Oscar on Earth and Twin Oscar on Twin Earth are atom-for-atom identical. Oscar's 'water' refers to H2O; Twin Oscar's 'water' refers to XYZ. What does this show about mental content?
AMental content is entirely determined by the speaker's internal psychological state
BThe word 'water' is meaningless on Twin Earth because XYZ isn't genuine water
CTwo people with identical internal states can have thoughts with different semantic content
DLanguage must be grounded in scientific knowledge to have determinate reference
The key intuition is that Oscar and Twin Oscar are internally identical — same neurons, same functional states, same mental imagery — yet their 'water'-thoughts have different truth conditions and pick out different substances. This shows that semantic content is not fixed by internal states alone. It depends partly on the environment and the causal history connecting the term to its referent. Option A is exactly what Twin Earth is designed to refute.
Question 2 Multiple Choice
Putnam sets the Twin Earth thought experiment in 1750, before modern chemistry. Why does this timing matter?
ABecause pre-scientific language lacks determinate reference and the argument only applies there
BBecause Oscar and Twin Oscar cannot know their 'water' differs chemically — their environment, not their beliefs or knowledge, determines what their terms refer to
CBecause the French Academy had not yet standardized the meaning of 'water' across languages
DBecause philosophical thought experiments are only valid when set in historical periods
Setting the scenario in 1750 is crucial: neither Oscar nor Twin Oscar has any chemical knowledge that could distinguish H2O from XYZ. Their conscious beliefs, descriptions, and mental images associated with 'water' are therefore identical. Yet their terms still refer to different substances. This isolates the environmental factor: what fixes reference is not what the speaker knows or believes (which is the same for both), but the actual nature of the stuff in their environment and the causal chain to it.
Question 3 True / False
The Twin Earth thought experiment is a philosophical argument whose force depends on a conceivable scenario, not on whether XYZ could actually exist.
TTrue
FFalse
Answer: True
Putnam is making a point about the conceptual relationship between internal mental states and semantic content, not a claim about physics. The scenario only needs to be imaginable enough to pump the intuition that Oscar and Twin Oscar mean different things. Objecting that Twin Earth is 'scientifically impossible' misses the nature of the argument — philosophical thought experiments regularly use stipulated impossible cases to test conceptual claims.
Question 4 True / False
According to Putnam's Twin Earth argument, the difference in meaning between Oscar's and Twin Oscar's use of 'water' is explained by a difference in their internal psychological states.
TTrue
FFalse
Answer: False
This is precisely what Twin Earth disproves. Oscar and Twin Oscar have identical internal psychological states — that is a stipulated condition of the thought experiment. Yet their terms have different extensions. Therefore, the difference in meaning cannot be explained internally. It must be explained by facts external to the speakers: what substance is actually in their respective environments and causally connected to their use of the term.
Question 5 Short Answer
What does Putnam's slogan 'it ain't in the head' mean, and what does Twin Earth show about internalist theories of meaning?
Think about your answer, then reveal below.
Model answer: 'It ain't in the head' means that what our words refer to — their extension — is not determined solely by whatever is going on in the speaker's mind (mental images, descriptions, functional roles). Twin Earth shows that two speakers can have identical internal states yet use the same word to refer to different things. Any theory that individuates semantic content purely by internal states will wrongly predict that Oscar and Twin Oscar mean the same thing by 'water.' The correct account must include the environment and the causal-historical chain linking the word to its referent.
This is the core externalist insight: reference is partly a matter of how you are causally connected to the world, not just what you think or believe. This has major consequences for both philosophy of language and philosophy of mind — it means that two functionally identical mental states can differ in their content, which challenges purely internalist accounts of thought.