By now, even the kid down the street must be familiar with the functionalist's response to type-identity physicalism. Mental kinds like pain, love, the belief that Madison sits on an isthmus, etc., are not identical to physical kinds because it's conceptually (if not empirically) possible that entities physically distinct in kind from human beings experience pain, love, beliefs that Madison sits on an isthmus, etc. Type-identity physicalism, in short, is baselessly chauvinistic in its rejection of the possibility of nonhuman minds.

Perhaps less familiar, but still widely acknowledged, is the following Trouble with Functionalism. Functional characterizations of mental kinds are hopelessly unconstrained. If mental kinds are defined simply in terms of relations between inputs, other states, and outputs, then such obviously mindless things as the nation of China and the Bolivian economy (Block, 1978; 1980) might end up having minds.

It's worth noting that the points both in favour of and against functionalism depend substantially on unfettered intuition. Why believe that something without a brain like ours can have a mind? To date, no artificial intelligences have come close to matching a human being's mental abilities and no extraterrestrial intelligences have been discovered. Robots like Commander Data and alien geniuses like Spock remain nothing more than an intuitively plausible challenge to physicalism. Similarly, it's nothing but intuition that makes us believe that the nation of China or the Bolivian economy cannot have minds.