Zombies are hypothetical creatures which are functionally identical to us, but they lack qualia altogether. If they are possible, functionalism can’t be right. If such possibilities are conceivable, perhaps it means that functionalism is at least conceivably wrong.

There are a few senses in which zombies can be functionally identical to us. Suppose we merely mean they can refer to and act on the same objects in the world like we do. Then sure some robot-like creatures can interact with objects in the world without being conscious.

But if we mean that they are functionally fully identical to us, as in the whole mental algorithm is consistent with what we have, then we should recognize that they can’t be coherently conceived to be nonconscious. Such ‘zombies’ will know what it is like to have certain experiences. They can tell you scarlet is a bit like crimson, not much like pink or purple, etc, from a subjective point of view. This means, if you ask them if there is something it is like to see colors, they will truthfully say yes, for the same reasons we do. On the other hand, if you ask them what it is like to experience some subthreshold firing of neurons in the visual cortex, it should draw a blank. And this would not be merely because they don’t know enough about neuroscience. Even if you actually stimulate their visual cortices that way, they still wouldn’t know what you were talking about. In this sense, they are just like us.

Of course, the anti-functionalist can say that they only behave or talk as if they consciously see. But how else do you know if anyone is conscious, besides their expressing that they think so and your lack of reason to doubt that they are lying or deluded?

Let’s say we have some Martians, who truthfully agree with us that there is something it is like to see red and other colors. And yet, when asked what it is like to smell, it draws a blank. If odors could nevertheless influence their behavior, we probably would think that they have olfactory processing. In that case, what else apart from consciousness can account for the difference between their vision and olfaction? According to them, in one modality, there is something it is like, and in the other, there isn’t. If they aren’t lying or crazy, what else is the difference?

This is to say, if a creature is capable of thinking meaningfully whether there is something it is like to have a certain experience, then whether the creature is inclined to truthfully think so is the truth of the matter. As such, zombies in a fully functional sense are simply not coherently conceivable. Either they truthfully think there is something it is like to have some experiences, in which case they aren’t zombies; or they do not think so, in which case they are not functionally like us at all.

[this literature is vast and mine will never be the last words, of coz. hence this is a blogpost not a paper. my goal is just to hopefully convince some of my scientist colleagues that some functionalist defense is possible, and it needn’t be overly complicated.]