Imaginability as a Guide to Possibility

Imaginability as a Guide to Possibility Peter Kung Pomona College Draft 03-03-2005 for C&P seminar, please do not circulate Hume asserts in the Treatise: “’Tis established maxim in metaphysics, That whatever the mind clearly conceives includes the idea of possible existence, or in other words, that nothing we imagine is absolutely impossible” (I.ii.2). Hume is certainly right about this much: we presume it to be an established maxim. We take ourselves to have some knowledge of what could be, or what could have been, in the sense of metaphysical possibilities. Hume does not tell us, however, how this “established maxim” has been established, and, the more we scrutinize the maxim, the more it cries out for explanation. Two questions stand out. The what question asks: What, precisely, is it to conceive something? And the why question adds: Why is it that conceiving, so understood, provides evidence for possibility? Because “conceive” is a word with many senses, there are many ways to answer the what question. But each of these senses is clearly unsuitable to play the epistemological role of evidence for possibility. 1 Merely understanding, thinking or entertaining a proposition is obviously insufficient, for it is easy enough to understand, think, or entertain thoughts about what is necessarily false. The same goes for assuming, supposing, and taking for granted. Finding a proposition believable — true for all you know for certain, or possibly true for all you know for certain — is inadequate, because on ignorance about what is true or what is possible cannot be evidence for possibility. Some philosophers, present author included, find imaginability a more promising type of conceivability. Imagining a proposition is one way, and perhaps the only way, of conceiving a proposition that is modally probative. 2 In this paper I will argue that sensory imagination, imagination that involves mental imagery — seeing a dragon in the mind’s eye, hearing in your mind’s ear the dragon’s mellifluous voice — is an important source of evidence for possibility. There are two typical responses to the claim that imaginability is evidence for possibility: Skepticism. Imagination does not provide evidence for possibility. We should dispense with imagination in our modal epistemology, and embrace either a general modal skepticism or another source of modal evidence.

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Tidman 1994 and Yablo 1993 have very helpful discussions of these various candidates for conceivability, and their inability to serve as evidence for possibility. My discussion derives from theirs. 2

Terminological note: an imagining that provides evidence for possibility is a probative imagining, and counts as modal evidence. I shall use these expressions interchangeably.

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It is the power of imagination that drives this skepticism. If imagination is truly as limitless as the poets profess, if we routinely imagine the impossible as well as the possible (unicorns and hippogriffs, water as an element, complete arithmetic, AbdulJabbar battling Alcindor for a rebound, the truth of a cherished but false philosophical theory, and so on), it is not the sort of faculty for which we can reasonably maintain is reliable. It is useless as modal evidence. The second response is non-skeptical: it says that every imagining is evidence for possibility. It overcomes the skeptical challenge by making the striking claim that imagination is less powerful than we thought; we do not and cannot imagine all sorts of crazy, wonderful things. Error Theory. Imagination is always probative, but weak. Contrary to what the poets write, imagination is not an absolute power, it is not boundless. In particular, we do not and cannot imagine anything that is impossible. E.g., if unicorns are impossible, then, despite what we might think, we do not imagine unicorns. We are constrained — though we may not realize it — to imagine only what is possible. This is a surprisingly popular view of imagination. I contend that a close examination of how Saul Kripke treats the famous cases he uses to argue for the existence of a posteriori necessities reveals that he holds the error theory. I regard the error theory as unacceptable. The error theory results when modal epistemological considerations are allowed to dictate what we can and cannot imagine: situation S is impossible, therefore we cannot be imagining situation S; we must be imagining some situation S′ and mistakenly thinking we are imagining S. It may seem like we are imagining, say, a boy traveling back in time in a DeLorean and changing his past, but if it turns out this is impossible, then this cannot be what we are imagining. Modal epistemological considerations force us to conclude that we are frequently wrong about what we take ourselves to be imagining. I hope it strikes the reader that this order of explanation is the reverse of what it should be. We should first develop our account of imagination independently of modal epistemological considerations, and then, with a theory of the imagination in hand, ask whether it is suitable to serve as evidence for possibility. 3 Specifically, we should acknowledge that the imagination has the power and flexibility we typically ascribe to it, and confront the skeptical challenge head on. I defend a response does just that. Selective View. Imagination is selectively probative, but powerful. There is a principled distinction between probative imaginings, which provide genuine evidence for possibility, and non-probative imaginings, which do not. While imagination may be virtually limitless, so that we can and do imagine the impossible, these impossible imaginings fall squarely on the non-probative side of the partition.

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Others have recommended this methodology as well. See the conclusion of Kind 1996.

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This view better accounts for what we imagine in the influential cases discussed by Kripke; it grants, for example, that we were at one time (and perhaps still are) able to imagine past-changing time travel, water composed of XYZ molecules, or the shocking falsity of Fermat’s Last Theorem. I sketch an account of imagining that distinguishes between basic and assigned contents of imaginings, and use this distinction to spell out independent reasons for classifying some imaginings, including the ones just described, as evidentially valueless. To imagine water composed of XYZ or the falsity of Fermat’s Last Theorem is to imagine impossibilities, but, I argue, they do not provide us with evidence that such things are possible. I develop this view in detail, explain how the theory handles some familiar cases, and reply to a number of objections. Let us begin by considering why we should take imaginings as modal evidence in the first place; why, that is, the skeptical response is unacceptable.

