What You Don’t Know CanHurt You1

karen bennett

Cornell University

This boy is Ignorance. This girl is Want. Beware them both, and all oftheir degree, but most of all beware this boy, for on his brow I see thatwritten which is Doom... —Charles Dickens, A Christmas Carol

Daniel Stoljar’s Ignorance and Imagination: The Epistemic Origin of the

Problem of Consciousness is a lively and interesting contribution to

recent debates about the nature of phenomenal experience. Stoljar

defends what he calls the epistemic view—roughly, the view that the

knowledge argument and the conceivability argument (henceforth,

the KA and CA) seem plausible because we are ignorant of some of

the physical facts, not because the physical facts fail to determine the

phenomenal facts. As Stoljar notes (p. 9), other people have suggested

versions of this view. But he articulates it more clearly and defends it

more thoroughly. He disentangles the main theses of the epistemic view

from optional extras, like Colin McGinn’s claim that our ignorance is

intractable, and provides a detailed diagnosis of just how ignorance

undermines the KA and CA. Ignorance and Imagination is clear and

economical, and you will learn a great deal from reading it even if you

are not in the end convinced.

The epistemic view is the conjunction of two claims. The first is that

what Stoljar calls the ‘ignorance hypothesis’ is true: we are ignorant of

a type of experience-relevant nonexperiential truth. The second is that

our ignorance solves the logical problem of experience by undermining

the KA and CA. We are ignorant, and the fact that we are ignorant

explains our susceptibility to those arguments even though every expe-

riential truth is in fact entailed by nonexperiential truths. In particular,

1 Thanks to Torin Alter, David Orr, and Derk Pereboom for detailed comments, and

to participants in my spring 2007 graduate seminar at Princeton for discussion of

some early ideas about the book.

766 KAREN BENNETT

Philosophy and Phenomenological ResearchVol. LXXIX No. 3, November 2009� 2009 Philosophy and Phenomenological Research, LLC

Philosophy andPhenomenological Research

our ignorance renders it likely that we are making one of the ‘standard

mistakes’ in modal reasoning—mode confusion, proposition confusion,

and ⁄or defeater neglect.Stoljar’s example of the slugs and the tiles provides a clear illustra-

tion of a way in which ignorance might impair a creature’s modal rea-

soning. Imagine a community of slugs that lives on a mosaic made of

triangular tiles and tiles shaped like curve-edged ‘pieces of pie’. The

slugs can only perceive the triangular tiles, and as a consequence are

mystified by the presence of circles in the mosaic. How can the circles

be accounted for in non-circular terms? Indeed, many slugs believe that

there could be a mosaic indiscernible from the actual mosaic in all

non-circular respects, but which lacks circles. Clearly, they are wrong

about that, and Stoljar diagnoses their error as follows. The slugs can

strongly conceive a world just like the actual world with respect to all

the non-circular truths that they know about—namely, the triangular

ones—but without circles. And they can (at best) weakly conceive a

world just like the actual world with respect to all the non-circular

truths, but without circles. But neither of those conceivings is enough

to justify their belief that a ‘zombie mosaic’ is possible—only the latter

proposition conceived in the former way would be enough. So much,

then, for the slug’s version of the CA. Because they suffer from what

Stoljar calls ‘basic-level ignorance,’ they are in no position to trust their

modal reasoning about the relationship between the tiles and the cir-

cles.

For simplicity, I will continue to focus on the CA in what follows,

but I believe that what I say will apply, mutatis mutandis, to the KA. I

will explore three ideas. First, I will introduce the second type of igno-

rance that Stoljar discusses, and suggest that his treatment of this

‘intermediate-level ignorance’ is unclear, and may commit him to a

priori physicalism. Second, I will examine the notion of ‘experience-

relevance’ invoked in the ignorance hypothesis, and argue that it may

allow Stoljar to make the dialectically advantageous claim that the CA

is a bad argument even if dualism is true. Third, I will point out that

his strategy generalizes beyond arguments like the CA and KA. I will

close with some questions this raises, particularly about just how plau-

sible it must be that we are ignorant in the ways Stoljar suggests.

