Idealism and Illusions Robert Smithson Forthcoming in the European Journal of Philosophy. Please cite published version. Abstract: According to the idealist, facts about phenomenal experience determine facts about the physical world. Any such view must account for illusions: cases where there is a discrepancy between the physical world and our experiences of it. In this paper, I critique some recent idealist treatments of illusions before presenting my own preferred account. I then argue that, initial impressions notwithstanding, it is actually the realist who has difficulties in adequately accounting for the distinction between illusion and reality.1 1 Introduction Recently, there has been a renewed interest in idealist metaphysics.2 According to the idealist, facts about phenomenal experience determine facts about the physical world. Any such view must respond to the following objection: Discrepancy Objection: In many cases, we think that the physical world does not align with our experiences. The idealist cannot accommodate the discrepancies between the physical world and our experiences of it.3 In this paper, I will explain how the idealist should respond to this objection. After some brief background, section 3 will consider some responses to the Discrepancy Objection from the recent literature. I will present my own preferred response in section 4. To conclude the paper, I will argue that the idealist can turn the Discrepancy Objection on its head. Initial impressions notwithstanding, it is actually the realist who has difficulties in accounting for the distinction between illusion and reality. 2 Preliminaries I will provide a more precise characterization of idealism and the Discrepancy Objection in 2.2 and 2.3, respectively. But to see why we should even care about these issues, I will first review some reasons why philosophers have again become interested in idealism. 1 (i) The mind-body problem : The two most prominent responses to the mind-body problem are materialism and dualism. Here, materialism is the view that physical facts, but not phenomenal facts, are fundamental, while dualism is the view that physical and phenomenal facts are both fundamental. Materialism faces difficult challenges, such as the conceivability argument and the knowledge argument. But dualism faces its own challenges, such as the causal exclusion argument.4 To avoid this dilemma, some philosophers have argued that we should reject the above dichotomy and instead accept idealism.5 (ii) Considerations from physics: Pelczar (2015) claims that idealism is needed to explain how phenomenal experience is compatible with relativistic spacetime. According to relativity, there is no objective simultaneity relation between events at different points in spacetime. But in experience, it often seems as though qualia are instantiated objectively simultaneously. So Pelczar argues that consciousness cannot be located within physical spacetime. But then how are they related? Pelczar ultimately concludes that phenomenal facts must ground the physical facts. (iii) Intelligibility : Many philosophers have thought that physics cannot provide an account of the intrinsic nature of physical properties; at best, it provides as with a structural characterization of these items, describing how they relate to one another. By contrast, our grasp of experiential properties (i.e., qualia) seems more substantial. So philosophers have argued that idealism provides the only account of reality on which the intrinsic nature of the physical world is intelligible to us (see, e.g., Yetter-Chappell (2017, 3.2)). 2.1 An epistemic motivation There is one further epistemic motivation for idealism that is of particular relevance to the discussion ahead. According to standard realists, there could be worlds where all typical human experiences are just as they are, but where manifest truths are radically different than we take them to be. A classic example of such a possibility is an envatted brain scenario.6 Idealists have argued that, if such possibilities are indeed coherent, then our experiences are unable to justify our judgments about the physical world. But it is obvious that our experiences do justify many such judgments. So realism is false. By contrast: insofar as she countenances a close dependence between phenomenal and physical truths, the idealist denies (or at least may deny) the coherence of these alleged skeptical scenarios. So, it is argued, idealism can avoid the skeptical worries arising for realism. Of course, realists deny that their position leads to skepticism. More pointedly, most realists will resist the suggestion that rejecting (e.g.) envatted brains scenarios is an advantage for idealism. Indeed, the realist may argue that, given the obvious coherence of this type of global illusion, any form of idealism that rules out such possibilities must be mistaken. I will set this issue aside for now. This is because my purpose in this paper is not to criticize realism, but is instead to defend idealism from the Discrepancy Objection. 2 Suffice to say that many idealists want to claim a certain epistemic virtue for their view: that it deflates certain scenarios traditionally used to motivate skepticism about the external world.7 So in the discussion ahead, I will specifically consider whether the idealist can respond to the Discrepancy Objection in a way that is compatible with this (alleged) epistemic virtue.8 That being said, I think that the response to the Discrepancy Objection that I develop below can also be used to support the idealist's views on skeptical scenarios. So I return to consider the epistemological dispute between the realist and the idealist in 4.5. 2.2 Clarifying thesis I will use the label "manifest properties" to refer to the various physical properties that seem to be presented to us in experience: colors, shapes, distance relations, and so on. Correspondingly, I will refer to truths such as 'x is blue', 'x is circular', and 'x and y are twice as far apart as x and z' as manifest truths.9 I will characterize idealism as follows: Manifest Idealism: Manifest truths are determined by truths about actual and counterfactual10 phenomenal experiences. Many idealists want to defend the stronger claim that all physical truths are determined by phenomenal truths. But with the restriction to manifest truths, I can set aside certain complications that arise for other families of truths. For ease of presentation, I will shorten "manifest idealism" to "idealism" in the discussion ahead. According to idealism, phenomenal truths determine manifest truths. Here, I mean for the determination relation to imply that phenomenal truths are (in some sense) prior to manifest truths. Greco (2017) offers a similar characterization of idealism in terms of metaphysical grounding. I use the term 'determine' in a slightly more general sense to include views involving metaphysical dependence as well as views in which manifest truths are semantically determined by phenomenal truths (see Smithson (manuscript) for this type of view). This distinction can be safely ignored in the discussion ahead. 