No, not those zombies! They aren’t merely possible, they are actual, as you can see. →

Rather, our topic today is philosophical zombies, beings that are physically identical to us but without conscious experience. Thus, a zombie version of yourself, for instance, would be atom-for-atom identical to you. It would share all of your behavioral dispositions: it would walk like you, talk like you, have the same tendencies to be angry, happy, or sad as you, report any information that you are able to report, and perform any tasks that you are able to perform. It would also remember everything that you can remember, know everything that you know, and it would have all the same politics and cultural attitudes and biases as you. At least, it would do all these things as near as we could tell. It would be behaviorally and neurophysiologically identical to you. There would be no way for another person to tell that your zombie twin was not you merely by comparing you with it, no matter what tests he might arrange. Nevertheless, your zombie twin would not be the same as you, because it would not have consciousness. That is, it would not have subjective experience. In the phrase widely adopted from Thomas Nagel’s well-known essay, “What Is It Like to Be a Bat?”, there would be nothing it is like to be your zombie twin.

Philosophical zombies are a way to make vivid an old philosophical argument, going back at least to Descartes, known as the Conceivability Argument. In the present version, the idea is that it is conceivable that the world could be just as it is physically down to the last elementary particle, but without conscious experience. That is, we could have had the Big Bang and the evolution of the universe just as it is, including the evolution of life on earth and the human species, and physically everything would be just as it is today, including all of us having discussions just like this one, although none of us nor any other beings have conscious experience. By conceivable, I mean there is no contradiction in this scenario and no reason that science can discover, whether physical, psychological, or otherwise, why it could not have happened. If this scenario is conceivable, then it seems we must conclude that consciousness is epiphenomenal: it is nonphysical, it cannot be explained by the physical, and its presence or absence makes no difference to the causal, functional, or physical order of nature.