Mary's Room is a poor argument for Dualism.

Mary is a bril­liant sci­en­tist who is, for what­ever rea­son, forced to inves­ti­gate the world from a black and white room via a black and white tele­vi­sion mon­i­tor. She spe­cialises in the neu­ro­phys­i­ol­ogy of vision and acquires, let us sup­pose, all the phys­i­cal infor­ma­tion there is to obtain about what goes on when we see ripe toma­toes, or the sky, and use terms like ‘red’,’ ‘blue’, and so on. She dis­cov­ers, for exam­ple, just which wave-length com­bi­na­tions from the sky stim­u­late the reti­na, and exactly how this pro­duces via then cen­tral ner­vous sys­tem the con­trac­tion of the vocal chords and expul­sion of air from the lungs that results in the utter­ing of the sen­tence ‘The sky is blue’. [..] What will hap­pen when Mary is released from he black and white room or is given a colour tele­vi­sion mon­i­tor? Will she learn any­thing or not? It seems just obvi­ous that she will lean some­thing about the world and our visual expe­ri­ence of it. But then it is inescapable that her pre­vi­ous knowl­edge was incom­plete. But she had all the phys­i­cal infor­ma­tion. Ergo there is more to have than that, and Phys­i­cal­ism is false.

…So goes the famous Mary’s Room thought experiment. This is an argu­ment, for­mu­lated by philoso­pher Frank Jackson intended to dis­prove the doc­trine of Physicalism.12 One of the most famous and thorny top­ics in the his­tory of the phi­los­o­phy of mind is the sub­ject of dualism. That is, are human beings sim­ply phys­i­cal beings or is the mind at least partly non-­phys­i­cal. In other words, do peo­ple have souls or are we just brains sub­ject to the lim­i­ta­tions of the phys­i­cal world. Dualism, attributed to thinkers as diverse as Plato and Renee Descartes, is the doc­trine that the mind is non-­phys­i­cal, that there is a dual­ity between the body and the mind. Its oppo­site, would be physicalism, the doc­trine that every­thing that exists, includ­ing the mind, is phys­i­cal, and can ulti­mately be reduced to physics. This later stance is by far the more pop­u­lar stance in the mod­ern day.

Argu­ments for phys­i­cal­ism regard­ing the mind usu­ally rest on the intu­ition that the mind and its oper­a­tions seem to at last be partly syn­ony­mous with the brain which is clearly a phys­i­cal organ. Phys­i­cal­ists tend to look at the suc­cess of mod­ern sci­ence and its abil­ity to explain for­merly inex­plica­ble things in terms of phys­i­cal laws and intuit that phys­i­cal laws can prob­a­bly also explain things that we don’t yet have a full sat­is­fac­tory expla­na­tion of, such as the mind. How­ev­er, there are still mod­ern day dual­ists, many of whom believe that there is some­thing inef­fa­ble in human con­scious­ness that just can’t be cap­tured with a phys­i­cal­ist expla­na­tion. One pop­u­lar appeal that such philoso­phers make is to qualia, the details of sub­jec­tive con­scious expe­ri­ence and how, intu­itive­ly, accord­ing to them, it does­n’t make sense that qualia can exist in purely phys­i­cal terms.

One such philoso­pher was Frank Jack­son, a self described “qualia freak”, who believed that qualia could be used as part of an argu­ment to refute phys­i­cal­ism. His paper, Epiphenomenal Qualia was an attempt to make such an argu­ment and one of the cen­tral parts of that paper was the Mary’s Room thought exper­i­ment cited above. Mary’s Room has proved to be a very pop­u­lar argu­ment for mod­ern dual­ists, in part because it’s easy to under­stand, but I don’t think that it is a very good one.

The Argument from Qualia

At its heart, Mary’s Room is an argu­ment that there are more kinds of knowl­edge than just phys­i­cal knowl­edge. When Jack­son orig­i­nally wrote his paper, he took phys­i­cal­ism to be the stance that, “the the­sis of Phys­i­cal­ism” is “that all (cor­rect) infor­ma­tion is phys­i­cal infor­ma­tion.” But Jack­son dis­agree with this stance. He believed that there was another kind of infor­ma­tion, the kind of infor­ma­tion that one got from direct sense expe­ri­ence that was not express­ible in terms of mere physics. As he put it:

Tell me every­thing phys­i­cal there is to tell about what is going on in a liv­ing brain, the kinds of states, their func­tional roles, their rela­tion to what goes on at other times and in other brains, and s an and so forth, and be I as clever as can be in fit­ting it all togeth­er, you won’t have told be about the hurt­ful­ness of pains, the itch­i­ness of itch­es, pangs of jeal­ousy, or about the char­ac­ter­is­tic expe­ri­ence of tast­ing a lemon, smelling a rose, hear­ing a load noise or see­ing the sky.