I. Imaginings as Modal Evidence The core notion of imagination I am interested in is sensory imagining, imagining that involve mental imagery. The guiding thought is that sensory imagination is evidentially like perception: perceptual experiences are prima facie evidence for how the world actually is; imaginative experiences are prima facie evidence for how the world could be. What can be said in defense of sensory imagination as a source of modal evidence? (As before, the qualification “sensory” should be understood in all references to imagination. We will discuss non-sensory imaginings briefly at the end of the paper.) To begin, we can note that when we imagine things being a certain way, it is simply intuitive that this act of mind, the imagining, provides evidence for the way things could be. It is simply intuitive that imagining this page is yellow gives me reason to think that the page could have been yellow. This initial response bears affinity to the one dogmatists will give regarding perceptual justification. Dogmatism is the view that, as something of a brute fact, we are prima facie justified in believing that things are as they are presented by our perceptual experiences. In particular, this justification does not depend on our justification for believing anything else. 4 But when we consider what the dogmatist about perceptual justification thinks we are prima facie justified in believing we will see that the modal theorist can defend a modest foundationalist position; she doesn’t have to be all that dogmatic. She can offer a more satisfying explanation of why imaginings are prima facie modal evidence. To make this second point we need a brief summary of our findings on the content of imagining. Some of our conscious experiences — perceptual experiences 4

The only support James Pryor offers for his dogmatist position is: “For a large class of propositions…it’s intuitively very natural to think that having an experience as of that proposition justifies one in believing that proposition to be true. What’s more, one’s justification here doesn’t seem to depend on any complicated justifying argument” (536). Other dogmatists include Alston (1989), Audi (1993), Moore (1939), and perhaps Chisholm (in his later work, e.g., 1988).

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prominently — have a qualitative component, and this qualitative component has basic content. These experiences present in a direct and immediate way certain aspects of the world around us, those aspects that, we might ordinarily say, we are conscious of: they specify the distribution of objects and “observational” properties in three-dimensional (egocentric) space. Observational properties, are, roughly, the traditional primary and secondary properties. 5 In vision, for example, we are consciously presented with three-dimensional space filled with objects of varying colors and shapes. Such basic contents of the qualitative component (or basic qualitative contents) are what, according to dogmatists, confers prima facie justification. Sensory imaginings also have basic qualitative contents. States with basic qualitative content do, intuitively, also provide evidence for possibility. In the perceptual case, the qualitative content of an experience presents a way that space can consistently be filled around the perceiver. When my perceptual experience presents a red surface to my right and a black surface to my left, one of the things that we theorists can say about the experience is that, as far as the experience presents, a red surface on the right is consistent with a black surface on the left. That is one way that space could be filled. Skeptical hypotheses demonstrate this point nicely: suppose I am deceived by an evil demon, and there is no material world. Still, we think, my visual experiences give me evidence of the way the world could be. How I perceive space to be filled is a way that it could be filled, even if it is not in fact filled that way. What goes for the qualitative contents of perceptual experiences also goes for the qualitative contents of imaginative experiences. 6

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Though there is some controversy over the observational/non-observational distinction, I trust that it is clear enough for my purposes here. I am using “observational” as a way of glossing the more complete account I give elsewhere. 6

One way to block the intuition that basic qualitative contents provide reason for possibility is to hold that we infer possibility from actuality; perceptual experiences furnish no evidence for possibility except insofar as can be inferred from actuality. (I.e., we reason: “Experience presents space in way W; the world is such that W; whatever is actual is possible; therefore, way W presents space consistently.”) It strikes me that this confuses conceptual priority with epistemic priority. It may very well be that the concept of truth is more fundamental than the concept of possibility, and possessing the former concept is a prerequisite for acquiring the latter. But it does not follow that perceptual experiences cannot be a basic source of evidence for possibility. (Notice that “x is actual, therefore x is possible” cannot be the only introduction rule for the concept of possibility. If it were, we could not judge that something is possible without first judging it is actual.) I think that is the more plausible view; and in fact I am inclined toward an even stronger line of reasoning: perceptual experience must provide evidence for possibility for it to provide evidence of actuality. Given that we know a priori that the actual world is consistent, if we had no reason to think that the way space is presented by experience is consistent, that would undermine experience’s status as evidence for actuality. All of these issues deserve further investigation. Note that if the claim that basic qualitative contents provide evidence for possibility is rejected, I can fall back to dogmatism. It still is intuitive that imagining this page is yellow gives me reason to think that the page could have been yellow, and we can simply take this as a brute fact that admits of no further explanation.

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These two points furnish us with positive reason to take imaginings as prima facie evidence for possibility. Our epistemological starting point is that imagining provides prima facie modal evidence; this starting point suffices to answer a common class of objections. The reader may already have thought: What about the waterfall illusion (Crane 1988)? What about Escher drawings? The qualitative content of seeming to perceive or imagining, e.g., four continuous connected ascending staircases, as is depicted in Escher’s drawings, fails to present consistently filled space. While this is true, let us ask ourselves whether the existence of such illusions in the perceptual case means that we no longer take perceptual experience as a prima facie guide to actuality. The answer is no. Escher-type illusions are the exception rather than the rule. 7 Prima facie evidence is fallible evidence; our imaginative experiences are a fallible guide to possibility, just as perceptual experiences are a fallible guide to actuality. All the familiar issues regarding fallibilism transfer from the perceptual to the imaginative. 8 Accepting the existence of fallible evidence means one cannot simply complain that when you imagine P, you might be wrong; for all you know P is impossible. Imaginative experience is supposed to be evidence for possibility. As with any fallible evidence, one could have the evidence and yet have it turn out that the evidence is misleading. It does not follow, we ordinarily think, that you have to rule out (especially not in advance) that your evidence is misleading. Now the issue of what we need to rule out in advance is the subject of much recent debate, and is at the root of very deep skeptical worries. However, I am not attempting a solution to skepticism here. I take as my starting point that having evidence does not require ruling out in advance that the evidence is not misleading, and rest content if modal epistemology turns out to be on a par with perceptual epistemology when it comes to this kind of skeptical worry. The real question, then, is whether we have reason to think modal errors happen regularly, that they are the rule, rather than the exception. The determined skeptic will still think the answer is yes. The skeptic reminds us of the power of imagination, and our facility in imagining impossibilities, even known impossibilities, as a reason to doubt that imagination is evidence for possibility. The power and flexibility of imagination is due largely to assignments. Assignments are contents of imaginings beyond the basic qualitative contents; they come in two varieties. The first is labels. The various objects, regions, surfaces, and so on presented by the basic qualitative content come already categorized; they have conceptual contents already assigned. In imagining Dick Cheney, I conjure up a certain mental image. The image depicts a figure who appears a certain way, and this figure is simply imagined as Dick Cheney. This requires no activity on my part — I don’t have to recognize the figure depicted — because the figure in the image comes pre-labeled with the concept . The imagining of Cheney will have a 7

While I do not want to rest my case on it, there is some psychological evidence that standard illusions, such as the Ponzo illusion, cannot be reproduced in imagination. See Reisberg & Morris 1985. 8

The following discussion of fallibilism draws from Yablo 1993: §§V–VI.

