Zombies Redacted

I looked at my old post Zom­bies! Zom­bies? and it seemed to have some ex­tra­ne­ous con­tent. This is a redacted and slightly rewrit­ten ver­sion.


Your “zom­bie”, in the philo­soph­i­cal us­age of the term, is pu­ta­tively a be­ing that is ex­actly like you in ev­ery re­spect—iden­ti­cal be­hav­ior, iden­ti­cal speech, iden­ti­cal brain; ev­ery atom and quark in ex­actly the same po­si­tion, mov­ing ac­cord­ing to the same causal laws of mo­tion—ex­cept that your zom­bie is not con­scious.

It is fur­ther­more claimed that if zom­bies are “con­ceiv­able” (a term over which bat­tles are still be­ing fought), then, purely from our knowl­edge of this “con­ceiv­abil­ity”, we can de­duce a pri­ori that con­scious­ness is ex­tra-phys­i­cal, in a sense to be de­scribed be­low.

See, for ex­am­ple, the SEP en­try on Zom­bies. The “con­ceiv­abil­ity” of zom­bies is ac­cepted by a sub­stan­tial frac­tion, pos­si­bly a ma­jor­ity, of aca­demic philoso­phers of con­scious­ness.


I once read some­where, “You are not the one who speaks your thoughts—you are the one who hears your thoughts”.

If you con­ceive of “con­scious­ness” as a quiet, pas­sive listen­ing, then the no­tion of a zom­bie ini­tially seems easy to imag­ine. It’s some­one who lacks the the in­ner hearer.

Sketch­ing out that in­tu­ition in a lit­tle more de­tail:

When you open a re­friger­a­tor and find that the or­ange juice is gone, you think “Darn, I’m out of or­ange juice.” The sound of these words is prob­a­bly rep­re­sented in your au­di­tory cor­tex, as though you’d heard some­one else say it.

Why do I think the sound of your in­ner thoughts is rep­re­sented in the au­di­tory cor­tex, as if it were a sound you’d heard? Be­cause, for ex­am­ple, na­tive Chi­nese speak­ers can re­mem­ber longer digit se­quences than English-speak­ers. Chi­nese digits are all sin­gle syl­la­bles, and so Chi­nese speak­ers can re­mem­ber around ten digits, ver­sus the fa­mous “seven plus or minus two” for English speak­ers. There ap­pears to be a loop of re­peat­ing sounds back to your­self, a size limit on work­ing mem­ory in the au­di­tory cor­tex, which is gen­uinely phoneme-based.

It’s not only con­ceiv­able in prin­ci­ple, but pos­si­bly pos­si­ble in the next cou­ple of decades, that sur­geons will lay a net­work of neu­ral taps over some­one’s au­di­tory cor­tex and read out their in­ter­nal nar­ra­tive. Re­searchers have already tapped the lat­eral genicu­late nu­cleus of a cat and re­con­structed rec­og­niz­able vi­sual in­puts.

So your zom­bie, be­ing phys­i­cally iden­ti­cal to you down to the last atom, will open the re­friger­a­tor and form au­di­tory cor­ti­cal pat­terns for the phonemes “Darn, I’m out of or­ange juice”. On this point, p-zom­bie ad­vo­cates agree.

But in the Zom­bie World, allegedly, there is no one in­side to hear; the in­ner listener is miss­ing. The in­ter­nal nar­ra­tive is spo­ken, but un­heard. You are not the one who speaks your thoughts, you are the one who hears them.

The Zom­bie Ar­gu­ment is that if the Zom­bie World is pos­si­ble—not nec­es­sar­ily phys­i­cally pos­si­ble in our uni­verse, just “pos­si­ble in the­ory”, or “con­ceiv­able”—then con­scious­ness must be ex­tra-phys­i­cal, some­thing over and above mere atoms. Why? Be­cause even if you knew the po­si­tions of all the atoms in the uni­verse, you would still have be told, as a sep­a­rate and ad­di­tional fact, that peo­ple were con­scious—that they had in­ner listen­ers—that we were not in the Zom­bie World.

The tech­ni­cal term for the be­lief that con­scious­ness is there, but has no effect on the phys­i­cal world, is epiphe­nom­e­nal­ism.