If noth­ing else, Jack­son’s point of view here is quite poet­ic, so it’s easy to see its appeal. There is some­thing inef­fa­ble about the expe­ri­ence of tast­ing a lemon that just can’t be expressed in a purely phys­i­cal descrip­tion of the process. These things that Jack­son talks about, whether it is the hurt­ful­ness of pains or the itch­i­ness of itches are qualia, sub­jec­tive con­scious expe­ri­ences, and the exis­tence of these qualia, he argues, demon­strate that not every kind of knowl­edge is about some­thing phys­i­cal.

Think about Mary, who we described above. For what­ever rea­son, while she has been allowed to learn every­thing there is to know about color vision, she has never been allowed to actu­ally expe­ri­ence color vision and so she lacks a cer­tain kind of knowl­edge, the knowl­edge of what it is like see col­or. Another philoso­pher, John Locke (a dual­ist) once noted:

Sup­pose a child had the use of his eyes till he knows and dis­tin­guishes colours; but then cataracts shut the win­dows, and he is forty or fifty years per­fectly in the dark; and in that time per­fectly loses all mem­ory of the ideas of colours he once had. This was the case of a blind man I once talked with, who lost his sight by the smal­l­-pox when he was a child, and had no more notion of colours than one born blind. I ask whether any one can say this man had then any ideas of colours in his mind, any more than one born blind? And I think nobody will say that either of them had in his mind any ideas of colours at all. His cataracts are couched, and then he has the ideas (which he remem­bers not) of colours, DE NOVO, by his restored sight, con­veyed to his mind, and that with­out any con­scious­ness of a for­mer acquain­tance. And these now he can revive and call to mind in the dark.

In other words, the idea of color is some­thing that must be experienced; it can­not sim­ply be described. No phys­i­cal descrip­tion, it would seem, no mat­ter how com­plete, repli­cates that expe­ri­ence. And that expe­ri­ence is itself a kind of knowl­edge.


There are a num­ber of dif­fer­ent kinds of response to Jack­son’s argu­ment. Some of them hinge on the idea that with enough infor­ma­tion maybe Mary could under­stand what it was like to see color even if she had never done it before, but I think the most com­pelling coun­ter­ar­gu­ment is to point out that Jack­son’s argu­ment is not actu­ally against phys­i­cal­ism at all. Recall Jack­son’s definition: Phys­i­cal­ism is the the­sis “that all (cor­rect) infor­ma­tion is phys­i­cal infor­ma­tion.” This isn’t actu­ally what phys­i­cal­ists believe. What phys­i­cal­ists believe is that everything that exists is phys­i­cal, which is a dif­fer­ent propo­si­tion alto­geth­er.

Let’s say that Mary does learn some­thing when she is first exposed to col­or. Before she expe­ri­enced color for the first time she was given all of the infor­ma­tion pos­si­ble about the physics of color and about the physics of the brain which result in the expe­ri­ence of col­or, but had never expe­ri­enced color her­self. Upon expe­ri­enc­ing color for the first time she now knows what it’s like to expe­ri­ence col­or. This later knowl­edge is not knowl­edge about the physics of some­thing, but the knowl­edge itself is nev­er­the­less phys­i­cal.

What do I mean by that? Well, if we accept for the sake of argu­ment the phys­i­cal­ist posi­tion that every­thing in the mind includ­ing knowl­edge and expe­ri­ence reduces to dif­fer­ent brain-s­tates or groups of brain-s­tates, then Mary’s expe­ri­ence of col­or, at least the way it expresses itself in her mind, is noth­ing other that a par­tic­u­lar brain-s­tate which is phys­i­cal. In other words, her expe­ri­ence is a phys­i­cal thing that hap­pens, regard­less of whether her knowl­edge is of physics per-se.

Let’s take another way of look­ing at this for a sec­ond. Let’s say you wanted to learn how to hit a base­ball, You could try read­ing up on the physics of hit­ting a base­ball, learn­ing about how grav­ity and the wind resis­tance work on the ball as it trav­els through the air, about the mechan­ics of the body as you swing the bat, about what the proper form is and why it makes it pos­si­ble to hit the ball, etc but all the read­ing in the world by itself will not let you hit a base­ball on the first try. The moment you get up from your read­ing and actu­ally try to hit a ball, you will prob­a­bly miss. How­ev­er, after prac­tic­ing hit­ting a ball, and after swing­ing the bat many, many times at any, many balls, you will prob­a­bly improve to the point where you can actu­ally start hit­ting balls with some reg­u­lar­i­ty. The rea­son is that there is a dif­fer­ence in know­ing about some­thing and expe­ri­ence in doing the thing.