1. What is Intermediate-Level Ignorance, and how Would it Impair ourModal Reasoning?

Stoljar thinks ignorance comes in (at least) two forms. Basic-level igno-

rance is ‘‘ignorance of a truth concerning a particular element of nature

or a basic fact of the world’’ (72); intermediate-level ignorance is

BOOK SYMPOSIUM 767

‘‘ignorance of a truth that is not itself basic but is determined by the

basic facts’’ (72). However, Stoljar says little to establish that interme-

diate-level ignorance can be a source of modal error independently of

basic-level ignorance. If it cannot be, Stoljar has inadvertently commit-

ted himself to a priori physicalism—the claim that the experiential con-

ditional, which takes all the basic physical truths as antecedent and

yields the experiential truths as consequent, is a priori.

Let me begin with a clarification. Having used the tile-dwelling slugs

to describe basic-level ignorance, Stoljar illustrates intermediate-level

ignorance with a story about moths that inhabit an array of light

beams. But it is not clear that this second example is as useful. (Full

disclosure: this is probably my fault, as he attributes the story to me.)

The moths, we are told, know about red, green, and yellow light, but

mistakenly think that all three are basic because they don’t know that

yellow light is the product of green and red light. They are ‘‘ignorant

of the principles whereby various lights combine to create different col-

ored beams’’ (73). But this suggests that the moths are ignorant of a

fundamental law governing the interaction of fundamental entities, and

thus that they suffer from basic-level ignorance after all. Because the

example is somewhat problematic, I will set the moths aside, and focus

upon the official definition of intermediate-level ignorance. Consider a

set of basic entities, properties, and laws, C, whose existence and distri-

bution entails the existence and distribution of a set of distinct entities,

properties, and laws B, whose existence and distribution in turn entails

the existence and distribution of a set of distinct entities, properties,

and laws A. For someone to suffer from intermediate-level ignorance

but not basic-level ignorance is for her to know all the C-truths, but

not all the B-truths.

The question is this: can intermediate level ignorance be an indepen-

dent source of modal error? If so, it must be possible for someone—call

him ‘Iggy’—to know all the C-truths, not to know all the B-truths, and

to mistakenly believe it possible for a world to be just like the actual

world with respect to all the C-truths, but different with respect to the

A-truths. We also need to say that it is Iggy’s ignorance of some B-

truths that leads him into this modal error—that his ignorance leads

him to make one of the ‘standard mistakes’. Whatever the exact form

of the mistake, it will presumably have its source in the fact that he

cannot represent the B-truths of which he is ignorant. That is, when he

tries to conceive a world that is just like the actual world with respect

to the C-truths, he neglects some of the B-truths that would have to

hold there, and this in turn leads him to neglect some of the A-truths.

But now we are in a position structurally indiscernible from the one in

which we started. We have simply explained one modal error in terms

768 KAREN BENNETT

of another. Instead of merely asking why he mistakenly thinks it possi-

ble for the A-truths to vary independently of the C-truths, we now

need to ask why he mistakenly thinks it possible for the B-truths to

vary independently of the C-truths.

So how can we explain away Iggy’s apparent ability to conceive a

world just like the actual world with respect to the C-truths, but differ-

ent with respect to the B-truths? There are two possible answers. Either

he is ignorant of some of the C-truths after all—in which case we can

insert Stoljar’s story about modal error ‘chez slug’—or else there is

some alternate explanation. But Stoljar does not offer us any alternate

explanation, and, indeed, takes the former route. His treatment of the

CA and KA ‘chez moth’ falls back upon an appeal to basic-level igno-

rance. In the case of the CA, he suggests that the most the moths are

strongly conceiving is that ‘‘there is an array identical to the actual

array in respect of most red and green truths, but which is different

from it in respect of some yellow truths’’ (85, emphasis added); in the

case of the KA, he suggests that the moths are only strongly conceiving

that ‘‘a logically omniscient and conceptually sophisticated supermoth

knows most of the red and green truths of the array and learns the yel-

low truths on the basis of experience’’ (86, emphasis added).