Though there are other el­e­ments to the zom­bie ar­gu­ment (I’ll deal with them be­low), I think that the in­tu­ition of the in­ner listener is what first per­suades peo­ple to zom­bie-ism. The core no­tion is sim­ple and easy to ac­cess: The lights are on but no­body’s home.

Philoso­phers are ap­peal­ing to the in­tu­ition of the quiet, pas­sive in­ner listener when they say “Of course the zom­bie world is imag­in­able; you know ex­actly what it would be like.”

But just be­cause you don’t see a con­tra­dic­tion in the Zom­bie World at first glance, it doesn’t mean that no con­tra­dic­tion is there. Just be­cause you don’t see an in­ter­nal con­tra­dic­tion yet within some set of gen­er­al­iza­tions, is no guaran­tee that you won’t see a con­tra­dic­tion in an­other 30 sec­onds. “All odd num­bers are prime. Proof: 3 is prime, 5 is prime, 7 is prime...”

So let us pon­der the Zom­bie Ar­gu­ment a lit­tle longer: Can we think of a coun­terex­am­ple to the as­ser­tion “Con­scious­ness has no third-party-de­tectable causal im­pact on the world”?

If you close your eyes and con­cen­trate on your in­ward aware­ness, you will be­gin to form thoughts, in your in­ter­nal nar­ra­tive, along the lines of “I am aware” and “My aware­ness is sep­a­rate from my thoughts” and “I am not the one who speaks my thoughts, but the one who hears them” and “My stream of con­scious­ness is not my con­scious­ness” and “It seems like there is a part of me which I can imag­ine be­ing elimi­nated with­out chang­ing my out­ward be­hav­ior.”

You can even say these sen­tences out loud. In prin­ci­ple, some­one with a su­per-fMRI could prob­a­bly read the phonemes right out of your au­di­tory cor­tex; but say­ing it out loud re­moves all doubt about whether you have en­tered the realms of phys­i­cally visi­ble con­se­quences.

This cer­tainly seems like the in­ner listener is be­ing caught in the act of listen­ing by what­ever part of you writes the in­ter­nal nar­ra­tive, a causally po­tent neu­ral pat­tern in your au­di­tory cor­tex, which can even­tu­ally move your lips and flap your tongue.

Imag­ine that a mys­te­ri­ous race of aliens visit you, and leave you a mys­te­ri­ous black box as a gift. You try pok­ing and prod­ding the black box, but (as far as you can tell) you never elicit a re­ac­tion. You can’t make the black box pro­duce gold coins or an­swer ques­tions. So you con­clude that the black box is causally in­ac­tive: “For all X, the black box doesn’t do X.” The black box is an effect, but not a cause; epiphe­nom­e­nal, with­out causal po­tency. In your mind, you test this gen­eral hy­poth­e­sis to see if the gen­er­al­iza­tion is true in some trial cases, and it seems to be true in ev­ery one—”Does the black box re­pair com­put­ers? No. Does the black box boil wa­ter? No.”

But you can see the black box; it ab­sorbs light, and weighs heavy in your hand. This, too, is part of the dance of causal­ity. If the black box were wholly out­side the causal uni­verse, you wouldn’t be able to see it; you would have no way to know it ex­isted; you could not say, “Thanks for the black box.” You didn’t think of this coun­terex­am­ple, when you for­mu­lated the gen­eral rule: “All X: Black box doesn’t do X”. But it was there all along.

(Ac­tu­ally, the aliens left you an­other black box, this one purely epiphe­nom­e­nal, and you haven’t the slight­est clue that it’s there in your liv­ing room. That was their joke.)

If some­thing has no causal effect, you can’t know about it. The ter­ri­tory must be causally en­tan­gled with the map for the map to cor­re­late with the ter­ri­tory. To ‘see’ some­thing is to be af­fected by it. If an allegedly phys­i­cal thing or prop­erty has ab­solutely no causal im­pact on the rest of our uni­verse, there’s a se­ri­ous ques­tion about whether we can even talk about it, never mind jus­tifi­ably know­ing that it’s there.

It is a stan­dard point—which zom­bie-ist philoso­phers ac­cept!—that the Zom­bie World’s philoso­phers, be­ing atom-by-atom iden­ti­cal to our own philoso­phers, write iden­ti­cal pa­pers about the philos­o­phy of con­scious­ness.

