Questions: Content Externalism and Mental Individuation

Question 1

On Twin Earth, XYZ is a liquid that looks, tastes, and behaves exactly like water but has a different molecular structure. In 1750, Oscar on Earth and his molecule-for-molecule identical Twin-Oscar both think 'water quenches thirst.' What do their thoughts refer to, according to content externalism?

• A. Both thoughts refer to the same thing — water — because their internal states are identical
• B. Oscar's thought refers to H₂O; Twin-Oscar's refers to XYZ — same internal state, different content
• C. Neither thought has definite reference in 1750, since chemistry could not yet distinguish them
• D. Both thoughts refer to the concept of water, not to any particular physical substance

Answer: (B)

This is the core of Putnam's Twin Earth argument. Because Oscar's thought is causally connected to H₂O and Twin-Oscar's to XYZ, their thoughts have different contents despite being in identical internal states. Content externalism uses this to show that content cannot be determined by what is inside the head — the external environment partly fixes what a thought is about. Option A is the internalist intuition that externalism directly refutes.

Question 2

A person has always used the word 'elm' but, unknown to them, they have consistently been pointing at beech trees. According to content externalism, what is their 'elm' thought actually about?

• A. Elms, because that is the word they chose to use
• B. Beeches, because that is what their thought was actually caused by and connected to in their environment
• C. Nothing — systematically mistaken reference means the thought lacks content
• D. It depends on what they consciously intend, which introspection can settle

Answer: (B)

Content externalism holds that what fixes the reference of a thought is partly the external causal connection to things in the world, not just internal intention or word choice. This extends Burge's social externalism: even a single person's idiolect is anchored by the world they are embedded in. Option D is what internalists would expect — that introspection reveals content — but externalists deny this, since introspection cannot reveal which substance is actually out there.

Question 3

According to content externalism, you can fully know what your own thoughts are about through careful introspection alone.

• T. True
• F. False

Answer: False

Content externalism implies that mental content depends on external facts — what substance 'water' actually refers to, what kind of tree 'elm' actually picks out. Introspection gives you access only to your internal states, not to facts about the external world that partly constitute your thought's content. You might introspect perfectly and still not know that you are on Twin Earth thinking about XYZ rather than H₂O. This is one of the most counterintuitive implications of the view.

Question 4

Content externalism implies that two individuals in identical brain states could hold different beliefs about the world.

• T. True
• F. False

Answer: True

This is the direct conclusion of the Twin Earth argument. Oscar and Twin-Oscar are molecule-for-molecule identical, yet Oscar believes something about H₂O while Twin-Oscar believes something about XYZ. Since beliefs are individuated by their content, and content differs, their beliefs differ — despite identical internal states. This challenges the assumption that mental states supervene on brain states alone.

Question 5

What does the Twin Earth thought experiment show about where mental content comes from?

Model answer: It shows that mental content cannot be determined solely by internal brain states. Oscar and Twin-Oscar have identical neural states, yet their 'water' thoughts refer to different substances (H₂O vs. XYZ). Whatever fixes content must therefore lie outside the head — in the actual substances their thoughts are causally connected to in their respective environments. Content is individuated externally, not internally.

The force of the argument depends on the stipulation that all internal states are identical. If the twins are truly indistinguishable from the inside yet their thoughts differ in content, then content cannot be an internal matter. This is what it means to say minds are not 'in the head' in the sense relevant to content — the world contributes to making a thought the specific thought it is.