2.3 The Discrepancy Objection I will present the Discrepancy Objection itself. There are many cases where we think that the physical world is different from how we experience it. For example, suppose a stick is halfway submerged in water so that our visual experiences present the stick as crooked. Must the idealist say that sticks become crooked whenever they are submerged in water? We can express the general worry as follows: Discrepancy Objection: In many cases, we think that the physical world does not align with our experiences. The idealist cannot accommodate the discrepancies between the physical world and our experiences of it. So the idealist faces a challenge. In order to secure the alleged epistemic virtue discussed in 2.1, the idealist needs to draw a close connection between the physical world and our 3 experiences of it. But this connection cannot be too close, or else the idealist will fail to uphold the distinction between illusory and non-illusory experiences. Is it possible to account for this distinction without forfeiting the (alleged) epistemic virtue that many have found attractive about idealism? 2.4 Counterfactual experiences As a final preliminary note, I will comment on the appeal to "counterfactual experiences" in the formulation of idealism. There are many parts of the physical world that no conscious subject has ever experienced. To account for this fact, many idealists appeal to counterfactual experiences: the experiences that subjects would have if conditions were different.11 For this reason, I have appealed to counterfactual experiences when formulating idealism. "Counterfactual experiences" should be understood broadly to include all experiences subjects would ordinarily consider relevant to assessing manifest truths. For example, in the case of S ≡ 'There is a cup on the table', counterfactual experiences might include: the experiences we would have if we were to look towards the table, the experiences we would have if we were to attempt to lift the apparent cup, the experience we would have if we were to look into a mirror reflecting the table, the experience we would have if we were to use a drone to photograph the table, and so on.12 The appeal to counterfactual experiences raises several questions: -Given the idealist's assumption that there is no mind-independent physical world, what grounds the counterfactual experiences appealed to by the idealist?13 -How will the idealist account for manifest truths in environments where no conscious experiences are nomically possible (e.g., truths about the insides of stars)?14 -Can the idealist appeal to counterfactual experiences without falling into circularity or regress?15 These are important questions, but it is outside the scope of this paper to address them. For now, I will simply assume as a working hypothesis that the idealist can legitimately appeal to counterfactual experiences. 3 Possible solutions In this section, I will consider some possible responses to the Discrepancy Objection. I will present my own preferred response in section 4. 3.1 Appeal to intrinsic differences in phenomenal character On the first proposal, illusory and non-illusory experiences are distinguished on the basis of intrinsic differences in their phenomenal character (that is: what it is qualitatively 4 like for a subject to have such experiences). Consider the following passage from Austin (1962, 49-50): Again, it is simply not true to say that seeing a bright green after-image against a white wall is exactly like seeing a bright green patch actually on the wall; or that seeing a white wall through blue spectacles is exactly like seeing a blue wall; or that seeing pink rats in D.T.s is exactly like really seeing pink rats; or (once again) that seeing a stick refracted in water is exactly like seeing a bent stick. In all these cases we may say the same things ('It looks blue', 'It looks bent', etc.), but this is no reason at all for denying the obvious fact that the 'experiences' are different. If the suggestion here is correct, the idealist can give a simple response to the Discrepancy Objection: an experience E is non-illusory iff it has certain characteristic types of intrinsic phenomenal character. This proposal seems plausible in many contexts; for example, there are plausibly differences in intrinsic phenomenal character between dreams and non-dreams. Nonetheless, there is a familiar argument for thinking that it is at least possible-even scientifically possible-for there to be illusory experiences which have the same phenomenal character as non-illusory ones. In ordinary cases, our phenomenal experience depends on certain distal causes in our surrounding environment. But these distal causes generate phenomenal experience only via a series of more immediate links in a causal chain (e.g., retinal stimulations, stimulations of the sensory and motor transducers of the central nervous system, etc.). It seems that one's phenomenal experiences would be the same even if the causes of the stimulations of one's central nervous system were different from what they actually are. The classic example is an envatted brain: if a scientist delivered appropriate signals to your envatted brain, it seems plausible that your experiences could have the same phenomenal character as non-illusory experiences.16 If this argument is correct, the current proposal does not provide the idealist with an adequate account of the distinction between illusory and non-illusory experiences. 