At this point, the Zom­bie World stops be­ing an in­tu­itive con­se­quence of the idea of an in­ner listener.

Philoso­phers writ­ing pa­pers about con­scious­ness would seem to be at least one effect of con­scious­ness upon the world. You can ar­gue clever rea­sons why this is not so, but you have to be clever. You are no longer play­ing straight to the in­tu­ition.

Let’s say you’d never heard of the Zom­bie World and never formed any ex­plicit gen­er­al­iza­tions about how zom­bies are sup­posed to ex­ist. The thought might spon­ta­neously oc­cur to you that, as you stand and watch a beau­tiful sun­set, your aware­ness of your aware­ness could be sub­tracted from you with­out chang­ing your out­ward smile. But then ask whether you still think “I am aware of my in­ner aware­ness”, as a neu­ral pat­tern in your au­di­tory cor­tex, and then say it out loud, af­ter the in­ner aware­ness has been sub­tracted. I would not ex­pect the gen­er­al­iza­tion “my in­ner aware­ness has no effect on phys­i­cal things” to still seem in­tu­itive past that point, if you’d never been ex­plic­itly in­doc­tri­nated with p-zom­bieism.

In­tu­itively, we’d sup­pose that if your in­ward aware­ness van­ished, your in­ter­nal nar­ra­tive would no longer say things like “There is a mys­te­ri­ous listener within me,” be­cause the mys­te­ri­ous listener would be gone and you would not be think­ing about it. It is usu­ally im­me­di­ately af­ter you fo­cus your aware­ness on your aware­ness, that your in­ter­nal nar­ra­tive says “I am aware of my aware­ness”; which sug­gests that if the first event never hap­pened again, nei­ther would the sec­ond.

Once you see the col­li­sion be­tween the gen­eral rule that con­scious­ness has no effect, to the spe­cific im­pli­ca­tion that con­scious­ness has no effect on how you think about con­scious­ness (in any way that af­fects your in­ter­nal nar­ra­tive that you could choose to say out loud), zom­bie-ism stops be­ing in­tu­itive. It starts re­quiring you to pos­tu­late strange things.

One strange thing you might pos­tu­late is that there’s a Zom­bie Master, a god within the Zom­bie World who sur­rep­ti­tiously takes con­trol of zom­bie philoso­phers and makes them talk and write about con­scious­ness.

Hu­man be­ings of­ten don’t sound all that co­her­ent when talk­ing about con­scious­ness. It might not be that hard to fake. Maybe you could take, as a cor­pus, one thou­sand hu­man am­a­teurs try­ing to dis­cuss con­scious­ness; feed them into a suffi­ciently pow­er­ful but non-re­flec­tive ma­chine learn­ing al­gorithm; and get back dis­course about “con­scious­ness” that sounded as sen­si­ble as most hu­mans, which is to say, not very.

But this speech about “con­scious­ness” would not be pro­duced within the AI. It would be an imi­ta­tion of some­one else talk­ing. You might as well ob­serve that you can make a video record­ing of David Chalmers (the most formidable ad­vo­cate of zom­bieism) and play back the record­ing. The cause that shaped the pat­tern of the words in the video record­ing was Chalmers’s con­scious­ness mov­ing his lips; that shap­ing cause is merely be­ing trans­mit­ted through a medium, like sounds pass­ing through air.

A sep­a­rate, ex­tra Zom­bie Master is not what the philo­soph­i­cal Zom­bie World pos­tu­lates. It’s as­sert­ing that the atoms in the brain are quark-by-quark iden­ti­cal, mov­ing un­der ex­actly the same phys­i­cal laws we know; there’s no sep­a­rate, ad­di­tional Zom­bie Master AI Chat­bot mak­ing the lips move in ways that were copied off the real David Chalmers. The zom­bie you’s lips are talk­ing about con­scious­ness for the same causal rea­son your lips talk about con­scious­ness.

