In the Head and the World
It is tempting to think of externalism as a view of where mental states are. The term “externalism” suggests they are located outside the head, but not all externalists think so. Not all content externalists are ready to give up on the intuition that we are in possession of our mental states. Some say that mental or psychological states are internal although representational contents are differentiated by what is external.
In Putnam’s example, what makes the content of my beliefs about water different from those of my twin are environmental relations. My internal mental state is type identical to that of my Twin Earth twin, but the world makes the semantic contents different or—as some externalists say—the world differentiates what we mean and so, in this sense, meanings are external.
The externalists hold that the meaning of water depends on an environmentally situated history of referring to water. For me to be able to mean anything by the word “water,” I need grounding in an environment with water. According to the representational account of content externalism we have been examining, our representations are not fully autonomous—they only find traction within the world as mental contents are differentiated by it.
Content externalism is often seen as having refuted Cartesianism. The mind must be understood as being world situated. We cannot make sense of meaning without the world. But content externalism does not say much about the rest of our mental lives. In particular, it does not say much about thinking—the activity that Descartes thought of as our essence. Let us see how another group of externalists—vehicle externalists—attempt to show that we are not detached thinking things, as Descartes thought.