3.2 Appeal to a reality independent of human mentality As formulated in 2.2, idealism is the view that manifest truths are determined by truths about actual and counterfactual phenomenal experiences. But it is consistent with this thesis to claim that manifest truths are independent of human phenomenal experiences in particular. Any such idealist can respond to the Discrepancy Objection by adopting the same general account of illusion as the realist: an experience E is non-illusory iff it aligns (in some sense) with an external reality that is independent of human mentality. As a representative example of this strategy, I will consider a view developed by YetterChappell (2017), which I will call the unity of consciousness view. Yetter-Chappell defends a form of idealism on which physical reality is constituted by a complex phenomenal unity governed by laws of nature: 5 External reality is a vast unity of consciousness, independent from all finite minds. This unity is vastly more complex than the unities we're directly acquainted with. Consider my cup. The cup exists independently of any (finite) minds insofar as it is a part of this vast phenomenal unity. But what's included in the phenomenal unity isn't merely the sensations I have when perceiving the cup from a particular vantage point. The unity must include the experience of the cup from every possible perspective it could be viewed from, binding together the experience of the cup from every possible angle and also from every possible sort of perceiver (humans, bugs, bats, color-inverts, etc.) (68) With this metaphysical picture as background, Yetter-Chappell offers the following account of perception: In perception, the objects of perception (or at least the perceived facets of these objects) are literally a part of my mind. When I perceive the world around me, my mind overlaps with---and is partially constituted by---bits of the phenomenal tapestry that is reality. Consider the blue cup, sitting on my desk. The cup is a bundle of sensory impressions: blueness-fromhere, cylindricalness-from-there, and so on. ... What it is for me to perceive the blueness of the cup is for that aspect of reality (that "thread" of the phenomenal unity) to literally be a part of my mind. (71) In order to account for illusory experiences, Yetter-Chappell clarifies that not all threads of our phenomenal experience are part of the unity of consciousness that constitutes reality: Were I to hallucinate a bloody dagger in front of my computer screen, the threads of my total phenomenal experience corresponding to computer would also be elements of reality, whereas the bits of phenomenology corresponding to the (apparent) bloody dagger would be bound up in my unity of consciousness, but not the phenomenal unity that is reality. ... So what distinguishes hallucination from perception is not the phenomenal character of the experience or the intrinsic metaphysical nature of the experience, but whether the experience involves a direct connection with reality. (72-73) While I think this view is intriguing, I will now raise a potential shortcoming with the proposal: that it forfeits the (alleged) epistemic virtue of idealism discussed in 2.1.17 According to realism, there is an external reality independent of the experiences of conscious subjects. The possibility of illusions shows that human experiences sometimes fail to align with this external reality. But then it also seems possible that all human experiences fail to align with this external reality (as in, e.g., an envatted brain scenario). So realism confronts the worry of external world skepticism (see 2.1). But the epistemic situation with Yetter-Chappell's view is very similar. The unity of consciousness view diverges from realism in allowing that external reality is constituted 6 by different phenomenal experiences. But in order to allow for illusory experiences, the proponent of this view acknowledges that external phenomenal reality may fail to include a given human phenomenal experience E. But then, it seems equally possible that external phenomenal reality might fail to include all typical human experiences. So, just as with realism, the unity of consciousness view seems to allow for the possibility of external world skepticism. This worry might be avoided if the unity of consciousness view offered an independent account of when human experiences contribute to external phenomenal reality.18 Indeed, I think that the proposal I offer in section 4 could fill exactly this type of role. My purpose in the present section has only been to show that merely appealing to an external phenomenal reality to resolve the Discrepancy Objection will not secure the (alleged) epistemic virtue of idealism discussed in 2.1. 3.3 Appeal to coherence Pelczar (2015) defends a version of phenomenalism according to which physical facts reduce to broadly phenomenological facts about (the coherence of) potential conscious experiences. For an intuitive grip on the view, consider the fact that Calcutta exists on the banks of the Hoogly River. Very roughly, Pelczar claims that this fact reduces to the fact that: if one were to have experiences as of standing by the side of a river with such-and-such features and facing in a certain direction, one would have experiences as of a city with so-and-so features---where such-and-such features are those that we think of as characterizing the Hoogly, and so and so features are those that we think of as characterizing Calcutta (143)19 In order to respond to the Discrepancy Objection, Pelczar offers the following analysis of deceptive appearances: An appearance of a physical object or event x is a deceptive appearance if and only if (1) it is an experience as of x, and (2) it is not best interpreted as a perception of x in the phenomenological limit (167) To illustrate the notion of the "phenomenological limit," consider the well-known MüllerLyer illusion. In isolation from any other actual or counterfactual experiences, your experience E of the Müller-Lyer figure is best interpreted as a perception of lines of different length. But now consider E together with other experiences: the experience you would have if you measured the two lines with a ruler, the visual experience you would have if you occluded the arrow portions of the figure, etc. Collectively, these experiences (together with all other counterfactually-supported experiences) are best interpreted as presenting a world where the lines are of equal length and E is a deceptive appearance. I think that Pelczar provides a strong response to the Discrepancy Objection; indeed, the proposal I defend in section 4 has certain similarities with this account. But in this section, I will outline what I consider to be two shortcomings with Pelczar's proposal. 