Could a mind made of anything — silicon, string or neurons — still be a mind?

Functionalism says it could. A mental state isn't defined by what it's made of. It's defined by what it does: its causal role. Take pain. It's caused by injury. It leads to other states, like distress. And it causes behavior, like wincing. Anything that plays that role, in neurons or in silicon, would be in pain.

The philosopher Hilary Putnam proposed the first version in the 1960s. He was inspired by Alan Turing's abstract machines. Functionalists compare a mental state to a valve. A valve can be plastic or metal. What matters is that it controls the flow. On this view, a silicon machine could have the same sort of mental life as a human. It just needs the right functional organization.

This turns an old objection into a strength. Identity theory said pain is one specific kind of brain state. But pain shows up in very differently built nervous systems. For functionalism, that's no surprise. One role can be filled by many different materials.

Critics push back. The "China brain" thought experiment wires up the whole nation of China, each person acting as one neuron. Would that country be a mind? Ned Block finds that implausible, a sign something is wrong with the theory. Even Putnam began doubting his own version by the mid-1970s. Still, in a 2020 survey of philosophers, functionalism was the most popular theory of mind: 33%, against 22% for dualism.