The same mental state can be built from completely different physical stuff

Hilary Putnam argued in 1967 that pain or belief isn't tied to one physical structure, since an octopus, a human, and, hypothetically, a silicon-based alien could all feel pain despite utterly different nervous systems. If a mental state is 'multiply realizable' this way, it can't be identical to any one type of brain state, as mind-brain identity theory claimed. The argument helped launch functionalism, the idea that mental states are defined by what they do, not what they're made of.

— Hilary Putnam, Psychological Predicates — 1967; later retitled 'The Nature of Mental States'