7 A first worry is that Pelczar's analysis of deceptive appearances still allows for the possibility of external world skepticism. Consider Pelczar's discussion of an envatted brain case: Is the [vat scenario] interpretable as including perceptions of trees, lakes, etc.? The most natural thing to say is that it is not. If we focus on the potential [experiences] associated with the envatted brains, [these experiences will] indeed evoke trees, lakes, and the rest. ... [But] when we take into account all of the potential experiences [including the experiences of subjects outside the vat] that characterize the vat scenario, we find that the experiences we previously interpreted as perceptions of trees and lakes are actually not best interpreted as perceptions of trees and lakes, but rather as perceptions of computational processes. (162) As seen in this passage, Pelczar's phenomenalist accepts that there can be cases where all of our experiences are just as we normally think, but manifest truths are radically different than we take them to be.20 So this type of idealist does not secure the (alleged) epistemic virtue discussed in 2.1.21 A second worry concerns the notion of a "best interpretation" of experiences. How a subject interprets experiences will depend on that subject's environment, cognitive makeup, and other dispositions. And these factors will vary from possible subject to possible subject. For example, consider the experience of what we would consider to be a white cube in a room full of red lights. In this case, humans would interpret the cube's pink appearance as deceptive. But now consider a community of aliens whose home world is everywhere diffused by reddish light. These aliens, we can imagine, would interpret the experience of the pink cube as non-illusory. This simple example shows that there can be different (and conflicting) ways in which a set S of experiences might be interpreted. So without further argument, there is no reason to think that there is some objectively best way to interpret S. But without an objectively best interpretation, it does not seem that the current proposal can provide the idealist with a response to the Discrepancy Objection. 4 Deference to ordinary epistemology I will now offer my own preferred response to the Discrepancy Objection. The basic strategy is to claim that the distinction between illusory and non-illusory experiences is internal to our ordinary epistemic practices and so is equally available to the idealist as to the realist. In everyday life, people know how to distinguish illusions from non-illusions, dreams from non-dreams, and so on. And they are able to draw these distinctions on the basis of the ordinary types of experiential evidence available to them. Even if they are unable to make a judgment about whether an experience is illusory on the basis of their actual experiential evidence, subjects recognize how further counterfactual experiences would 8 bear on such judgments. In this sense, the ability to distinguish between illusory and non-illusory experiences is a part of our ordinary epistemic practices. But if subjects in everyday life can distinguish non-illusory from illusory experiences on the basis of their ordinary experiences, the idealist can equally well draw such a distinction. This is because, whatever criteria ordinary subjects use to distinguish nonillusory experiences, the idealist can appeal to the exact same criteria. This is to say: whatever ordinary subjects treat as evidence for the accuracy of an experience E, the idealist can treat as (partially) determining the accuracy of E.22 4.1 The Deference Principle So what are the criteria that ordinary subjects use to distinguish illusory experiences from non-illusory ones? In fact, I think it would be a mistake for the idealist to try to offer an explicit analysis of these standards. Because the ordinary criteria for distinguishing non-illusory and illusory experiences are very complex, there is no reason to expect that any concise, informative set of necessary and sufficient conditions will fully capture them. Instead, the idealist should simply defer to how ordinary subjects themselves draw the distinction by endorsing the following principle: Deference Principle: Let Si be a manifest judgment. Let si be the set of (ordinary) experiences human subjects would (ideally) consider relevant to assessing the truth of Si. Then a (counterfactual) experience e contributes to determining the truth of Si just in case e is a member of si. In particular, Si is true just in case human subjects would (ideally) judge that Si is true when presented with all of the experiences in si. To provide an intuitive grip on the principle, consider the following example: Case 1: S1 ≡ The opposite side of this book is blue. Which experiences do human subjects ordinarily consider relevant to assessing the truth of S1? One set are the visual experiences I would have if I were to rotate or flip the book around. Another set are the experiences I would have if I were to walk around to the other side of the book, looking at it from the opposite direction. Another set are the experiences other subjects would have when looking at the book from the opposite direction. Another set are the experiences I would have if I were looking into a mirror placed behind the book. All of these experiences will be members of s1. And this merely scratches the surface: any competent subject can imagine (and recognize) countless other examples. The Deference Principle describes how all of the experiences just described determine the truth of S1. In particular, the Deference Principle stipulates that S1 is true just in case ordinary subjects presented with all of the above experiences would judge that S1 is true.23 9 4.2 Clarificatory notes Here are a few clarificatory notes on the Deference Principle.24 (i) Contextualized experiences: The experiences relevant to the principle must be contextualized-that is, presented to a subject with a description of what types of experiences they are. Each experience in si should be paired with a description that includes (at minimum): (a) the subject in question and (b) a description of the counterfactual situation relevant to the experience. Without this information, a subject would be unable to interpret how the experiences in si bear on the truth of Si. (ii) The Cosmoscope: There are various ways to explicate the idea of a subject being "presented with the experiences in si". One option is to invoke Chalmers' (2012, 114-116) notion of a "Cosmoscope". The Cosmoscope is a hypothetical virtual reality device that allows a user to select a certain counterfactual experience and which then induces that experience in the user.25 For example, a user might select: the experience I would have if I were in position p at time t and were to