 The simplest way to account for madmen would be to simply identify pain with a neural state. So Lewis’s identity theory is well-placed to deal with them. But there is a complication. Not every creature in the universe who is in pain has the same neural states as us. It is at least possible that there are creatures in which some silicon state S plays the pain role. That is, the creatures are averse to S, they take S to be an indicator of bodily damage, and so on. Those creatures are in pain whenever they are in state S. Call any such creature a Martian. A simple identification of pain with neural state N will stipulate that there couldn’t be any Martians. That would be a bad stipulation to make.