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great many other labels: the large round object is labeled , the protuberance on the head is labeled <nose>, and so on. These labels encapsulate quite a bit of information. If the oi are objects presented by the mental image (“object” should be understood quite loosely, to include regions, stuffs, events, etc. as well as proper objects), then the label content might be: that o1 is F; that o2 is F and o2 is G; that o3 is F and o3 is G. The second additional kind of content, stipulations or stipulative content, is propositional content that goes above and beyond that of the mental image. Background stipulations do not reference anything in the mental image; they fill in background information about the imagined situation. Stipulations that make claims about objects in the mental image that are not depicted by the image are foreground stipulations. Assignments, or assigned contents, is our loose way of referring to all information captured by labels and stipulations; any piece of this information is an assignment. Assigned content covers background stipulations and the labels and foreground stipulations made about the objects presented by the mental image. It also covers whether these labels and foreground stipulations are made of the same or distinct objects; e.g., whether the labels and are assigned to a single object or two distinct objects. The strategy for answering the skeptic will be to stress how it is assignments that permit us to imagine the impossible. If we carefully proscribe the role of assignments, then imagination can still serve as evidence for possibility. And we can do this while acknowledging imagination’s limitlessness. Before we come to the details of the proposal, however, we need first to examine an alternative reply to the skeptic, the error theory. I hope the reader will think for a moment about how spectacular we ordinarily take the imagination to be, so that in considering the error theorists’ claims that it is a rather more paltry faculty constrained by what is possible, it is plain just how implausible this really is.

II. Kripkean Error Theory In the opening of this paper, I described the error theory, the view that imagination is always probative, but weak. I argue that Kripke holds this view, articulated and further elaborated in a particularly clear way by Stephen Yablo. 9 On this view every imagining is prima facie evidence for possibility. The challenge for this view is to explain away apparent counterexamples, that is, to explain away the cases in which it seems as if we imagine something impossible. For if it turns out that we regularly imagine the impossible, this cannot simply be chalked up to imagination’s fallibility — regular error would legitimate the “but maybe I’m wrong” doubts we dismissed above. The Kripke-Yablo response is to argue that we do not really imagine impossibilities: in these cases, we imagine a possible situation that is similar enough to the impossibility to be mistaken for it.

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Yablo 1993; see also his 1990 and 2000.

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Most of us have so internalized the Kripkean story about a posteriori necessities that it is difficult to recall those heady days when we encountered the ideas for the first time. But let us try to remember what that was like. Take Eddie as one of the uninitiated. Eddie has not given a lot of thought to scientific identities, composition, and origins, but if pressed, he would be inclined to say that they are contingent. What happens when Eddie imagines water being something other than H2O, Muhammed Ali asking Cassius Clay for words that rhyme with “knockout,” or this table not being composed of molecules? Some of Kripke’s remarks suggest that Eddie is not imagining the impossible. But whatever we imagine counterfactually having happened to [the table] other than what actually did, one thing we cannot imagine happening to this thing is that it, given that it is composed of molecules, should still have existed and not have been composed of molecules. We can imagine having discovered that it wasn’t composed of molecules. But once we know that this is a thing composed of molecules — that this is the very nature of the substance of which it is made — we can’t then, at least if the way I see it is correct, imagine that this thing might have failed to have been composed of molecules. (Kripke 1980: 126–27, underlining added)

The point is also put in terms of an incorrect description of the imagined situation. Eddie imagines a situation and then misdescribes it as one where water = XYZ, where Clay is not Ali, where this table is not composed of molecules. However you understand the point, this proposal amounts to a kind of error theory: either the situation we actually imagine is not the one we take ourselves to imagine, or we misapply our concepts in describing the situation we imagine. 10 The Kripkean strategy is really only satisfying if construed as an error theory. Commentary on Kripke’s notion of epistemic possibility and other philosophers’ closely related notion of considering a situation as actual sometimes obscures this, because it alleged that, though we may mistake genuine (metaphysical) possibility for mere epistemic possibility, we really do imagine the epistemic possibilities. 11 No error theory applies to our imaginings of epistemic possibilities; as for mistaking epistemic possibility for metaphysical possibility, it is quite understandable if ordinary folk fail to appreciate that kind of technical philosophical distinction. This cannot be, and is not, the Kripkean view. A proposition is epistemically possible if we are unable to rule it out relative to some epistemic standard: the proposition is true for all we are justified in believing, or for all we know, or for all we know for certain. Kripke suggests that if in imagining “appropriate qualitatively identical evidential situations, an appropriate corresponding qualitative statement might have been [true]” (142), then the statement is epistemically possible. Thus it is 10

I think the error theory is the right interpretation of the cases Kripke discusses; see his diagnosis of what is really going on when we imagine the non-identity of Hesperus and Phosphorus (102–03), Queen Elizabeth as the Trumans’ daughter (112–13), and heat without molecular motion (131–32). However, Kripke does not offer a general theory of imagination, so it is open to him to accept the error theory for the cases he discusses and a different theory for other cases. 11

David Chalmers (1996: 60; 2002: §3, 156–59) is one philosopher who employs the notion of considering a situation as actual.