As David Chalmers writes:

Think of my zom­bie twin in the uni­verse next door. He talks about con­scious ex­pe­rience all the time—in fact, he seems ob­sessed by it. He spends ridicu­lous amounts of time hunched over a com­puter, writ­ing chap­ter af­ter chap­ter on the mys­ter­ies of con­scious­ness. He of­ten com­ments on the plea­sure he gets from cer­tain sen­sory qualia, pro­fess­ing a par­tic­u­lar love for deep greens and pur­ples. He fre­quently gets into ar­gu­ments with zom­bie ma­te­ri­al­ists, ar­gu­ing that their po­si­tion can­not do jus­tice to the re­al­ities of con­scious ex­pe­rience.

And yet he has no con­scious ex­pe­rience at all! In his uni­verse, the ma­te­ri­al­ists are right and he is wrong. Most of his claims about con­scious ex­pe­rience are ut­terly false. But there is cer­tainly a phys­i­cal or func­tional ex­pla­na­tion of why he makes the claims he makes. After all, his uni­verse is fully law-gov­erned, and no events therein are mirac­u­lous, so there must be some ex­pla­na­tion of his claims.

...Any ex­pla­na­tion of my twin’s be­hav­ior will equally count as an ex­pla­na­tion of my be­hav­ior, as the pro­cesses in­side his body are pre­cisely mir­rored by those in­side mine. The ex­pla­na­tion of his claims ob­vi­ously does not de­pend on the ex­is­tence of con­scious­ness, as there is no con­scious­ness in his world. It fol­lows that the ex­pla­na­tion of my claims is also in­de­pen­dent of the ex­is­tence of con­scious­ness.

Chalmers is not ar­gu­ing against zom­bies; those are his ac­tual be­liefs!

This para­dox­i­cal situ­a­tion is at once delight­ful and dis­turb­ing. It is not ob­vi­ously fatal to the nonre­duc­tive po­si­tion, but it is at least some­thing that we need to come to grips with...

I would se­ri­ously nom­i­nate this as the largest bul­let ever bit­ten in the his­tory of time. And that is a back­handed com­pli­ment to David Chalmers: A lesser mor­tal would sim­ply fail to see the im­pli­ca­tions, or re­fuse to face them, or ra­tio­nal­ize a rea­son it wasn’t so.

Why would any­one bite a bul­let that large? Why would any­one pos­tu­late un­con­scious zom­bies who write pa­pers about con­scious­ness for ex­actly the same rea­son that our own gen­uinely con­scious philoso­phers do?

Not be­cause of the first in­tu­ition I wrote about, the in­tu­ition of the quiet in­ner listener. That in­tu­ition may say that zom­bies can drive cars or do math or even fall in love, but it doesn’t say that zom­bies write philos­o­phy pa­pers about their quiet in­ner listen­ers.

No, the drive to bite this bul­let comes from an en­tirely differ­ent in­tu­ition—the in­tu­ition that no mat­ter how many atoms you add up, no mat­ter how many masses and elec­tri­cal charges in­ter­act with each other, they will never nec­es­sar­ily pro­duce a sub­jec­tive sen­sa­tion of the mys­te­ri­ous red­ness of red. It may be a fact about our phys­i­cal uni­verse (Chalmers says) that putting such-and-such atoms into such-and-such a po­si­tion, evokes a sen­sa­tion of red­ness; but if so, it is not a nec­es­sary fact, it is some­thing to be ex­plained above and be­yond the mo­tion of the atoms.

But if you con­sider the sec­ond in­tu­ition on its own, with­out the in­tu­ition of the quiet listener, it is hard to see why ir­re­ducibil­ity im­plies zom­bie-ism. Maybe there’s just a differ­ent kind of stuff, apart from and ad­di­tional to atoms, that is not causally pas­sive—a soul that ac­tu­ally does stuff. A soul that plays a real causal role in why we write about “the mys­te­ri­ous red­ness of red”. Take out the soul, and… well, as­sum­ing you just don’t fall over in a coma, you cer­tainly won’t write any more pa­pers about con­scious­ness!

This is the po­si­tion taken by Descartes and most other an­cient thinkers: The soul is of a differ­ent kind, but it in­ter­acts with the body. Descartes’s po­si­tion is tech­ni­cally known as sub­stance du­al­ism—there is a thought-stuff, a mind-stuff, and it is not like atoms; but it is causally po­tent, in­ter­ac­tive, and leaves a visi­ble mark on our uni­verse.

Zom­bie-ists are prop­erty du­al­ists—they don’t be­lieve in a sep­a­rate soul; they be­lieve that mat­ter in our uni­verse has ad­di­tional prop­er­ties be­yond the phys­i­cal.