Clearly, none of that shows that intermediate-level ignorance does

require basic-level ignorance. My point is rather that Stoljar gives us

no reason to think otherwise—and some reason to think that he thinks

that it does. If so, though, he is committed to a priori physicalism.

Why? Because if intermediate-level ignorance requires basic-level igno-

rance, simple contraposition means that full basic-level knowledge

would bring with it full intermediate-level knowledge. That is, anyone

who knew all the basic-level truths would also know everything they

entail. The lesson for the special case of physicalism is clear. If physi-

calism is true, as Stoljar thinks, the experiential conditional is not only

true but a priori.

Officially, however, Stoljar is neutral on the question of a priori

vs. a posteriori physicalism—indeed, one of the potentially most

interesting claims of the book is that recent debates about the episte-

mic status of the experiential conditional are misguided. On his view,

it does not matter whether that conditional is a priori or a posteri-

ori. All that matters is the diagnosis of the mistake(s) in the CA

and KA. The most plausible diagnosis, he claims, is that offered by

the epistemic view, which can be conjoined with either a priori or a

posteriori physicalism (chapters 9 and 10). But if he wants to main-

tain this neutrality, he owes us a story about how intermediate-level

ignorance can be an independent source of modal error—or, at least,

a story about how intermediate-level ignorance can occur without

BOOK SYMPOSIUM 769

basic-level ignorance. Some passing remarks in chapter 7 (esp. p.

131) suggest that he indeed thinks that such a situation can occur,

but he does not explain it, and it plays no role in his explicit treat-

ment of the CA and KA ‘chez moth’.

2. The Ignorance Hypothesis and the Dualist

Physicalists sometimes respond to the CA and KA in ways that

explicitly presuppose physicalism, or at any rate in ways that would

not begin to persuade a committed dualist. That is fine for purely

defensive purposes. But one interesting feature of Stoljar’s response

is that it offers the possibility of more—it offers the possibility of a

response that does not presuppose physicalism, and thus should be

of real concern to dualists as well. Now, let me be clear that

Stoljar’s own overall position is that that physicalism is true,2 and

that our ignorance blinds us to this fact. However, the particular

story that he tells about how our ignorance undermines the CA—the

particular diagnosis of mixed confusion that he offers the slugs—

need not presuppose physicalism.

The ignorance hypothesis, recall, says that we are ignorant of a type

of experience-relevant nonexperiential truth. But what does ‘experience-

relevant’ mean? Stoljar defines it analogously to an INUS condition,

saying that ‘‘one truth T is relevant to a truth T* just in case T is an

essential part of a set of truths that together entail T*’’ (70). The ques-

tion that immediately arises in the case at hand is whether or not the

unknown nonexperiential T must be an essential part of a set of nonex-

periential truths. That is, contrast two versions of the ignorance

hypothesis:

W(eak): we are ignorant of a type of nonexperiential truth

that, either alone or together with the known truths, entails the

experiential truths.

S(trong): we are ignorant of a type of nonexperiential truth

that, either alone or together with the known nonexperiential

truths, entails the experiential truths.

S is much stronger, for it entails the truth of physicalism and W does

not. Now, Stoljar of course believes S, because he believes both W and

2 Or, at least, that ‘non-experientialism’ is true—he thinks that all experiential truths

are entailed by nonexperiential ones. Those who believe (as I do not) that protopsy-

chism is both a) a viable option, and b) a nonphysicalist form of non-experiential-

ism, can substitute ‘non-experientialism’ for my uses of ‘physicalism’ in all of what

follows.