look towards the book. After appropriate warning, the Cosmoscope would induce this experience in the user. We can think of the subjects in the Deference Principle as using a Cosmoscope to learn about all of the counterfactual experiences relevant to Si. (iii) Idealizations: The Deference Principle appeals to the experiences ordinary subjects "ideally" consider evidentially relevant to a given judgment Si. To see why this idealization is needed, consider S2 ≡ 'The bicycle is blue'. s2 cannot be viewed as the experiences considered relevant to S2 given our actual evidence; after all, our actual evidence may suggest that the bike is in the closet when, in fact, it is outside. Instead, s2 should include the experiences considered relevant to S2 after a certain process of idealized evidence-gathering. I describe how the idealist should understand this process in Smithson (manuscript b). These details can be safely ignored in the discussion ahead.26 (iv) Ordinary experiences: By "ordinary" experiences, I just mean: the kinds of experiences that we have in human life as it normally comes to us. This restriction is intended to rule out, e.g., the experience I would have if there was a God who told me the truth of P, the experience I would have if I had a faculty that allowed me to directly intuit the truth of P, the experience I would have if scientists controlling my envatted brain revealed their presence to me, and so on. (For now, I will take this restriction as given; I will explain why the Deference Principle appeals to this restriction in 4.5.) 4.3 Illusions and the Deference Principle Having provided a basic overview of the Deference Principle, I will now discuss how this principle can help the idealist respond to the Discrepancy Objection. Consider the following canonical example of an illusion: Case 3: S3 ≡ The stick is straight. (Assumption: The stick is partially submerged in water.) It is useful to think of S3 as a case where the experiences in si do not form a mutually coherent set. s3 will include many experiences that indicate that S3 is true: the tactile 10 experiences of the stick, the experiences of the stick when it is taken out of water, and so on. But s3 will also include many experiences that indicate that S3 is false, such as the visual experiences of the stick when it is halfway submerged in water. So what is the truth value of S3, given that s3 is not a mutually coherent set? The answer is built into the Deference Principle: S3 is true just in case ordinary human subjects would judge that S3 is true when presented with all of these experiences. In this case, subjects clearly would judge that the stick is straight. After all, we make this judgment on the basis of similar evidence in ordinary contexts all the time. So the idealist will say that S3 is true and that sticks partially submerged in water remain straight. Here is a second example: Case 4: S4 ≡ In Fig. 1, square B is a lighter shade than square A. Fig. 1: The Checker-Shadow Illusion27 Our visual experience of the left copy of the image suggests that S4 is true. But our visual experience of the right copy of the image-where grey columns have been added- suggests that A and B are the same color. Both of these experiences are members of s4 (along with countless other experiences). If presented with these experiences, ordinary subjects would judge that S4 is false. After all, this is the judgment we actually make when presented with the copies of the image in Fig. 1. So the idealist will say that the squares in the figure are the same shade. "But what if the experiences that suggest that S4 is false turn out to be misleading as well?" Then there will be further experiences within s4 that reveal this to be the case; this is because s4 is stipulated to include all experiences that human subjects would consider relevant to the truth of S4. 28 Here is a third example: Case 5: S5 ≡ There is a tiger in the kitchen. Suppose that one's occurrent visual experience E1 is of a tiger in the kitchen. Does this mean that S5 is true? Or is the experience instead a hallucination? With just this information, we cannot yet say; this is because the truth of S5 is determined by the set of all ordinary experiences human subjects consider relevant to assessing its truth. For example, s5 will include the visual experiences of other subjects in the kitchen. If (as is most likely) these experiences fail to present a tiger, this would (typically) suggest that S5 is false (and that E1 is a hallucination). 11 4.4 External world skepticism? How will the Deference Principle treat the scenarios traditionally used to motivate skepticism about the external world (see 2.1)? Consider the following envatted brain case: Case 6: S6 ≡ There is a cup on the table. Assumption: We are in an envatted brain scenario, having experiences of a cup on a table. For the purposes of this example, it does not matter what particular idealist metaphysics we adopt to make sense of the assumption in case 6. For example, we might suppose that there is some phenomenal unity independent of human mentality (see 3.2), and this phenomenal reality is a world that includes envatted brains. Or we might suppose that there are certain facts about potential phenomenal experiences that metaphysically ground a world with envatted brains (see 3.3). s6 will include: the experiences we would have if we were to look towards the table, the experiences we would have if we were to attempt to lift up the apparent cup, the experience we would have if we were to look into a mirror reflecting the table, the experience we would have if we were to use a drone to photograph the table, and so on. What about the experiences-call them external experiences-of the (possible) subjects who are outside of the vat? In contrast to previous proposals, the Deference Principle denies that these external experiences are relevant to determining the truth of S6. This is because the experiences in s6 are restricted to ordinary experiences (see 4.2). (I will discuss further explain and justify this restriction in 4.5.) Subjects presented with the various ordinary experiences in s6 clearly would judge that S6 is true; after, we make these kinds of judgments about the physical objects in our environment all the time. Similar remarks apply to other scenarios-e.g., evil demon cases, simulation cases-that are used to motivate skepticism about the external world. As standardly conceived, these are cases in which no ordinary experiences reveal the "underlying reality" giving rise to our phenomenal experiences. So