Putnam, Hilary ‘Meaning and Reference,’ The Journal of Philosophy 70: 19, (1973): 699-711.
Putnam seeks to undermine two doctrines of standard semantic theory (“theory of meaning,” in a broad sense) via the use of a thought experiment. The doctrines are: one, that intension (‘meaning’, more or less) determines extension (‘reference’, more or less) and in fact is always sufficient for doing so (such that two terms with the same intension must have the same extension); and, two, that intensions are concepts and thus psychological entities (such that two persons in the same psychological state must be grasping the same extension with regards to a term they both use). After presenting his thought experiment, Putnam presents an alternative thesis to explain how groups of speakers utilize intensions if not as psychological entities that fix extension, and argues that his view necessitates that natural kind terms (e.g., ‘water’ or ‘gold’) are rigid designators.
Putnam asks us to consider a world called ‘Twin Earth’ which is exactly similar to Earth – including in the languages spoken, physical properties exhibited by all things, and so forth – except that on Twin Earth, the liquid called ‘water’ isn’t H20, but rather is a molecule with a complicated chemical formula, abbreviated ‘XYZ’. XYZ functions just as H20 does on Earth, occupying the same space and exhibiting all the same physical properties. In other
words, the average resident of either planet would not be able to distinguish H20 from XYZ.
Putnam then modifies the thought experiment such that it becomes a counterexample to the notion that the doctrines can be jointly maintained: Putnam asks us to consider speakers on Earth and Twin Earth that existed before either planet’s scientific communities determined the precise molecular formula for water (on Earth) and ‘water’ (on Twin Earth). Such speakers will stand in the exact same psychological relation to the liquid they call ‘water’ (since the sole dissimilarity between Earth and Twin Earth – the fact that water is H20 and ‘water’ XYZ – is unknown to the speakers), despite the fact that in either instance a different liquid is under consideration. Thus, two persons in the same psychological state nonetheless are grasping a different extension. Yet if both doctrines were true – if intension were always sufficient to determine extension and if intensions were psychological entities – then sameness of psychological state would entail sameness of extension for the term being used. Putnam uses this result to indicate that it is false that intensions are psychological entities.
Putnam presents a further altered version of the thought experiment in order to reinforce the same conclusion about intensions not being psychological: supposing that pots and pans made of aluminum and molybdenum are indistinguishable, that pots and pans are made of aluminum on Earth and molybdenum on Twin Earth, and that on Twin Earth the words ‘aluminum’ and ‘molybdenum’ are switched (such that Twin Earthians refer to what we call aluminum with the word ‘molybdenum’), then speakers from Earth who travel to Twin Earth will be in the same psychological state as the locals with regard to pots and pans, yet will be referring to different things. Thus, sameness of psychological state does not entail sameness of extension; further, intensions are not psychological states: in this instance an Earth speaker and Twin Earth speaker are in the same psychological state yet are using a word to indicate a different meaning.
Putnam presents an alternative vision for how communities of speakers utilize intensions: the use of a word is a communal activity, with a “division of labor” (704) distributing the burden of proper use across a community. In other words, rather than the use of a word depending upon a solipsistic grasping of an intension (which then makes an extension clear) on the part of every speaker of a word, some in the community may simply provide ostensive definitions of words, while others (the scientifically oriented ones) may do the actual work of explicating the extension of terms. The proper determination/utilization of intensions and extensions arises from this communal work, not from the individual psychology of any given speaker.
Putnam then undermines the doctrine that intension necessarily determines extension by launching a discussion of natural kind terms – of which ‘water’ is an example. Putnam thinks that such terms are defined ostensively, i.e., by pointing to a thing in the world as an exemplar of the meaning of the term. To Putnam, to the extent that such terms are defined ostensively, their extension actually determines their intension, in the sense that a paraphrase of the meaning of the term will be of the general form ‘this thing right here,’ perhaps with an accompanying demonstration (e.g., a pointed finger). And the precise meaning of such a paraphrase will be determined by whatever the demonstratum (thing being demonstrated, pointed at) actually is. And this makes it possible for one to not know what is truly ‘meant’ by such a term until a scientific investigation reveals the thing ostended.
Besides undermining the notion that intension always determines extension, Putnam thinks that natural kind terms having as their intension their extension makes it such that these terms are ‘rigid designators’, or terms that refer to the same thing in all possible worlds. This is because a natural kind term is established (“baptized” one might say) via ostension, which relates to the actual world. Thus, such a baptismal rite will go something like, ‘Natural kind term n means this thing in the actual world’, meaning that the way the world is for Putnam as much a contributor in determining reference as is any psychological state on the part of speakers, contrary to standard semantic theory.