The thesis of multiple realization provides a reason to prefer functionalism to the identity theory. But, depending on how we understand the notion of 'function', it may also cause troubles for functionalism. If function is understood to mean no more than merely an abstract relation between inputs, other states, and outputs, functionalism becomes so promiscuous as to allow mentality to the organization of Chinese population. On the other hand, if we impose too much causal constraint on the notion of function, functionalism becomes another anthropocentric doctrine as like the identity theory. This paper tries to seek a 'correct' form of functionalism which steers a course between an anthropocentric chauvinism and an unconstrained liberalism. It argues that a teleological functionalism founded on the notion of 'proper function' provides the most reasonable answer to the scope of multiple realization.