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24.09 spring 061

24.09 Minds and Machinesspring 2006

• evaluations and finalexam questions nextmonday

• the knowledge argument,contd.

• Levine on theexplanatory gap

24.09 spring 062

Minds and Machinesspring 2006

the knowledgeargument

24.09 spring 063

“Epiphenomenal qualia”

• sets out the “knowledge argument” againstphysicalism

• physicalism is the thesis “that all (correct)information is physical information”

• that is, more or less, all facts are physical facts

• but it’s clearer to understand physicalism in theway explained before, as a supervenience thesis

24.09 spring 064

black-and-white Mary

• “Mary is a brilliant scientist…forcedto investigate the world from ablack and white room via a blackand white television monitor”

• she “acquires, let us suppose, all thephysical information there is toobtain when we see ripetomatoes…use terms like‘red’…and so on”

• “what will happen when Mary isreleased from her black and whiteroom?”

24.09 spring 065

“Will she learnanything or not?”

24.09 spring 066

“It just seems obvious thatshe will learn somethingabout the world and ourexperience of it…But shehad all the physicalinformation.Ergo…Physicalism is false”

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24.09 spring 067

the knowledge argument1 imprisoned Mary knows all the physical facts

hence:2 if physicalism is true, Mary (before her release) knows all

the facts3 after her release, Mary learns something–something she

couldn’t have known while imprisoned4 if Mary learns something, she learns a fact

hence (from 3, 4):5 Mary learns a fact

hence (from 2, 5):6 physicalism is false

24.09 spring 068

the knowledge argumentJackson draws a further conclusion

7 our experiences have “qualia”

(“The whole thrust of the knowledge argument is thatMary...does not know about certain qualia…” (“What Marydidn’t know”))

Qualia are “certain [nonphysical]features of bodily sensations [and]perceptual experiences...the hurtfulnessof pains, the itchiness of itches [etc.]”

• contrast Tye’s “qualia” and “Qualia”

24.09 spring 069

the move from 1 to 21 imprisoned Mary knows all the physical facts

hence:2 if physicalism is true, Mary (before her release) knows all

the facts

rationale: not knowing something is not being able to decidebetween rival possibilities—in other words not being able to tellwhat possible world one is in; so if imprisoned Mary doesn’tknow something then she can’t tell exactly what possible worldshe is in; but if physicalism is true she plainly can tell whatpossible world she in, because if physicalism is true then thetotality of the physical facts eliminates all possibilities but one,and she knows all the physical facts

24.09 spring 0610

Mary, Fred, and the bat

• “It is important to distinguish [Nagel’s argument] fromthe Knowledge argument”

• “I was not complaining that we weren’t finding outwhat it is like to be Fred, I was complaining that thereis something about his experience, a property of it, ofwhich we were left ignorant…No amount ofknowledge about Fred, be it physical or not, amountsto knowledge “from the inside” concerning Fred” but this is a bit unfair: “The point of view in question is not

one accessible only to a single individual. Rather it is a type.”(p. 222)

24.09 spring 0611

Mary, Fred, and the bat

• only Fred can know (what he would expressby saying) “It is I myself who is…”o but: Nagel thinks we don’t know something

about the general kind of experience enjoyed bybats, not that we don’t know what Bill the batknows when he says “It is I myself who is…”

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self-locating knowledgeexplained

• only Fred can know (what he would express by saying)“It is I myself who is…” (see also Lewis, “The ThirdWay”, 283)

• one can (apparently) know exactly which possible worldone is in without knowing (what one would express bysaying) “It is I myself who is in 32-124” (etc.)

you arehere

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24.09 spring 0613

resisting the knowledgeargument

1 imprisoned Mary knows all the physical factshence:

2 if physicalism is true, Mary (before her release) knows allthe facts

3 after her release, Mary learns something–something shecouldn’t have known while imprisoned

4 if Mary learns something, she learns a facthence (from 3, 4):

5 Mary learns a facthence (from 2, 5):

6 physicalism is false

24.09 spring 0614

option A: deny 11 imprisoned Mary knows all the physical facts

• not really necessary to suppose Mary knows allthe physical facts

• why would you need special experiences toknow some physical facts?