“Beyond the phys­i­cal”? What does that mean? It means the ex­tra prop­er­ties are there, but they don’t in­fluence the mo­tion of the atoms, like the prop­er­ties of elec­tri­cal charge or mass. The ex­tra prop­er­ties are not ex­per­i­men­tally de­tectable by third par­ties; you know you are con­scious, from the in­side of your ex­tra prop­er­ties, but no sci­en­tist can ever di­rectly de­tect this from out­side.

So the ad­di­tional prop­er­ties are there, but not causally ac­tive. The ex­tra prop­er­ties do not move atoms around, which is why they can’t be de­tected by third par­ties.

And that’s why we can (allegedly) imag­ine a uni­verse just like this one, with all the atoms in the same places, but the ex­tra prop­er­ties miss­ing, such that ev­ery atom moves the same as be­fore, but no one is con­scious.

The Zom­bie World might not be phys­i­cally pos­si­ble, say the zom­bie-ists—be­cause it is a fact that all the mat­ter in our uni­verse has the ex­tra prop­er­ties, or obeys the bridg­ing laws that evoke con­scious­ness—but the Zom­bie World is log­i­cally pos­si­ble: the bridg­ing laws could have been differ­ent.

But why, oh why, say that the ex­tra prop­er­ties are epiphe­nom­e­nal and un­de­tectable?

We can put this dilemma very sharply: Chalmers be­lieves that there is some­thing called con­scious­ness, and this con­scious­ness em­bod­ies the true and in­de­scrib­able sub­stance of the mys­te­ri­ous red­ness of red. It may be a prop­erty be­yond mass and charge, but it’s there, and it is con­scious­ness. Now, hav­ing said the above, Chalmers fur­ther­more speci­fies that this true stuff of con­scious­ness is epiphe­nom­e­nal, with­out causal po­tency—but why say that?

Why say that you could sub­tract this true stuff of con­scious­ness, and leave all the atoms in the same place do­ing the same things? If that’s true, we need some sep­a­rate phys­i­cal ex­pla­na­tion for why Chalmers talks about “the mys­te­ri­ous red­ness of red”. That is, there ex­ists both a mys­te­ri­ous red­ness of red, which is ex­tra-phys­i­cal, and an en­tirely sep­a­rate rea­son, within physics, why Chalmers talks about the “mys­te­ri­ous red­ness of red”.

Chalmers does con­fess that these two things seem like they ought to be re­lated, but why do you need to as­sert two sep­a­rate phe­nom­ena? Why not just as­sert one or the other?

Once you’ve pos­tu­lated that there is a mys­te­ri­ous red­ness of red, why not just say that it in­ter­acts with your in­ter­nal nar­ra­tive and makes you talk about the “mys­te­ri­ous red­ness of red”?

Isn’t Descartes tak­ing the sim­pler ap­proach, here? The strictly sim­pler ap­proach?

Why pos­tu­late an ex­tra­ma­te­rial soul, and then pos­tu­late that the soul has no effect on the phys­i­cal world, and then pos­tu­late a mys­te­ri­ous un­known ma­te­rial pro­cess that causes your in­ter­nal nar­ra­tive to talk about con­scious ex­pe­rience?

Why not pos­tu­late the true stuff of con­scious­ness which no amount of mere me­chan­i­cal atoms can add up to, and then, hav­ing gone that far already, let this true stuff of con­scious­ness have causal effects like mak­ing philoso­phers talk about con­scious­ness?

I am not en­dors­ing Descartes’s view. But at least I can un­der­stand where Descartes is com­ing from. Con­scious­ness seems mys­te­ri­ous, so you pos­tu­late a mys­te­ri­ous stuff of con­scious­ness. Fine.

But now the zom­bie-ists pos­tu­late that this mys­te­ri­ous stuff doesn’t do any­thing, so you need a whole new ex­pla­na­tion for why you say you’re con­scious.

That isn’t vi­tal­ism. That’s some­thing so bizarre that vi­tal­ists would spit out their coffee. “When fires burn, they re­lease phlo­gis­ton. But phlo­gis­ton doesn’t have any ex­per­i­men­tally de­tectable im­pact on our uni­verse, so you’ll have to go look­ing for a sep­a­rate ex­pla­na­tion of why a fire can melt snow.” What?