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epistemically possible that water is XYZ because (roughly) we can imagine having the same evidence (or indistinguishable evidence) that we do now and yet having it “turn out” that water is XYZ. Remember, though, in the Kripkean picture, we cannot imagine the impossible. Thus we cannot really imagine it turning out that water is XYZ. Yablo is explicit: Since it could not have been the case that Hesperus and Phosphorus were distinct, they could not have turned out to be distinct. But, and this is the point, the explanation in terms of imaginability fares no better. To imagine myself truly believing that Hesperus and Phosphorus were distinct, I would have to imagine them being distinct; and that I cannot do, no more than I can imagine Venus being distinct from Venus. (23, underlining added)

Yablo contends we cannot, in any sense, imagine Hesperus distinct from Phosphorus. When we appear to consider an “impossible” situation as actual, what we really do is imagine something closely related that is possible. He continues: Well, I can imagine believing something true with my Hesperus ≠ Phosphorus-thought, for as I said, I can imagine it expressing a proposition with the truth-conditions that Venus ≠ Mars. Since I cannot imagine myself truly believing that Hesperus ≠ Phosphorus, we have uncovered a new kind of conceivability: p is conceivableep [for epistemic possibility] if one can imagine, not truly believing that p (that very proposition!!), but believing something true with one’s actual p-thought. (24, underlining added)

On the Kripke-Yablo picture, we cannot imagine non-H2O water. We can imagine discovering something else, something which, in that situation, would be expressed with the words “water is not H2O.” That is why Kripke speaks of “appropriate corresponding qualitative statement[s]” and Yablo of “believing something true with one’s actual p-thought.” We are imagining a situation in which the word “water” means something other than what it really does, a situation in which there is no water around but only stuff that is called “water” by us. Again, this is the error theory. Think about the natural way to describe something that is, for you, an epistemic possibility. You believe that water is H2O, and probably also that water is necessarily H2O. However, you acknowledge, you might be wrong. For all your evidence, you can imagine being mistaken, imagine discovering that, actually, water is not H2O, imagine it turning out that water is not H2O. In short, you imagine what the Kripkean cannot allow, that, in the actual world, water is not H2O. Thus whether the situation is imagined “as actual” or “as counterfactual,” the Kripkean must say that we do not imagine the impossible situation we take ourselves to imagine. 12, 13

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Chalmers does not, by the criteria I have just articulated, count as a Kripkean. He allows that we can genuinely imagine water is XYZ. Of course he thinks that this is possible, in the relevant sense of possibility (what he calls “primary possibility”). His two-dimensional semantics requires separate treatment because of the special role the a priori plays in modal knowledge.

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Is it not obvious, upon reflection, that the error theory is misguided — or, at the very least, to be avoided if a better explanation is available? Eddie is not confused about what he is imagining. Take the case of Eddie imagining that water is XYZ. He imagines a clear liquid filling the rivers and lakes, falling from the sky, coming out of the taps, etc. He will also stipulate that the liquid has chemical structure XYZ, and that XYZ ≠ H2O. But it is clear that there is one more element to Eddie’s imagining: he imagines the clear liquid as water, the image comes with the label <water> already assigned, just as it does in an ordinary imagining of a glass of water. This is what makes it a case of Eddie imagining that water = XYZ. Or take the case where Eddie imagines Ali asking Clay a question. One figure is imagined as Ali (has the label ) the other is imagined as Clay (has the label ). Is that not how it was with you? You really were imagining XYZ as water; Ali talking to Clay; Twain dying before Clemens; it seems revisionist to suggest otherwise. This applies equally well to imaginings of so-called epistemic possibilities: we imagine (via assignment) being wrong, imagine discovering the world is different than we thought. The Kripkean must deny this. According to the Kripkean, we are not really imagining being wrong, we imagine ourselves thinking slightly different thoughts, ones that, when expressed in words, syntactically appear to contradict our original thoughts, but that do not in fact contradict them. Now this may be the correct description of what is possible. But it is implausible as a description of what we imagine. When I entertain the (epistemic) possibility that Bruce Lee is my father, I imagine that Bruce Lee is my father. Again, it seems revisionist to suggest otherwise. The point is that we should not allow a philosophical preoccupation with modal epistemology to distort our view of imagination. Imaginings are contentful states of mind, and we should be suspicious of any theory that claims we do not really know the contents of our own minds. Kripkeans may be tempted to retreat to the claim that we know the qualitative contents of our mind, but that we sometimes misdescribe those qualitative contents. 14 This seems, in some ways, even worse. If there is anything we are sure about, it is what we stipulate, or what labels are assigned. Recall from §1.3 Wittgenstein’s example: when one imagines King’s College on fire, it does not make sense to ask how we know that it is King’s College one is imagining, and not something else, e.g., a similar-looking part of UCLA, or a miniature replica of the College. If this is right, then the error theory is on the wrong track. Eddie is not mistaking one imagined situation for another, and he is not misdescribing what he 13

I find the difference between “considering as actual” and “considering as counterfactual” to be elusive. The former is clearest when cast in terms of imagining from the inside discovering that suchand-such. It is much more obscure how one is to “consider as actual” a situation imagined from the outside. What is it to imagine as actual a situation where water is XYZ and there are no observers? Is this any different from imagining this situation as counterfactual? I do not have the space to address these questions here. 14

Sometimes Kripke is described as offering a “rephrasal strategy” (see Bealer 1994). “Rephrase” sounds like a euphemism for “correct.” Our initial description of the imagining is incorrect, and hence needs “rephrasing.” Why would it need rephrasing unless it is mistaken?

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does imagine. He is just imagining something that is, in fact, impossible, though he was not aware of the impossibility at the time.

III.

