How did Hilary Putnam’s semantic externalism explain the meaning of words?

Hilary Putnam’s semantic externalism posits that the meaning of words is not contained within the mind—famously summarized by his assertion that "meanings just ain’t in the head!" Instead, he argued that meaning is anchored in external reality.12

Under this view, meaning is primarily determined by reference (or extension)—the actual entity in the world to which a term refers. Putnam rejected the idea that meanings are merely mental images, beliefs, or definitions. His theory relies on two core pillars:1

• Causal and Social Connections: The link between a word and its referent is established through causal chains of usage and social practices (such as pointing or weighing) rather than internal mental constructs. This includes the "division of linguistic labor," where laypeople can use terms correctly by relying on the expertise of others in their community.1
• The Twin Earth Thought Experiment: Putnam demonstrated that two individuals with identical mental states and beliefs can mean different things by the same word if their environments differ. For example, "water" on Earth refers to ${\text{H}}_2\text{O}$, while on "Twin Earth," the same word refers to a different substance ($\text{XYZ}$), despite the speakers having identical mental experiences of the liquid.1

Consequently, because meaning is tied to the external world, it is context-dependent and varies with the speaker's environment and social interactions.13