Are prop­erty du­al­ists un­der the im­pres­sion that if they pos­tu­late a new ac­tive force, some­thing that has a causal im­pact on physics, they will be stick­ing their necks out too far?

Me, I’d say that if you pos­tu­late a mys­te­ri­ous, sep­a­rate, ad­di­tional, in­her­ently men­tal prop­erty of con­scious­ness, above and be­yond po­si­tions and ve­loc­i­ties, then, at that point, you have already stuck your neck out. To pos­tu­late this stuff of con­scious­ness, and then fur­ther pos­tu­late that it doesn’t do any­thing—for the love of cute kit­tens, why?

There isn’t even an ob­vi­ous ca­reer mo­tive. “Hi, I’m a philoso­pher of con­scious­ness. My sub­ject mat­ter is the most im­por­tant thing in the uni­verse and I should get lots of fund­ing? Well, it’s nice of you to say so, but ac­tu­ally the phe­nomenon I study doesn’t do any­thing what­so­ever.”

Chalmers is one of the most frus­trat­ing philoso­phers I know. He does this re­ally sharp anal­y­sis… and then turns left at the last minute. He lays out ev­ery­thing that’s wrong with the Zom­bie World sce­nario, and then, hav­ing re­duced the whole ar­gu­ment to smithereens, calmly ac­cepts it.

Chalmers does the same thing when he lays out, in calm de­tail, the prob­lem with say­ing that our own be­liefs in con­scious­ness are jus­tified, when our zom­bie twins say ex­actly the same thing for ex­actly the same rea­sons and are wrong.

On Chalmers’s the­ory, Chalmers say­ing that he be­lieves in con­scious­ness can­not be causally jus­tified; the be­lief is not caused by the fact it­self, like look­ing at an ac­tual real sock be­ing the cause of why you say there’s a sock. In the ab­sence of con­scious­ness, Chalmers would write the same pa­pers for the same rea­sons.

On epiphe­nom­e­nal­ism, Chalmers say­ing that he be­lieves in con­scious­ness can­not be jus­tified as the product of a pro­cess that sys­tem­at­i­cally out­puts true be­liefs, be­cause the zom­bie twin writes the same pa­pers us­ing the same sys­tem­atic pro­cess and is wrong.

Chalmers ad­mits this. Chalmers, in fact, ex­plains the ar­gu­ment in great de­tail in his book. Okay, so Chalmers has solidly proven that he is not jus­tified in be­liev­ing in epiphe­nom­e­nal con­scious­ness, right? No. Chalmers writes:

Con­scious ex­pe­rience lies at the cen­ter of our epistemic uni­verse; we have ac­cess to it di­rectly. This raises the ques­tion: what is it that jus­tifies our be­liefs about our ex­pe­riences, if it is not a causal link to those ex­pe­riences, and if it is not the mechanisms by which the be­liefs are formed? I think the an­swer to this is clear: it is hav­ing the ex­pe­riences that jus­tifies the be­liefs. For ex­am­ple, the very fact that I have a red ex­pe­rience now pro­vides jus­tifi­ca­tion for my be­lief that I am hav­ing a red ex­pe­rience...

Be­cause my zom­bie twin lacks ex­pe­riences, he is in a very differ­ent epistemic situ­a­tion from me, and his judg­ments lack the cor­re­spond­ing jus­tifi­ca­tion. It may be tempt­ing to ob­ject that if my be­lief lies in the phys­i­cal realm, its jus­tifi­ca­tion must lie in the phys­i­cal realm; but this is a non se­quitur. From the fact that there is no jus­tifi­ca­tion in the phys­i­cal realm, one might con­clude that the phys­i­cal por­tion of me (my brain, say) is not jus­tified in its be­lief. But the ques­tion is whether I am jus­tified in the be­lief, not whether my brain is jus­tified in the be­lief, and if prop­erty du­al­ism is cor­rect than there is more to me than my brain.

So—if I’ve got this the­sis right—there’s a core you, above and be­yond your brain, that be­lieves it is not a zom­bie, and di­rectly ex­pe­riences not be­ing a zom­bie; and so its be­liefs are jus­tified.