Fragility

I have just argued that, contra Kripke, we can and do imagine the impossible. We now need to answer one more question concerning the nature of imaginings, raised by the last sentence of the previous section. Eddie imagines something that is impossible though he is unaware of the impossibility at the time. Does our ability to imagine the impossible depend on our ignorance of the modal facts? Is our ability to imagine the impossible fragile, in the sense that once we realize something is impossible, we can no longer imagine it? Take Eddie, our subject reading Kripke for the first time. What happens after Eddie reads and accepts Kripke’s story? His modal beliefs change. What can Eddie imagine in light of this new information? There appear to be two alternatives. First, Eddie may find himself still able to imagine situations in which water is XYZ (making all the requisite assignments to do so) while nonetheless believing that such situations are impossible. The second alternative is the fragility claim. The Kripkean error theory is correct for those cases where our modal beliefs are settled. The fragility view offers a promising explanation model for modal error. Ignorance facilitates imagining impossible situations via assignments. When we don’t know whether something is possible, we can, by virtue of our ignorance, make the requisite assignments to imagine it. But these imaginings are fragile. Once we settle our modal beliefs and thereby remove our ignorance, we can no longer imagine the impossibility. This is a psychological generalization, and the thought behind it is something like the following. If Eddie really accepts Kripke’s reasoning, how can he imagine that the stuff composed of XYZ is water? He may be able to imagine a different situation, where XYZ plays the watery role, and where his imagined self is justified in believing that water = XYZ (perhaps because he imagines himself ignorant of the fact that the stuff is XYZ). Nonetheless he will not actually believe of this imagined situation that it is one in which water = XYZ. Imagination always respects modal belief: when one takes oneself to have discovered that something is impossible, that something ceases to be imaginable. 15 Unfortunately, this fragility claim is incorrect. We have already seen one reason to reject it: even once modal beliefs are fixed, the falsity of the proposition 15

The “fragility” label comes from Yablo. Some of his remarks hint that this is his view, but it probably is not. He claims we cannot now imagine Hesperus being distinct from Phosphorus, “ ‘[b]ut we could imagine veridically believing them to be distinct, back when we thought they were distinct.’ True but irrelevant; it remains that Hesperus ≠ Phosphorus is now epistemically possible, but not now conceivable” (1993: 23n48). I interpret Yablo as asserting that the unimaginability of their distinctness was brought about by the discovery that Hesperus is Phosphorus (presumably in the 17th century, with the invention of sufficiently powerful telescopes), and not by Kripke and Putnam’s (1975) more recent 20th century writings. So interpreted, this is the first alternative described in Yablo’s text (though see his remarks on fragility, 1993: §V).

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believed frequently remains epistemically possible. As I argued above, this means imagining being wrong. Let us briefly revisit the issue of epistemic possibility, which will help clarify a point about change in modal belief. A perceptual experience is an “appearance of actuality,” it inclines one towards belief. Similarly, it is suggested that for imagining to be probative, it must involve “appearance of possibility”; it must incline one to believe that P is possible (Yablo 1993: 7). Yablo contends that the appearance of possibility is absent in imagining certain epistemic possibilities. No thought experiment that I, at any rate, can perform gives me the representational appearance of [Goldbach’s] conjecture as possible or as impossible, or the slightest temptation to believe anything about its modal character. (1994: 11)

Why is there no appearance of possibility? According to the error theory, if Goldbach’s conjecture is true, then there is no imagining its falsity, and if it is false, there is no imagining its truth. Yablo seems to be reasoning as follows: symmetry considerations preclude treating apparently imagining Goldbach’s truth differently from apparently imagining Goldbach’s falsehood — the imaginings are subjectively quite similar — so in neither case do we really imagine Goldbach’s truth or Goldbach’s falsehood. What we really imagine is, e.g., being told and becoming convinced that Goldbach’s conjecture is true (or false). If there is no imagining of the truth or falsity of Goldbach’s conjecture, it is no surprise that there is no appearance of possibility. I think this is the right way to interpret Yablo. But suppose for a moment that Yablo allowed that we imagine the truth (or falsity) of Goldbach’s conjecture. Then his contention would be that these imaginings lack the appearance of possibility. But this lack must amount to more than that the imagining does not lead to modal belief, for it is background modal beliefs about the necessity of mathematical truths or falsehoods that prevent the imagining from leading to the belief that Goldbach’s conjecture is possibly true (or false). Our modal beliefs won’t change when we are convinced on other grounds that what we are imagining is necessarily false, or that this imagining is not evidence for possibility. Additionally, it does seem as if, absent our background modal beliefs, we would believe that Goldbach’s conjecture was possibly true (false) upon imagining it. Thus in the absence of the error theory, it is quite mysterious what “appearance of possibility” Goldbach’s imaginings are supposed to lack. And to reiterate, the error theory is simply implausible: when I imagine myself receiving the Fields Medal for proving Goldbach’s conjecture, I imagine — via stipulation — that I really have proved it. I do not imagine any of the details of my proof; I cannot snap out of my daydream and snap my fingers, say “That’s it!” and start writing. Nevertheless, I imagine that Fields Medal–winning journal article contains the proof. This leads to a second reason to reject fragility: even setting aside epistemic possibilities, the fragility claim does not stand up to scrutiny. Notice first that the comparable generalization certainly does not hold of perception: just because we believe (or even know) that something is not the case does not mean that it ceases to perceptually seem to be the case. It may be that in some cases, change in modal beliefs renders certain things unimaginable — and it may very well be that Kripke’s water-

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XYZ is one such case for most people (or, at any rate, most philosophers). 16 But there are cases that show this is not a general rule. When I imagine myself receiving a second Fields Medal for discovering a flaw in Euclid’s proof that there is a largest prime, I am not imagining myself as some kind of charlatan. Again, I imagine — via stipulation — that I really have proved it. We are able to imagine, as we watch Back to the Future (or myriad other movies that involve time travel 17 ), Marty going back to 1955 “the first time,” even if we take this to border on incoherence. Many philosophers (including me) are convinced by Kripke’s arguments that fictional characters and fictional kinds cannot exist, but surely they can still imagine unicorns, Santa Claus, and Smaug the dragon. I am quite confident that my philosophical convictions about fictional characters cause me no trouble in imagining the goings-on at Hogwarts in the latest Harry Potter novel. Thus I think we should reject the fragility claim that imaginability follows modal belief.

