 Another famous anti-reductionist thought-experiment concerning qualia appeals to the possibility of zombies. A philosophical zombie is a molecule by molecule duplicate of a sentient creature, a normal human-being, for example, but who differs from that creature in lacking any phenomenal consciousness. For me, as I lie on the beach, happily drinking some wine and watching the waves, I undergo a variety of visual, olfactory, and gustatory experiences. But my zombie twin experiences nothing at all. He has no phenomenal consciousness. Since my twin is an exact physical duplicate of me, his inner psychological states will be functionally isomorphic with my own (assuming he is located in an identical environment). Whatever physical stimulus is applied, he will process the stimulus in the same way as I do, and produce exactly the same behavioral responses. Indeed, on the assumption that non-phenomenal psychological states are functional states (that is, states definable in terms of their role or function in mediating between stimuli and behavior), my zombie twin has just the same beliefs, thoughts, and desires as I do. He differs from me only with respect to experience. For him, there is nothing it is like to stare at the waves or to sip wine.