What hap­pens when you prac­tice hit­ting a base­ball? Well, like, a lot. Your mus­cles, nerves, and brain work together to develop a pro­file of what it feels like to swing the bat cor­rectly and hit a base­ball. Each par­tic­u­lar posi­tion of the body, and each tran­si­tion between those stances has a par­tic­u­lar feel. In addi­tion, the motions that the body must go through in order swing a bat require a coor­di­nated motion of the mus­cles that must be coor­di­nated with con­tin­u­ously updat­ing infor­ma­tion about the loca­tion and motion of the ball. When you prac­tice hit­ting a base­ball, the brain learns these feel­ings, motions, etc and con­nects them together in the loco­mo­tor por­tion of the brain. The nerves, mus­cles, and brain, all change so that the par­tic­u­lar task of hit­ting a base­ball can be done with­out engag­ing the higher por­tions of the brain. Much of the process auto­mat­ic, as far as the prac­ti­tioner is con­cerned. This is very dif­fer­ent from what hap­pens when you sim­ply read about how hit­ting a ball works. Dif­fer­ent parts of the brain are engaged when you learn about some­thing than when you actu­ally do some­thing. Both of these things can be called “knowl­edge” but they are dif­fer­ent things being given the same name; they are dif­fer­ent types of “knowl­edge.”

This ulti­mately is the dis­tinc­tion that is being made in the Mary’s Room thought exper­i­ment. The term “knowl­edge” is being used to refer indis­crim­i­nately to brain-s­tates but isn’t cap­tur­ing the dis­tinc­tion between high­er-order “book” knowl­edge which cap­tures the rela­tion­ships between idea and lower order expe­ri­en­tial knowl­edge which relates dif­fer­ent sense expe­ri­ences together gen­er­at­ing what we call “qualia” and which also helps to relate those qualia to the high­er-order ideas. When Mary stud­ies physics, she expands her “book” knowl­edge, but when she steps into the world and sees color for the first time, she expands her expe­ri­en­tial knowl­edge. In nei­ther case is it nec­es­sary that some­thing non-­phys­i­cal is hap­pen­ing.

High­er-order ideas, so called “book” knowl­edge can be about phys­i­cal things. It can also be about physics per-se. It can be about non-­phys­i­cal things, or about things that don’t exist. But none of that has any­thing to do with whether the knowl­edge itself is some­thing physical; whether it is sim­ply a brain state or there is some­thing extra-­phys­i­cal going on. Some­thing sim­i­lar is true with expe­ri­en­tial knowledge; whether the sub­ject mat­ter of knowl­edge is some­thing phys­i­cal is a dif­fer­ent ques­tion from whether the knowl­edge itself is phys­i­cal. Expe­ri­ence can be a phys­i­cal process even if it can’t sim­ply be derived from a suf­fi­cient under­stand­ing of physics.


So that’s the famous Mary’s Room argu­ment and my pre­ferred respon­se. There are actu­ally a lot of other responses to this argu­ment, the major­ity of mod­ern philoso­phers are phys­i­cal­ists. Even Frank Jack­son has since aban­doned epiphe­nom­e­nal­ist stance he was argu­ing for when he first advanced his thought exper­i­ment. This might be sur­pris­ing because physicalism vs dualism is a big debate in west­ern phi­los­o­phy and the most famous philoso­phers have his­tor­i­cally been on the dualist side of the debate. That changed over the past cen­tury or two with the decline of the influ­ence of Chris­tian­ity and the rise of more sec­u­lar schools of phi­los­o­phy. Mary’s Room and the argu­ment from qualia was a bit of a rear­guard action by Jack­son and other sur­viv­ing dual­ists, defend­ing a philo­soph­i­cal stance that has been los­ing ground for quite a while now.

  1. Physicalism is the idea that everything that exists is physical. This is a rather vague statement. If it helps physicalism, in practice, is usually used as a synonym for materialism and for the purposes of the Mary’s Room thought experiment, that’s probably good enough. However, there is a slight difference between materialism and physicalism. Historically, materialism is associated with the beliefs of the ancient Greek Atomists such as Democrites and Epicurus. The ancient Greeks, and the early modern philosophers who were influenced by them, attempted explain reality in terms of the motions of microscopic particles called “atoms” this is before the modern discovery of atoms by modern physics, and the motion and interaction of these atoms. The ancient atomists didn’t believe in things like gravity or other physical forces, and consequently, classical understandings of materialism don’t account for those sorts of things. Modern physics is therefor incompatible with materialism as classically conceived, but physicalism doesn’t have that problem. Physicalism reduces things to physics even if physics itself isn’t reducible to matter. 

Last update: 18/10/2023

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