IV.

The Problem with Assignments

Let us take stock. The view of imagination I favor claims that imaginings have basic qualitative and assigned content. We have seen how, contra Kripke, assignments allow us to imagine the impossible, and how these assignments allow us a more plausible accounting of Kripke’s famous cases. This is a claim about what we can imagine; we have not yet touched on the issue of whether we are justified in believing that these cases represent genuine possibilities. For all that I have said to this point, Kripke might very well be right about the necessary a posteriori; he might be right, for instance, that water is necessarily H2O. To settle whether Kripke is right, we need to investigate the epistemological ramifications of my view of imagining. Given that we do imagine impossibilities, and indeed that we sometimes can continue to do so after we realize they are impossibilities, are we forced to accept modal skepticism? No, not if we uncover a principled distinction between probative and non-probative imaginings such that the imaginings of the impossible fall squarely on the non-probative side of the partition. An analogy to vision may help illuminate what we are after. Though intuitively perception delivers justified beliefs, we become aware that, on various occasions, our perceptual seemings are inaccurate. We will not know what to make of these inaccuracies — and we might even be led to a general skepticism — unless we can systematize our mistakes by delineating the circumstances in which our visual system is prone to error (poor lighting, high stress, hypnotism, distraction, drugs, etc.). We would especially like an explanation that allows us, with the benefit of hindsight, to identify of those instances in the past when we made mistakes, that such mistakes were likely, or inevitable. (E.g., armed with some understanding of the visual process, we can predict that on those occasions when we wore rose-colors glasses we were likely wrong about the color of objects.) We want something similar in the modal case, to be apprised of those features which

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For an interesting discussion of the difficulty in imagining divergent moral facts, see Gendler

2000. 17

Except, notably, as Pete Graham has emphasized to me, Twelve Monkeys.

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led us to our imagining impossibilities in the past, to better avoid similar mistakes in the present and future. We find such a feature in assignments — both stipulations and labels. Assignments get us into trouble as far as imagining being a guide to possibility; in slogan form: “assignment makes imagining the impossible possible.” Roughly, an imagining that P will not be evidence that P is possible if P’s truth in the imagined situation follows from the assignments alone. 18 Let us see why this is so. In all the cases we have considered thus far in our discussions of the error theory, it is the stipulations and labels that render the situation imagined impossible: one figure is labeled and the other ; the clear stuff is labeled <water> and stipulated to be XYZ; it is stipulated that this writing is a proof of Goldbach’s conjecture. Stipulations and labels are virtually unconstrained. We are able to stipulate or label something in an imagining so long as we find it believable — epistemically possible in the strongest sense that it is true for all we know for certain, or possibly true for all we know for certain. I mean “certainty” in something like the very strong sense that Peter Unger describes: to be certain of a proposition is to have absolutely no doubts at all, it is to be in the very best epistemic position with respect to that proposition. 19 (This is a partly stipulative use of “certain.”) There are very few propositions that are certain in this sense; examples include: that squares have four sides, that bachelors are unmarried, and that modus ponens is a valid inference rule. The falsity of these propositions is, I agree, unimaginable. In this sense of certainty, however, I am not certain that π is an irrational number, because even though at one point I went through the proof, I was never in the very best epistemic position with respect to the proof. I can imagine, via stipulation or label, that π is rational (I might imagine that mathematicians have misled the public, or that the proof contains a subtle error I fail to detect). If the only constraint on stipulations and labels is certainty, this is tantamount to no constraint at all. 20 Let P be some proposition whose possibility we are trying to establish via imagining. The mere fact that we find P (or possibly P) believable, and hence are capable of making the assignments required to make P true in the imagined situation, is not good evidence for P’s possibility. Believability just is lack of certainty. (Let us use “non-certainty” to denote lack of certainty; it avoids the unwanted connotations of “uncertain.”) It would be very odd if our non-certainty counted as evidence of P’s possibility. To be non-certain is to fall short of the very best epistemic position one can be in; how can failing to be in the best epistemic position be evidence for some 18

After the initial formulation of this idea, I discovered that it is also present in Peacocke 1985: §IV, though there it is used primarily in the service of defending a view of the imagination that I call the dependency hypothesis. I regard the dependency hypothesis as unacceptable; see §3.1.1. 19

See Unger 1975: 62–65, 68. Note that the favored expression “true for all you know” does not capture what philosophers typically intend by “believable” or “epistemically possible.” It is not true for all you know that water is not H2O, since, presumably, you do know that water is H2O. 20

Of course propositions about my existence and my present conscious states are certain in the relevant sense, but I can stipulate in an imagining that, e.g., Peter Kung does not exist. So strictly speaking assignments are not even constrained by certainty.