these will be cases where (according to the Deference Princple) our (typical) judgments about the physical world are true. By deflating these types of skeptical scenarios, the idealist endorsing the Deference Principle secures the epistemic virtue discussed in 2.1.29 (N.b.: I use the term "deflates" because the Deference Principle does not rule out the epistemic possibility that we are (in some "underlying reality") envatted brains. Instead, it establishes that our typical beliefs about the physical world are still true even in such a scenario, thereby deflating the case's alleged skeptical import.30) 4.5 Turning the objection I have claimed that deflating alleged skeptical scenarios (like the envatted brain scenario) is an epistemic virtue for the idealist. But many philosophers will disagree with the Deference Principle's verdict about S6. They will claim that, in such a scenario, S6 is manifestly false.31 In this section, I will explain why I think that the rejection of 12 this type of illusion is indeed an virtue of idealism. This will, in turn, help justify the restriction to ordinary experiences in the Deference Principle (see 4.2). Suppose it turns out that, in fact, we are in an envatted brain scenario. Suppose further that we come to learn this somehow (perhaps we look through a powerful telescope and see the message "You are an envatted brain" written in English in the distant stars). Upon learning this result, we might initially react by saying things like: "Everything we see is merely an illusion!" and "None of our experiences accurately represent the world!" But this shock would pass. And after several minutes, we would return classifying experiences as illusory or non-illusory just as we did before. We would, for example, return to saying things like: 'The stick's appearance is deceptive; it is actually straight' and 'The figure on the left is real, while the figure on the right is just an illusion'. This is unusual. Usually when we receive evidence E that contravenes our judgment that P , we abandon our judgment that P . But in the above thought experiment, we would return to making our original judgments about which experiences are illusory even after receiving evidence that-by the realist's lights-shows that all of our experiences are illusory. There are various ways the realist might account for this behavior. For example, she might claim that, after using the powerful telescope, we would change the meanings of the term 'illusory' and 'non-illusory'. Or she might claim that, after using the telescope, we would start to engage in a fiction on which some of our experiences are non-illusory. I raise objections to these and other proposals in Smithson (2017). By contrast, the idealist will interpret the above thought experiment as showing that the realist is simply mistaken in supposing that the distinction between illusory and non-illusory experiences ultimately hinge on facts about some external reality that is completely independent of human experience. The thought experiment reminds us that, in fact, this is a distinction that subjects are (in principle) able to make on the basis of the types of experiential evidence that are ordinarily available to them. As the terms 'illusory' and 'real' are actually used in everyday life, they are meant to mark the distinction between (e.g.) our experiences of partially submerged sticks and (e.g.) our experiences of those sticks once they have been removed. This should not be surprising; a distinction on which every experience counts as illusory would be completely useless to us.32 This thought experiment helps illustrate the fundamental reason for the restriction to ordinary experiences in the Deference Principle: it is so that idealism is in alignment with the ordinary epistemology of our judgments about the physical world. By ruling out envatted brain scenarios, the Deference Principle allows the idealist to respect the distinction between illusion and reality as it is actually drawn by human subjects. By contrast, because it claims that the accuracy of an experience hinges on facts about some external reality (to which we may not have direct epistemic access), realism conflicts with the ordinary epistemology of our judgments about the physical world. The above discussion shows that the idealist can turn the Discrepancy Objection on its head. By rejecting the possibility that we are always suffering an illusion or always dreaming, the idealist respects the distinction between illusory and non-illusory 13 experiences as it is actually drawn by human subjects. By contrast, because she claims that the accuracy of an experience hinges on facts about some external reality to which we may not have direct epistemic access, the realist fails to draw this distinction in the correct way. Stepping back: one might wonder why it is important for a philosophical theory of illusions to align with our ordinary epistemic practices. Indeed, certain realists (and certain idealists as well) may claim that, in fact, it is inappropriate to look to ordinary epistemology in this way. In response: the thought that we can simply ignore ordinary epistemology when giving a theory of illusions is too simplistic. On any plausible metasemantics, our everyday use of illusion/reality distinction constrains what could deserve the label 'illusion'. If a theory T is incompatible with this use, T is simply failing to talk about illusions (the things we typically try to avoid in everyday life). Any philosopher defending it would simply be changing the subject. (Compare to Schaffer's (2004) analogous response to philosophers who would disregard the use of the term 'cause' when offering a theory of causation. Schaffer imagines a philosopher who claims: "The nature of causation is being over a mile apart, and no mere human ... concepts can affect this" (207). It is clear that, whatever else we might say about it, this theory does not deserve to be called a theory of causation. This is because the theory has nothing to do with how the term 'cause' is actually used.) This is a difficult metaphilosophical issue that warrants further discussion. But at the very least, I hope to have explained why philosophers attracted to idealism for epistemic reasons (see 2.1) should endorse the restriction to ordinary experiences found in the Deference Principle . 