But Chalmers just wrote all that stuff down, in his very phys­i­cal book, and so did the zom­bie-Chalmers.

The zom­bie Chalmers can’t have writ­ten the book be­cause of the zom­bie’s core self above the brain; there must be some en­tirely differ­ent rea­son, within the laws of physics.

It fol­lows that even if there is a part of Chalmers hid­den away that is con­scious and be­lieves in con­scious­ness, di­rectly and with­out me­di­a­tion, there is also a sep­a­rable sub­space of Chalmers—a causally closed cog­ni­tive sub­sys­tem that acts en­tirely within physics—and this “outer self” is what speaks Chalmers’s in­ter­nal nar­ra­tive, and writes pa­pers on con­scious­ness.

I do not see any way to evade the charge that, on Chalmers’s own the­ory, this sep­a­rable outer Chalmers is de­ranged. This is the part of Chalmers that is the same in this world, or the Zom­bie World; and in ei­ther world it writes philos­o­phy pa­pers on con­scious­ness for no valid rea­son. Chalmers’s philos­o­phy pa­pers are not out­put by that in­ner core of aware­ness and be­lief-in-aware­ness, they are out­put by the mere physics of the in­ter­nal nar­ra­tive that makes Chalmers’s fingers strike the keys of his com­puter.

And yet this de­ranged outer Chalmers is writ­ing philos­o­phy pa­pers that just hap­pen to be perfectly right, by a sep­a­rate and ad­di­tional mir­a­cle. Not a log­i­cally nec­es­sary mir­a­cle (then the Zom­bie World would not be log­i­cally pos­si­ble). A phys­i­cally con­tin­gent mir­a­cle, that hap­pens to be true in what we think is our uni­verse, even though sci­ence can never dis­t­in­guish our uni­verse from the Zom­bie World.

I think I speak for all re­duc­tion­ists when I say Huh?

That’s not epicy­cles. That’s, “Plane­tary mo­tions fol­low these epicy­cles—but epicy­cles don’t ac­tu­ally do any­thing—there’s some­thing else that makes the planets move the same way the epicy­cles say they should, which I haven’t been able to ex­plain—and by the way, I would say this even if there weren’t any epicy­cles.”

Ac­cord­ing to Chalmers, the causally closed sys­tem of Chalmers’s in­ter­nal nar­ra­tive is (mys­te­ri­ously) malfunc­tion­ing in a way that, not by ne­ces­sity, but just in our uni­verse, mirac­u­lously hap­pens to be cor­rect. Fur­ther­more, the in­ter­nal nar­ra­tive as­serts “the in­ter­nal nar­ra­tive is mys­te­ri­ously malfunc­tion­ing, but mirac­u­lously hap­pens to be cor­rectly echo­ing the jus­tified thoughts of the epiphe­nom­e­nal in­ner core”, and again, in our uni­verse, mirac­u­lously hap­pens to be cor­rect.

Oh, come on!

Shouldn’t there come a point where you just give up on an idea? Where, on some raw in­tu­itive level, you just go: What on Earth was I think­ing?

Hu­man­ity has ac­cu­mu­lated some broad ex­pe­rience with what cor­rect the­o­ries of the world look like. This is not what a cor­rect the­ory looks like.

“Ar­gu­ment from in­cre­dulity,” you say. Fine, you want it spel­led out? The said Chalmer­sian the­ory pos­tu­lates mul­ti­ple un­ex­plained com­plex mir­a­cles. This drives down its prior prob­a­bil­ity, by the con­junc­tion rule of prob­a­bil­ity and Oc­cam’s Ra­zor. It is there­fore dom­i­nated by at least two the­o­ries which pos­tu­late fewer mir­a­cles, namely:

  • Sub­stance du­al­ism:

    • There is a stuff of con­scious­ness which is not yet un­der­stood, an ex­traor­di­nary su­per-phys­i­cal stuff that visi­bly af­fects our world; and this stuff is what makes us talk about con­scious­ness.

  • Not-quite-faith-based re­duc­tion­ism:

    • That-which-we-name “con­scious­ness” hap­pens within physics, in a way not yet un­der­stood, just like what hap­pened the last three thou­sand times hu­man­ity ran into some­thing mys­te­ri­ous.