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proposition’s possibility, particularly when we note that total ignorance is one way to fail to be in the best epistemic position? It seems that we need positive evidence for our claims of possibility, and that is exactly what imaginings are supposed to provide. Assignments may merely reflect our less-than-ideal epistemic position. In this regard, assignments are almost as unconstrained as suppositions. Just as we do not take merely supposing that P to be evidence of P’s possibility, stipulating that P or labeling P should similarly not count as evidence for possibility. What goes for each assignment individually goes for what follows from the assignments alone: if it is only by virtue of non-certainty that one is able to assign V1 and assign V2 in the same imagining, and P follows from the conjunction V1 & V2, this imagining does not provide evidence for P’s possibility. On the other hand, suppose we do have other, independent evidence for thinking that P is possible. Then the assignments that make P true in the imagined situation run afoul of a circularity objection. Imagining that P via assignments would be a good guide to P’s possibility only when based on prior information that the assignments, and hence P, is possible. The justification for thinking that P is possible depends on the independent evidence for the assignments; the imagining provides no new evidence. Note the contrast between assigned content and basic qualitative content. The evidentiary value of a qualitative imagining is not undermined by our non-certainty because basic qualitative contents are not so unconstrained. Being in a less-than-ideal epistemic position with respect to a proposition does not thereby enable one to produce a mental image with that proposition as part of its basic qualitative content. For example, suppose you hear a bunch of musicians discussing blue notes, and whether a blue note would sound good in this passage. You know that a blue note is a kind of musical note, but that is the extent of what you know. As a result of your ignorance, you are able to imagine a sound in your mind’s ear and stipulate or label that sound as a blue note. You speculate about the sounds the musicians might be talking about by using your imagination: you imagine various sounds — a mournful minor chord, a high trill — as blue notes. But your ignorance does not itself facilitate your imagining basic-blue-note-qualitative-content, the actual sound of a blue note. (A blue note is the kind of warbling note that Billie Holliday made famous, “a variable microtonal lowering of the third, seventh, and occasionally fifth degrees of the major scale.” 21 ) Basic qualitative contents are not unconstrained the way assigned contents are, and so the concerns about assigned contents do not transfer to basic qualitative contents. As far as basic qualitative contents are concerned, we have no reason to reject the anti-skeptical considerations described in §2.1. What does this mean? If we imagine a situation in which P, where P is simply an assignment, we do not yet have any new evidence that P is possible. We have not yet removed the specter that it is only our non-certainty that is allowing us to so imagine. The same goes for any conjunction of assignments, or anything that follows from the assignments alone. When Eddie imagines a situation, labeling the clear stuff 21

Webster’s Ninth New Collegiate Dictionary.

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<water> and stipulating that the same stuff is XYZ, it follows from these two assignments that in his imagining water = XYZ. It is only by dint of assignment that we are able to imagine an impossible situation like that. It would not strike us as odd that we imagine impossible situations were it not for the philosophical preoccupation with possibility. We have no problem allowing that one can believe a great many necessarily false things (given the diversity of conflicting views in philosophy, a great many philosophers must being doing just that). For some reason, philosophers who want to argue that we do not know as much as we thought about possibility are drawn to making very bold claims about our powers of imagination. For example, Peter Van Inwagen writes: In my view, we cannot imagine worlds in which there are naturally purple cows, time machines, transparent iron, a moon made of green cheese, or pure phenomenal colors in addition to those we know. Anyone who attempts to do so will either fail to imagine a world or else will imagine a world that only seems to have the property of being a world in which the thing in question exists. Can we imagine a world in which there is transparent iron? Not unless our imaginings take place at a level of structural detail comparable to that of the imaginings of condensed-matter physicists who are trying to explain, say, the phenomenon of superconductivity. (1998: 79)

As the last sentence indicates, Van Inwagen sets the bar for genuine imagining extremely high. We do not imagine something unless we also imagine all the details — perhaps all the as-yet-undiscovered scientific detail — of how is it the case. If we were to imagine something at this level of detail, we would have evidence that it is possible. But there are very few things we can imagine at this level of detail, which means, according to Van Inwagen, there are very few things we can imagine. So there are very few non-actual modal propositions we are justified in believing. This is also the strategy of some die-hard materialists, who claim not to be able to imagine zombie cases because they are unable to imagine every last detail of a molecule-for-molecule duplicate. These bold claims seem to me far too strong. Presumably authors and artists use their imaginations to dream up all manner of strange and wonderful things. Certainly they don’t feel possibility as a constraint on their imagination. Is it not obvious that to imagine a world where wizards cast magical spells, we do not need to imagine how magic works? Someone reading a novel may succeed in imagining a man turning into a large cockroach though she lacks a degree in genetics. We stipulate that these things happen. We just don’t need to take such exclusively assignmentsupported imaginings as evidence for possibility.

V. Imagining Zombies In this final section, I would like to apply the theory developed thus far to an argument for dualism. In light of the repeated remarks about imagination’s power, even committed materialists should admit that they do imagine zombie cases; to deny

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that they do smacks of desperation. 22 If I am right, these materialists confuse what it takes to imagine something with a very high standard of what it takes for an imagining to be evidence for possibility. What they question is whether such imaginings provide any support for dualism. The difficulty for materialists is that, in the absence of considerations to defeat the evidential value of the imagining, a brute denial that the imagining provides modal evidence looks either too sweeping (if it amounts to skepticism) or completely ad hoc (if it is restricted to the imagining of zombies). Let us see how our considerations about assignments bear on the matter. The zombie case is the crucial step in one prominent argument for dualism. 23 The dualist appeals to the imaginability of zombies — physical duplicates of ourselves that lack conscious experience — to establish the possibility of zombies. If successful, it follows that the mental facts do not supervene on the physical facts. Materialism is refuted, and some form of dualism must be true. What is it to imagine one’s zombie twin? Here is what I do: I picture in my mind’s eye someone (something?) who looks exactly like me. Let’s call him (it?) Dieter. I imagine this creature, Dieter, typing on a computer on a muggy afternoon. Every now and again, Dieter takes a swig of coffee. It is part of my imagining that Dieter is not phenomenally conscious. There is nothing it is like to be Dieter; it is “all dark inside” for him/it. This last phrase “all dark inside” suggests to some authors that imagining one’s zombie twin requires imagining being a zombie, imagining it sympathetically, from the first-person point of view, or from the inside. Thomas Nagel in a footnote of “What Is It Like to Be a Bat?” offers a tentative diagnosis of the problem with zombie imaginings: imagining a zombie requires an illegitimate combination of first-person and thirdperson (perceptual, from the outside) imagining. Several authors, including Christopher Hill and Nagel himself, have developed this strategy into a defense of materialism against the zombie argument. 24 These defenses appeal to a general rule, that whenever our imagining contains someone who is conscious, has experiences of a certain kind, or indeed has other mental states, we employ the sympathetic imagination. This strikes me as a mistake, both as a general rule, and in the zombie case in particular. In reading a novel and imagining various characters interacting, I imagine evil Count Olaf ecstatic and anticipating the Baudelaire fortune, Klaus frightened, and Violet hatching a plan to thwart Olaf; I may picture all three characters in my mind’s eye, “from the outside.” I do not, in my imagining, pop “inside” each person’s head to establish that they are conscious creatures, or that they have the emotions or thoughts I imagine them to have. This is typically how it is 22

I think that most materialists can imagine their zombie duplicate. However, I do allow that, as a psychological fact, some may not be able to. What I deny is that nobody can imagine their zombie duplicate. 23

There are many versions of this argument, and Kripke’s revival of it (1972) has sparked great interest in recent literature. See, e.g., Chalmers 1996, Bealer 1994, Jackson 1994. 24

The original bat paper is Nagel 1974; see footnote 11, 526–27. See also Hill 1997 and Nagel 2002: §V (“What’s wrong with the conceivability argument”). Nagel 1974 and Hill both use the term “sympathetic imagination.”