4.6 Other types of global illusions In 4.4, I discussed the envatted brain scenario. What about other alleged types of indetectable illusions? In general, I think that two conditions must be met in order for the Deference Principle to deflate an alleged global illusion. First: the Deference Principle only deflates illusions that are indetectable in principle. This is because any (ordinary) experiences that would allow subjects to detect a given illusion will already be included in si (see 4.3 for discussion). For example, suppose that neuroscientists in the hospitals somehow wirelessly manipulate our brains so as to make all of our brown experiences appear lighter, so that some browns appear yellow.33 The Deference Principle will presumably not rule out this type of global color illusion, due to the fact that experiences "detecting" this illusion will be included in si. (For example, si might include (counterfactual) experiences as of scientists inserting chips into the brains in question, or of operating the controls, etc.). While perhaps initially disappointing, this is in fact what the idealist should say about the global color illusion case. To respect the ordinary distinction between illusions and non-illusions, the idealist should allow for illusions that are detectable in principle (even if, in fact, they are very difficult to detect).34 Second: the Deference Principle only deflates global illusions where the counterfactual experiences relevant to the Deference Principle are determinately supported. For 14 example, consider a temporal skeptical scenario to the effect that the world was created five seconds ago (and we merely have memories as of it extending farther back).35 Here, we suppose that there are no truths about, e.g., what a given subject would experience six seconds ago, ten years ago, etc. In this scenario, the phenomenal truths are simply too impoverished for the Deference Principle to determine a set of physical truths as obtaining in the past. For an even more radical case, suppose that somehow there are not any determinate facts about counterfactual experiences. For example: suppose that an evil demon causes all of our actual experiences, but that somehow the demon does not also ground any counterfactual experiences of any sort. In this extreme scenario, I doubt that any of our beliefs about the physical world will turn out to be true (according to the Deference Principle). Similar remarks apply to the scenario Chalmers (2006) calls the "chaos hypothesis," in which our experiences are simply randomly caused moment by moment and it is a miracle that they happen to exhibit the order and coherence that they do. These examples show that the Deference Principle cannot, by itself, deflate every type of global illusion (even when we are restricting attention to illusions that are in principle indetectable). The Deference Principle is able to deflate many traditional forms of "external world skepticism." But to deflate scenarios like the chaos hypothesis, the idealist will have to look elsewhere. On the other hand, we may temper any disappointment by observing that there is a major difference in intuitive plausibility between the chaos hypothesis and the envatted brain scenario. The former is difficult to take seriously at all: it seems miraculous to suppose that all of our experiences just "happen" to cohere in such an orderly way. By contrast, it is much more difficult to provide (non-question begging) reasons for thinking that the envatted brain scenario is similarly improbable. Unlike the chaos hypothesis, the envatted brain scenario does not leave our coherent experiences completely unexplained; for this reason, it has a much higher degree of initial plausibility. Similar remarks may apply (perhaps less convincingly) to the other scenarios mentioned above. For example, it is difficult to conceive how an evil demon could be causing our coherent and stable experiences if the demon's mind did not also ground counterfactual facts about what experiences subjects would have under different conditions. As for the hypothesis that the world was recently created: it posits enormously complex initial conditions. Perhaps this is explanatorily inferior to the hypothesis that the world had comparatively simple initial conditions, or the hypothesis that the world had no beginning at all. It is outside the scope of this paper to discuss these other types of skepticism in any detail. Suffice to say that the Deference Principle deflates skeptical scenarios meeting the above two constraints. This is advantageous insofar as these types of scenarios (e.g., envatted brain scenarios) are often very difficult to challenge without begging the question against the skeptic. 15 5 Conclusion: idealism and ordinary epistemology I have argued that the idealist can respond to the Discrepancy Objection by appealing to our ordinary epistemic practices. The fact that ordinary subjects are able to distinguish illusory from non-illusory experiences guarantees that the idealist can also draw such a distinction. To capture this strategy, our ordinary epistemic practices are directly built into the Deference Principle. This link to ordinary epistemology is important for a second reason. In 2.1, I raised the question: is it possible for idealism to account for the distinction between illusion and reality without forfeiting the epistemic virtue that has attracted many philosophers to idealism? We can now give a clear affirmative answer. Far from forfeiting the epistemic advantages of idealism, the idealist's response to the Discrepancy Objection reinforces these advantages. This is because ordinary epistemic practices are built into the Deference Principle. In fact, I have argued that the idealist can turn the Discrepancy Objection on its head, directing it back towards the realist. Insofar as the she claims that the accuracy of an experience depends on some external reality that is completely independent of human mentality, the realist fails to draw the distinction between illusions and non-illusions in the ordinary way. Notes 1 I would like to thank two anonymous referees for helpful comments on this manuscript. 2See, e.g., Adams (2007), Chalmers (2019), Foster (2008), Pelczar (2015, 2019), Segal & Goldschmidt (2017), Smithson (2017), Yetter-Chappell (2017), . 3Pelczar (2015, 9.3) calls this "the problem of deceptive appearances." 4See Chalmers (2010) for detailed discussion of these three arguments. 5For discussion, see, e.g., Chalmers (2019). See also Pelczar (2018), who defends phenomenalism on the grounds that it preserves a monist ontology while avoiding problems with materialism and other forms of idealism. 6There are certain realists who deny the coherence of envatted brain scenarios. But most realists view this as a skeptical possibility. 