Semantic Externalism

Author: Rachel Bourbaki
Category: Philosophy of Mind and Language
Word Count: 1000

1. Internalism and Externalism

Examples of mental phenomena are things like pain, joy, and perceptual states. Internalism about mental phenomena is the view that all mental phenomena are spatially located inside the brain or skin of the creature that possesses them. Externalism about mental phenomena is the view that not all mental phenomena are exclusively located inside the skull or skin of the creature that has them (Rowlands 2003, 2).

Language, one component of the bedrock of human cognition, includes terms that have meaning. But where do these meanings come from? Semantic externalism, a species of externalism about mental phenomena, is the view that the meanings of terms are not fully determined by factors internal to the speaker, but are instead bound up with the speaker’s environment (Kallestrup 2012, i). Meanings, according to semantic externalism, are not to be found merely in the head.

2. Meaning and the Intension and Extension of Terms

The intension of a term is the internal concept or idea that goes along with it—similar in many ways to the definition of a term. The intension of the term ‘book,’ for instance, is the idea of a bound copy, including a front and back cover, with many pages in between. The extension of a term is simply the set of things that that term applies to or is true of. The extension of the term ‘book’ will include all actual books in the world, be they dictionaries, copies of Harry Potter, or the Summa Theologiæ.

Hilary Putnam, in his seminal paper, “The Meaning of ‘Meaning’” (1975), challenges the assertion that knowing the meaning of a term is just a matter of being in a certain psychological state (i.e., he challenges the thesis of semantic internalism). Namely, Putnam thinks that two persons can be in the same psychological state while the terms they use have different meanings. This is because two persons can be in the same psychological state while the extensions of the term they are using differ.

3. Semantic Internalism and Externalism

The traditional view of meaning—the internalist view—rests on the assumption that knowing the meaning of a term is just a matter of being in a certain psychological state (Wikforss 2008, 160). It follows from this assumption, Putnam suggests, that the psychological state of the speaker determines the meaning of the term being used by a speaker (Wikforss 2008, 160).

Semantic externalism tells us that this isn’t true. Instead, the external environment “plays a role in the determination of meaning” (Wikforss 2008, 159). In virtue of what does a term like ‘water’ or ‘tiger’ or ‘aluminum’ have the meaning that it does? According to the semantic externalist, these meanings are determined at least in part by features of the external world.

Let’s start by contemplating the meaning of the word ‘water.’ Putnam famously uses the idea of Twin Earth in a thought experiment in order to show that the meaning of this term is partially determined by external facts in the world. First, imagine a planet, Twin Earth, which is nearly identical to regular Earth. In fact, people on Earth have exact (physical, biological, and psychological) copies of themselves on Twin Earth. However, there is one peculiarity of Twin Earth as it compares to regular Earth. On Twin Earth, the liquid called ‘water’ is not H2O but is instead XYZ, which behaves in exactly the same ways as H2O does on regular Earth—it flows in rivers, falls from the sky in the form of rain, is drinkable for Twin-Earthlings, etc. (See Putnam 1975). But, although XYZ is superficially like water, and is called ‘water’ by twin-Earthlings, it is not water because it has a different chemical composition (Kallestrup 2012, 59).

Now, say there are two speakers named ‘Oscar’ and ‘Twin-Oscar’ on Earth and Twin Earth, respectively. Oscar and Twin-Oscar are exact copies of one another. One thinks ‘water’ while observing H2O, and the other thinks ‘water’ when observing XYZ. The term ‘water’ used by Oscar on Earth differs in meaning from the term used by his twin on Twin Earth, despite the fact that the two, Oscar and Twin-Oscar, are in identical psychological states. The twins share psychological states in virtue of sharing beliefs about what they call ‘water’ (Kallestrup 2012, 59). Oscar and Twin-Oscar have associated all the same descriptions with their respective term ‘water’ (i.e., that it is colorless, transparent, tasteless, thirst-quenching, etc.). But their respective terms have different extensions because Oscar and Twin-Oscar are situated in environments that differ in the essential respect that on Earth, the liquid called ‘water’ has the chemical composition H2O, whereas on Twin Earth, it has the entirely different chemical composition XYZ (Wikforss 2008, 160). When Oscar uses the term ‘water,’ he refers to H2O, and when Twin-Oscar uses the term ‘water,’ he refers to XYZ. Since the terms refer to different things, Oscar and Twin-Oscar mean different things when they use the term. Because Oscar and Twin-Oscar are exactly internally alike, what they mean is determined “behind their backs” by hidden features of their physical environment (Kallestrup 2012, 90). The meanings are different because the stuff they are referring to is different; thus, according to Putnam “meanings just ain’t in the head” (Putnam 1975, 144).

The moral of this thought experiment is that we ought to give up thinking that the psychological state of a speaker determines the meaning of the term she uses. Defenders of internalism might reply that Oscar and Twin-Oscar only deploy the broad concept of ‘the watery stuff’ when they think or use the term ‘water.’ This concept does not include the microstructure of the watery stuff in question. And both H2O and XYZ will fall under this description. Like the word ‘vitamin,’ which picks out distinct organic compounds, ‘water’ also picks out distinct substances as long as they are sufficiently watery (Kallestrup 2012, 65). If this is true, then the two speakers do mean the same thing when they use the term ‘water.’

If we accept this internalist rejoinder, we also must accept that XYZ really is water, which flies in the face of scientific practice—‘water’ is H2O, say chemists. There may be some ways in which the internalist might improve on the above defense, but the threat of semantic externalism continues to loom large on the horizon.


Kallestrup, Jesper. Semantic Externalism. New York: Routledge (2012).

Putnam, Hilary. “The Meaning of ‘Meaning’”. Minnesota Studies in the Philosophy of Science, Vol. 7 (1975). pp. 131-193.

Rowlands, Mark. Externalism: Putting Mind and World Back Together Again. Ithaca: McGill-Queen’s University Press (2003).

Wikforss, Asa. “Semantic Externalism and Psychological Externalism”. Philosophy Compass, Vol. 3, No.1 (2008). pp. 158-181. 



About the Author

Rachel has a PhD in philosophy. She is interested in philosophy of mind, philosophy of cognitive science, action theory, and free will and moral responsibility. In her free time, she enjoys hiking, cycling, and participating in other outdoor activities.

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