    • Your in­tu­ition that no ma­te­rial sub­stance can pos­si­bly add up to con­scious­ness is in­cor­rect. If you ac­tu­ally knew ex­actly why you talk about con­scious­ness, this would give you new in­sights, of a form you can’t now an­ti­ci­pate; and af­ter­ward you would re­al­ize that your ar­gu­ments about nor­mal physics hav­ing no room for con­scious­ness were flawed.

Com­pare to:

  • Epiphe­nom­e­nal prop­erty du­al­ism:

    • Mat­ter has ad­di­tional con­scious­ness-prop­er­ties which are not yet un­der­stood. Th­ese prop­er­ties are epiphe­nom­e­nal with re­spect to or­di­nar­ily ob­serv­able physics—they make no differ­ence to the mo­tion of par­ti­cles.

    • Separately, there ex­ists a not-yet-un­der­stood rea­son within nor­mal physics why philoso­phers talk about con­scious­ness and in­vent the­o­ries of dual prop­er­ties.

    • Mirac­u­lously, when philoso­phers talk about con­scious­ness, the bridg­ing laws of our world are ex­actly right to make this talk about con­scious­ness cor­rect, even though it arises from a malfunc­tion (draw­ing of log­i­cally un­war­ranted con­clu­sions) in the causally closed cog­ni­tive sys­tem that types philos­o­phy pa­pers.

I know I’m speak­ing from limited ex­pe­rience, here. But based on my limited ex­pe­rience, the Zom­bie Ar­gu­ment may be a can­di­date for the most de­ranged idea in all of philos­o­phy.

There are times when, as a ra­tio­nal­ist, you have to be­lieve things that seem weird to you. Rel­a­tivity seems weird, quan­tum me­chan­ics seems weird, nat­u­ral se­lec­tion seems weird.

But these weird­nesses are pinned down by mas­sive ev­i­dence. There’s a differ­ence be­tween be­liev­ing some­thing weird be­cause sci­ence has con­firmed it over­whelm­ingly—

—ver­sus be­liev­ing a propo­si­tion that seems down­right de­ranged, be­cause of a great big com­pli­cated philo­soph­i­cal ar­gu­ment cen­tered around un­speci­fied mir­a­cles and gi­ant blank spots not even claimed to be un­der­stood—

—in a case where even if you ac­cept ev­ery­thing that has been told to you so far, af­ter­ward the phe­nomenon will still seem like a mys­tery and still have the same qual­ity of won­drous im­pen­e­tra­bil­ity that it had at the start.

The cor­rect thing for a ra­tio­nal­ist to say at this point, if all of David Chalmers’s ar­gu­ments seem in­di­vi­d­u­ally plau­si­ble, is:

“Okay… I don’t know how con­scious­ness works… I ad­mit that… and maybe I’m ap­proach­ing the whole prob­lem wrong, or ask­ing the wrong ques­tions… but this zom­bie busi­ness can’t pos­si­bly be right. The ar­gu­ments aren’t nailed down enough to make me be­lieve this—es­pe­cially when ac­cept­ing it won’t make me feel any less con­fused. On a core gut level, this just doesn’t look like the way re­al­ity could re­ally re­ally work.”

But this is not what I say, for I don’t think the ar­gu­ments are plau­si­ble. “In gen­eral, all odd num­bers are prime” looked “con­ceiv­able” when you had only thought about 3, 5, and 7. It stopped seem­ing rea­son­able when you thought about 9.

Zom­bies looked con­ceiv­able when you looked out at a beau­tiful sun­set and thought about the quiet in­ner aware­ness in­side you watch­ing that sun­set, which seemed like it could van­ish with­out chang­ing the way you walked or smiled; obe­di­ent to the plau­si­ble-sound­ing gen­er­al­iza­tion, “the in­ner listener has no outer effects”. That gen­er­al­iza­tion should stop seem­ing pos­si­ble when you say out loud, “But wait, I am think­ing this thought right now in­side my au­di­tory cor­tex, and that thought can make my lips move, trans­lat­ing my aware­ness of my quiet in­ner listener into a mo­tion of my lips, mean­ing that con­scious­ness is part of the min­i­mal clo­sure of causal­ity in this uni­verse.” I can’t think of any­thing else to say about the con­ceiv­abil­ity ar­gu­ment. The zom­bies are dead.