770 KAREN BENNETT

physicalism. But it seems to me that his treatment of the CA chez slug

only requires W—or, more precisely, that W does as well as S, in the

sense that if S successfully undermines the CA in the way that Stoljar

suggests, W does too. This is dialectically important. It means that the

ignorance-based attack on the CA need not assume physicalism, for

although dualists will deny S, they should find W plausible.

Most dualists, after all, do think that the experiential truths are

entailed. They just think that the set of truths that entail them must

include not only nonexperiential truths, but also fundamental psycho-

physical linking laws—contingent connections between a person’s phe-

nomenal states and the physical things that go on in her brain. And

presumably we might be ignorant not only of the full nature of those con-

nections, but of the nature of the physical states involved. That is, we

might be ignorant of some neuroscientific details that figure prominently

in Chalmers-style fundamental psychophysical laws.3 As a result, even

dualists should find W plausible—well, as plausible as physicalists

should, anyway (see the next section)—and W will do Stoljar’s job as well

as S does. To see this, suppose that both dualism and W really are true;

we are ignorant in the way I just sketched. Stoljar’s criticism of the CA

proceeds as before. The claim would be that although we can strongly

conceive an experientially different world that is just like the actual world

with respect to all currently known nonexperiential truths, we can at best

weakly conceive an experientially different world that is just like the

actual world with respect to all the nonexperiential truths. By assump-

tion, we have no idea what all the nonexperiential truths are. Just as in

the case of the slugs, though, neither of those conceivings is good enough

to justify the belief that a zombie world is possible—even if it really is.

In short, if (really, if—the claim is a conditional one) S is enough to

generate the diagnosis of the mixed error of proposition confusion and

mode confusion, so is W. This suggests that even committed dualists

should drop the CA.

3. How Generally can Appeals to Ignorance be Used?

The book has one curious lacuna: Stoljar does not address whether

variations on the epistemic view might apply elsewhere in philosophy.

Can appeals to ignorance be used to undermine other sorts of philo-

sophical arguments? Stoljar does explicitly argue that a virtue of his

view is that it does not impugn all conceivability arguments—for exam-

ple, it leaves the perfect actor argument against behaviorism untouched

3 Are such psychophysical laws genuinely ‘nonexperiential’ in the relevant sense?

Interestingly, that is the one substantive term in the ignorance hypothesis that Stol-

jar does not define (68–72).

BOOK SYMPOSIUM 771

(52–53, 168). But to say that it does not overgeneralize to other con-

ceivability arguments is not to say that it does not overgeneralize at all.

Indeed, the appeal to ignorance can be characterized broadly enough

to make it a weapon against all sorts of arguments.

Here is the general recipe, for a target argument that has a series of

premises P1 through Pn:

a) argue that it is plausible to suppose that we are ignorant of the

truth (and perhaps the content) of some proposition p, and

b) argue that our ignorance of p undermines our reason for

believing some Pi.

Call this the Generalized Ignorance Strategy, or GIS.

Is GIS a good recipe? I don’t know. Properly answering the ques-

tion requires doing some epistemology, and clarifying the notions of

plausibility, justification, and ignorance in play. For example, note

that ignorance of p is not the same as ignorance of whether or not

p. It is much easier to argue that I am plausibly ignorant of the

latter than the former. I am definitely ignorant of whether or not

Barack Obama is wearing a tie right now, but I have no idea

whether I am ignorant of the fact that Barack Obama is wearing a

tie right now, precisely because I have no idea whether it is a fact.

My ignorance of p itself—i.e., my ignorance of the fact that p—

entails the truth of p. Consequently, rendering plausible that I am

ignorant of p requires rendering plausible that p. I have formulated

GIS so that it requires this harder task, which seems correct (or at

least in line with Stoljar’s discussion). But this in turn raises ques-

tions about the required notion of plausibility. How much does it

take to show that it is plausible that I am ignorant of p—or the

entailed claim that it is plausible that p?