24.09 spring 0615

option B: resist the move from 1 to 21 imprisoned Mary knows all the physical facts

hence:2 if physicalism is true, Mary (before her release) knows all

the facts• motivation: might superchemist Sally (who knows all the

facts about the distribution of H2O) still be ignorant ofthe fact that water comes out of taps?

• yet that wouldn’t show that there are two worlds alike intheir distribution of H2O that differ in their distributionof water (i.e. that “H2O-ism” is false)

• see Chalmers, “Consciousness and…”, for a reply

24.09 spring 0616

option C: deny 33 after her release, Mary learns something–something she

couldn’t have known while imprisoned

• after all, it’s a pretty weird case to wrap your mindaround

• “It is of course true that in any realistic, readilyimaginable version of the story, Mary would come tolearn something, but in any realistic, readily imaginableversion she might know a lot, but she would not knoweverything physical” (Dennett, Consciousness Explained)

• see also Dennett, “What Robomary knows”

24.09 spring 0617

option D: deny 4

4 if Mary learns something, she learns a fact

Mary learns, but she doesn’t learn a fact:rather, she acquires “know-how”, andthereby an ability (an ability to remember,imagine and recognize the experience ofseeing something red) (see Lewis, “Whatexperience teaches”)

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knowledge-how and knowledge-that

• Ryle argued that “knowledge-how” (e.g. knowinghow to swim) is not reducible to “knowledge-that” (e.g. knowing that kicking one’s legs makesone swim faster)

• does Mary really just acquire “know-how”?• after all, it looks as if she could express her new

knowledge she leaves the room by saying “Aha!,I didn’t know before that seeing red is like this,but now I do know that seeing red is like this”

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24.09 spring 0619

Minds and Machinesspring 2006

Levine and theexplanatory gap

24.09 spring 0620

“Materialism and qualia:the explanatory gap”

• Levine’s position is similar to Nagel’s: physicalismis (or may well be) true, but we don’t understandhow it’s true

• Levine arrives at this conclusion by“transform[ing] Kripke’s argument from ametaphysical one into an epistemological one”

• Levine would accuse Jackson of “transforming anepistemological argument into a metaphysicalone”

24.09 spring 0621

“Materialism and qualia:the explanatory gap”

• Kripke argues that pain ≠ c-fibers firing (a“metaphysical” conclusion)

• Levine thinks this argument does not work, but arelated argument shows that “psycho-physicalidentity statements leave a significant explanatorygap”

• although Levine’s argument does not show thatphysicalism is false, it does “constitute a problemfor materialism”

24.09 spring 0622

• according to Levine, psychophysical identities (e.g‘pain=c-fibers firing’) are “gappy”, unlike others(e.g. ‘heat=mke’)

• he thinks the gappiness of psychophysicalidentities is due to the absence of certain“conceptual” truths

• …and that the absence of such truths is shown byKripke’s argument against the identity theory

24.09 spring 0623

argument K21. if I can clearly and distinctly conceive a proposition p to

be true, then p is possible2. I can clearly and distinctly conceive that there is pain

without c-fiber firing (and vice versa)—that is, I canclearly and distinctly conceive that the proposition thatpain=c-fiber firing is not true

therefore:3. there is a possible world in which pain is not c-fiber firing

(it is not necessarily true that pain=c-fiber firing)

4. if it’s true that pain=c-fiber firing, then it is necessarilytrue

therefore (from 3, 4):5. pain is not c-fiber firing

24.09 spring 0624

Levine’s objection: deny (1)1. if I can clearly and distinctly conceive a proposition p to betrue, then p is possible

“Since epistemological possibility [i.e. clear anddistinct conceivability] is not sufficient formetaphysical possibility, the fact that what isintuitively contingent turns out to be metaphysicallynecessary should not bother us terribly. It’s to beexpected.”

o one might think this reply is a bit dismissive—surelyconceivability is a good guide to possibility, so why does itfail in this case? (see Nagel’s note 11 and the paper by Hillfor one suggestions)

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24.09 spring 0625

Minds and Machinesspring 2006

read Stoljar forwednesday