have never read or heard discussion of this particular thought experiment in conjunction with functionalism.

For those that want a quick summary of the original argument

As for how it might be a problem for functionalism, I'd say it is because Opp and Reg have completed the same function with a different intent. However this is not my go to argument against functionalism, and I would not present it as such myself.

  • As Putnam himself writes - we have two options of interpretation: We can either say that the meaning is in the concept (the state Reg and Opp are in), and therefore that concept doesn't determine the extension (they both have same state but they refer to two different things). Either we can say that concept (meaning) does determine extension, but then we must admit that the two meanings are different because the extensions are obviously different. Putnam takes the second option as true, while in the case of indexicals he takes the first one as true. Why is it?
    – Amit Hagin
    Jul 18, 2015 at 8:12
  • @AmitHagin I'd argue that both options are true. But we are getting into uncharted territory for me, as I have not read from the source you bring up. In fact I have yet to read anything by Putnam.
    – hellyale
    Jul 18, 2015 at 8:26
  • @Amit Hagin to be honest I hope you get a better answer than what I have provided. I personally would love to see someone successfully use this arguement to prove either way for functionalism. T or F it would not be an easy feat.
    – hellyale
    Jul 19, 2015 at 2:12

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