We can distinguish between a strong and weak notion of plausibility,

corresponding to the strong and weak notions of conceivability that

play a large role in Stoljar’s discussion (75):

p is weakly plausible if we are not certain that �p.

p is strongly plausible if we have positive reason to believe p.

Even this sketchy distinction constitutes some progress, for GIS is

probably not a good recipe if ‘plausible’ is read as ‘weakly plausible’.

Consider two quick examples.

772 KAREN BENNETT

First, it is weakly, though not strongly, plausible that I am ignorant

of the fact that a meteor has destroyed my house since I left this morn-

ing. That is, I am not certain that I am not ignorant in this way,

because I am not certain that a meteor has not destroyed my house.

Would this ignorance undermine my reason for believing that my

house remains standing?

Second, consider the problem of evil. A simple version relies upon

the following two premises:

1. If there is a God, s ⁄he is perfect: omniscient, omnipotent,

and omnibenevolent.

2. No perfect being would permit as much suffering as there is.

A familiar response says that it is a mistake to think that God’s exis-

tence is inconsistent with suffering, because we have no idea what sorts

of trade-offs a perfect being would make. This is at heart an instance

of GIS, with p = God’s Grand Plan, and Pi = the second premise.

Now, it is certainly weakly plausible that we are ignorant of this p. We

are not certain that God does not have a Grand Plan that renders

apparently pointless suffering consistent with His perfection; it remains

an open epistemic possibility that he does. But is this by itself enough

to dissolve the problem of evil? Surely not. Surely we also need at least

the beginnings of a positive story about how and why a perfect being

might permit suffering. This, of course, is precisely what professional

philosophers typically offer, as they argue that suffering makes possible

certain higher order goods, and so forth.4

But if anything in this ballpark is correct—if proper application of

GIS requires more than weak plausibility—then we must return to the

specific case at hand. Just how plausible has Stoljar rendered the igno-

rance hypothesis in the chapter he devotes to the task (Chapter 5)? Or,

given my discussion in the previous section, just how plausible has he

rendered what version? Showing that S is strongly plausible would

require providing positive reason to believe that physicalism is true,

and Stoljar’s arguments in Chapter 5 do not do this.5 Thus if he agrees

with my suggestion that strong plausibility is required, he should also

agree with my earlier suggestion that S is not. So has he shown that W

is strongly plausible? Perhaps. The question is whether his appeals to

our ‘‘excessive optimism’’ (§5.2 and 5.3), the unfinished state of neuro-

4 For an excellent discussion of theists’ appeals to ignorance to solve the problem of

evil, see Pereboom 2005.5 Note: he does provide brief arguments for physicalism in Chapter 2, but this is not

in the context of defending the ignorance hypothesis.

BOOK SYMPOSIUM 773

science (§5.6), and the explanatory power of the ignorance hypothesis

(§5.7) really provide positive reason to believe that we are ignorant of a

type of experience-relevant nonexperiential truth, or whether they sim-

ply make salient the thought that we cannot be certain that we are not.

If I am right that GIS requires more than the latter skeptical concern,

further defense of the ignorance hypothesis cannot hurt.

I have raised more questions than I have answered. Under what con-

ditions do appeals to ignorance have force? How exactly should GIS

be formulated? I wish Stoljar had raised these sorts of issues, both

because they are of independent interest, and because the answers to

them affect the status of his own epistemic view. That view is intrigu-

ing, and a real contribution to the philosophy of mind. It should be

taken seriously by both physicalists and dualists alike—but just how

seriously depends, largely, on the sorts of questions I have gestured at

in this final section.

References

Stoljar, Daniel. 2006. Ignorance and Imagination: The Epistemic Source

of the Problem of Consciousness. Oxford: Oxford University Press.

Pereboom, Derk. 2005. ‘‘The Problem of Evil,’’ in William E. Mann,

ed. The Blackwell Guide to the Philosophy of Religion. Oxford:

Blackwell, 148–170.

774 KAREN BENNETT