Content externalism
Explanation
Hilary Putnam, in his article The Meaning of 'Meaning' (1975), proposed an influential thought experiment: Twin Earth. Imagine a planet exactly like ours except for one detail: what they call water there is not H2O but a different substance XYZ, visually identical. My twin on Twin Earth and I have neurophysiologically identical mental states, but when he says water he refers to XYZ and when I say water I refer to H2O.
The conclusion Putnam draws is provocative: meanings are not in the head. The content of my thoughts is not entirely determined by what is going on inside my brain; it depends also on the physical and social environment in which the brain is situated. Two identical brains can have different thoughts if they are in different worlds.
Tyler Burge extended this externalism to conceptual content in general. His thought experiments on arthritis showed that if my community's linguistic conventions change, the content of my thoughts about arthritis changes too, even without changes in my brain. Meaning depends on social practices, not only on individual neurobiology.
Externalism poses serious challenges for internalist theories of mind. If mental content is externalist, then neuroscience alone cannot determine what someone is thinking: it also needs to know the subject's physical and historico-social environment. This has implications for causal explanation: what causes behaviour, brain states or externalist contents?
Several positions have responded to externalism. Internalism insists that what is causally relevant are narrow contents (those depending only on the brain). Two-factor versions distinguish broad and narrow content, giving each a distinct theoretical role. And global versions hold that all content is externalist, including the apparently internal.
For consciousness, externalism suggests that what we experience does not depend only on brain processes but also on how we are situated in the world. This idea connects with extended mind, embodied cognition, enactivism and other 4E proposals. In all of them, the conscious self is not reducible to isolated neurons but extends across a wider network of relations with the physical and social environment.
Strengths
- An elegant and clarifying argument.
- Coherent with scientific practices of content individuation.
- Inspiration for theories of extended mind.
- Reformulates Cartesian internalism.
Main critiques
- Some hold that it conflates meaning with reference.
- Refined internalism (narrow content) remains possible.
- Difficult articulation with subjective phenomenology.
- Questions epistemic privilege without replacing it.