7For discussion, see Smithson (2017). 8As mentioned above, there are some philosophers who endorse idealism for non-epistemic reasons. These philosophers may not agree that preserving this epistemic virtue is a desideratum for solutions to the Discrepancy Objection. I hope that the discussion ahead will help convince the reader that this is an important desideratum after all. 9By contrast, the label "manifest truths" will exclude such truths as: 'x has a charge of 3e', 'x is a zebra', 'x is loved by John', and 'x has a palindromic name'. Some theorists, such as Siegel (2010), claim that "higher-level properties" (e.g., being a zebra) are also represented in experience. Whether or not this is correct, I will not count higher-level truths as manifest truths. 10 I clarify the notion of a "counterfactual experience" in 2.4. 11See, e.g., Berkeley (1713, 250-6), Dummett (2004), and Pelczar (2015). 12With the restriction to manifest truths (see 2.2), the terms 'cup' and 'table' in S should technically be replaced by more neutral expressions (e.g., 'cup-shaped object', 'table-shaped object'). This being said, I will continue to use terms like 'cup' as abbreviations in the discussion ahead. 16 13For relevant discussion, see Pelczar (2015, chs. 6-8). 14For discussion of this objection, see Pelczar (2015, 9.4). 15See Sellars (1963) for a version of this objection applying to early 20th-century versions of phenomenalism. 16See, e.g., Horgan & Tienson (2002, 526-527) for a version of this argument. 17The objection below may not worry those (like Yetter-Chappell herself) attracted to the unity of consciousness view for non-epistemic reasons. But hopefully, the discussion in 4.5 will convince such philosophers that the epistemic virtue discussed in 2.1 is important after all. 18At one point, Yetter-Chappell (2017, section 2) suggests that relations of coherence might be used to distinguish illusory from non-illusory experiences. I discuss this proposal in the next sub-section. 19This is a rough first pass; Pelczar offers a series of precisifications in order to respond to a variety of objections to this analysis. These details will not be relevant to the discussion ahead. 20It should be said: Pelczar (2015, 164-165) views his phenomenalism as compatible with the claim that we are not radically mistaken in (e.g.) an envatted brain scenario (although Pelczar himself thinks that we are mistaken in such a scenario). I agree with Pelczar about this compatibility, and I think that the proposal offered in section 4 could be combined with Pelczar's metaphysical view. 21The objection discussed below will not worry those (like Pelczar himself) attracted to phenomenalism for non-epistemic reasons. But hopefully, the discussion in 4.5 will convince such philosophers that the epistemic considerations in favor of idealism are important as well. 22This strategy is inspired by Berkeley's own response to the Discrepancy Objection; see Berkeley (1713, 235). 23There are a few types of experiences that, for ease of presentation, I will not mention in this or subsequent examples. These include: experiences of memories, experiences involving testimony (either from people, or encyclopedias, or other sources), and experiences that are only relevant to Si insofar as they support an inductive generalization that subsumes Si. 24I discuss the Deference Principle in greater detail in Smithson (2017). 25In fact, the Cosmoscope described by Chalmers is more complex. But its additional features will not be relevant to this paper. 26The Deference Principle also requires an idealization for the judgment about Si that abstracts away from our contingent cognitive limitations. For an example of an idealization that would work in the current context, see Chalmers (2012, 63-71). 27Image copyright owned by Adelson (1995). Used with permission. 28What about illusions that are in principle impossible to detect? I consider this possibility in 4.4. 29What about other types of global skeptical scenarios? I discuss this issue in 4.6. 30I thank an anonymous referee for suggesting this clarification. 31 Of course, certain realists deny that envatted brain scenarios are cases where physical truths are radically different than we take them to be (see Putnam (1981) for discussion). Nonetheless, in Smithson (2017), I argue that even non-standard realists will accept the coherence of certain scenarios where our manifest judgments are radically mistaken due to the external world having some surprising underlying nature. So the discussion of this section should apply to most forms of realism. 32If idealism is true, what explains our initial inclination to view the envatted brain scenario as a case of global illusion? I think this initial reaction is explained by the fact that we-or those of us initially sympathetic to realism-have false theoretical beliefs about our manifest judgments. We initially retract these judgments because we assume that they purport to describe some external reality fully independent of human mentality. But we soon return to our original manner of speaking because this theoretical assumption is mistaken. 33I thank an anonymous referee for example. 34One might worry that the idealist has no grounds for treating the color illusion scenario differently than the envatted brain scenario. After all, an envatted brain could be taken from its vat and inserted into a human body. This suggests that the vat illusion is detectable in principle just like the global color illusion. (I thank an anonymous referee for this objection.) But there is a difference between the cases. In the color scenario, we suppose that the illusion is in principle detectable through ordinary experiences: the kinds of experiences we have when following our 17 everyday methods of learning about the world. By contrast, in the envatted brain scenario (as typically conceived), there is no way to detect the vats through these ordinary methods. Instead, detecting the vats requires an "intervention" from, e.g., the scientists looking after the vats, which is an intervention over which we have no control. (Of course, there may be variants of the envatted brain scenario that should be treated similarly to the color illusion case.) As for why the Deference Principle focuses on ordinary experiences: I defended this restriction with the Oracle thought experiment in 4.5. 35I thank an anonymous referee for asking about this example. References Robert Adams (2007). Idealism Vindicated. 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