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The China-brain objection

If organization suffices, then a crowd passing messages thinks — and one no longer sees what one has said.

Objects to The substrate does not matter

Block · "Troubles with Functionalism" · 1978

1. The argument holds that any realization of the right organization suffices, whatever the substrate: that is the decisive step, and it comes with no restriction.
2. Let us push it through: suppose the entire population of a country, equipped with telephones and instructions, reproduces exactly the causal relations of your neurons, one person per neuron. The organization, that network of causal roles, is the same, speed apart.
3. One would then have to say that a subject appears above that crowd, with its pains and memories, of which no participant has the faintest idea. The conclusion is not merely strange: nothing in the argument says why it would be true.
4. Either one accepts it, and "thinking" no longer means what we meant; or one refuses it, and then something besides organization matters: speed, material, the way the parts hold together.

Therefore Multiple realizability proves that many substrates will do, not that any will: the argument takes that step without justifying it.