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with imagining, I take it. In our imaginings (even our first-person imaginings) we encounter other people and creatures with mental lives, and do not have to adopt their point of view to give them mental lives in our imagining. This is all done with assignments. 25 Suppose we do what we typically do with a zombie case. Imagine your zombie twin “from the outside.” You picture in your mind’s eye something that resembles you a great deal, and perhaps looks to be doing exactly what you are doing at this moment. To make this a true zombie case requires two assignments: (i) that this creature is a microphysical duplicate of you; and (ii) that this creature has no conscious experience (for ease of exposition, let us suppose the assignments in question are stipulations; the point will go through if either or both are labels). Imagining a situation without both (i) and (ii) is not yet to imagine a zombie case. If, e.g., you imagine someone who looks just like you and is merely stipulated to have no conscious experience, you have not yet imagined a zombie case, because your imagining is consistent with your imagined twin being microphysically dissimilar. Clearly this case violates the negative thesis we have been developing: in imagining a situation of which it is intuitive that one has a zombie twin, the target proposition follows from the stipulations alone, and hence provides no evidence for the possibility of zombies. Let me be clear about what I am claiming. I said that we do not have to imagine zombie cases “from the inside.” When we imagine zombie cases from the third person, they provide no evidence for possibility. I have left open whether we can also imagine zombie cases from the inside. As a matter of fact, I do not think so, but exploring this issue would require a detailed analysis of first-person imaginings. We would also need such an analysis to analyze Descartes’s analogue of the zombie case, imagining oneself as a disembodied soul. I will have to leave that analysis for another occasion. I close with a few brief remarks about non-sensory imagination. Frequently in discussions of conceivability, philosophers introduce sensory imagination, make some claims about its probative value as modal evidence, and then simply assert that there is a non-sensory imagination that is equally evidentially valuable. For instance, Yablo writes in a footnote: Some philosophers use “imagine” so that imagining a thing is imaging it, that is, conjuring up an appropriate sensory presentation. I do not require a sensory-like image for imagining, and certainly not a distinct such image for distinct imagining. (1993: 27n55)

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Shoemaker argues (1993: 506) that we cannot imagine zombies “from the third-person perspective” because in imagining our zombie from the outside there is no “data gathering” that we can do — in our imagining, we have to suppose — that would entitle us to say that they are not conscious. But much of the goings-on in imaginings are assigned, even in imaginings from the outside. We do not need to do “data gathering” if the issue in question is settled by assignment.

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In the discussion of imagination that follows, all of Yablo’s examples employ what he would call “imagistic” imagining. There are no examples of probative non-sensory imaginings. Chalmers attempts to say more: There is a sense in which we can imagine situations that do not seem to be potential contents of perceptual experiences. One can imagine situations beyond the scale of perception: for example, molecules of H2O, or Germany winning the Second World War. One can imagine situations that are unperceivable in principle: for example, the existence of an invisible being that leaves no trace on perception.… In these cases, we do not form a perceptual image that represents S. Nevertheless, we do more than merely suppose that S, or entertain the hypothesis that S. Our relation to S has a mediated objectual character that is analogous to that found in the case of perceptual imaginability. In this case, we have an intuition of (or as of) a world in which S, or at least of (or as of) a situation in which S, where a situation is (roughly) a configuration of objects and properties within a world. We might say that in these cases, one can modally imagine that P. One modally imagines that P if one modally imagines a world that verifies P, or a situation that verifies P. Modal imagination goes beyond perceptual imagination, for the reasons above, but it shares with perceptual imagination its mediated objectual character. (Chalmers 2002: 151)

The position I am inclined to accept is the one Chalmers specifically rejects, that nonsensory imagining amounts to nothing more than supposition. But I need not argue for this stronger position. In my view, an imagining that lacks an image will have only assigned content that does not derive from the image — it will have only stipulative content. All the arguments in §IV against the probative value of purely assigned content still apply: we have reasons not to take pure stipulation as modal evidence. It is interesting to compare Kripke’s remarks (1972) on the subject of conceivings, for there he cautions that “possible worlds need not be given purely qualitatively, as if we were looking through a telescope” (50). “Generally, things aren't found out about a counterfactual situation, they are stipulated” (51). This is true, some of the content of an imagining is assigned, as I have acknowledged. But I claim that these assignments had better not, by themselves, establish the truth of the proposition conceived.

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Unger, P. (1975). Ignorance: A case for scepticism. Oxford: Clarendon Press. Van Cleve, J. (1983). Conceivability and the Cartesian argument for dualism. Pacific Philosophical Quarterly, 64, 34–45. Van Inwagen, P. (1998). Modal Epistemology. Philosophical Studies, 92, 67–84. Wittgenstein, L. (1965). The blue and brown books. New York: Harper & Row. (Original work published 1958) Yablo, S. (1990). The real distinction between mind and body. Canadian Journal of Philosophy supplementary volume 16, 149–201. Yablo, S. (1993). Is conceivability a good guide to possibility? Philosophy and Phenomenological Research, 53(1), 1–42. Yablo, S. (2000). Textbook Kripkeanism and the open texture of concepts. Pacific Philosophical Quarterly, 81[1], 98–122.

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