 Considerations about whether certain sorts of beliefs are to be externally individuated raise the related question about how best to characterize the stimulations and behaviors that serve as inputs and outputs to a system. Should they be construed as events involving objects in a system's environment (such as fire trucks, water and lemons), or rather as events in that system's sensory and motor systems? Theories of the first type are often called “long-arm” functional theories (Block 1990), since they characterize inputs and outputs — and consequently the states they are produced by and produce — by reaching out into the world. Adopting a “long-arm” theory would prevent our Twin Earth counterparts from sharing our beliefs and desires, and may thus honor intuitions that support an externalist individuation of intentional states (though further questions may remain about what Quine has called the “inscrutability of reference”; see Putnam 1988).