Skeptical appeal: the source-content bias* John Turri john.turri@gmail.com Abstract: Radical skepticism is the view that we know nothing, or at least next to nothing. Nearly no one actually believes that skepticism is true. Yet it has re- mained a serious topic of discussion for millennia and it looms large in popular culture. What explains its persistent and widespread appeal? How does the skep- tic get us to doubt what we ordinarily take ourselves to know? I present evidence from two experiments that classic skeptical arguments gain potency from an in- teraction between two factors. First, people evaluate inferential belief more harshly than perceptual belief. Second, people evaluate inferential belief more harshly when its content is negative (i.e. that something is not the case) than when it's positive (i.e. that something is the case). It just so happens that potent skeptical arguments tend to focus our attention on negative inferential beliefs, and we are especially prone to doubt that such beliefs count as knowledge. That is, our cognitive evaluations are biased against this specific combination of source and content. The skeptic sows seeds of doubt by exploiting this feature of our psy- chology. 1. Introduction We face uncertainty all the time. Doubt and ignorance are unavoidable facts of life. But they are neither permanent nor irreparable. As much as doubt and igno- rance dot the landscape of our existence, so too does knowledge. Inquiry reme- dies ignorance and diminishes uncertainty: we pass, step by step, from ignorance to knowledge, from uncertainty to understanding. In this respect, modern science is a macrocosm of the cognitive path we each take through life. Our cognitive * This is the penultimate version of a paper to appear in Cognitive Science. Please cite the fi- nal, published version if possible. 1 Skeptical appeal: the source-content bias | 2 powers are fallible and limited, but no less impressive for all that. Skeptics notoriously disagree. Radical skepticism is the view that we know nothing, or at least next to nothing. Some forms of skepticism allow that we know facts about how things currently appear to us (e.g. "I seem to be in pain") or obvi- ous basic conceptual truths (e.g. "2 > 1"). But, in general, to be skeptical about a domain is to deny that we know that specific propositions in that domain are true. Many researchers assume that knowledge is a mental state (Premack & Woodruff, 1978; Pillow, 1989; Povinelli, Nelson & Boysen, 1990; Perner, Frith, Leslie & Leekam, 1989; Povinelli & deBlois, 1992; Flavell, 2000; Williamson, 2000; Hare, Call & Tomasello, 2001; Sprung, 2010). Accordingly, we can frame skepticism in terms of mental state ascription: to be skeptical about a domain is to deny all knowledge ascriptions regarding that domain. People might have be- liefs or convictions or hopes or intentions about the domain, but they don't have knowledge. Skepticism lives a life beyond Philosophy 101. Skepticism readily captures the public imagination and is a staple of popular culture. Gaming boards feed on it. For instance, the motto of the New York State Lottery is, "Hey, you never know" (http://nylottery.ny.gov/wps/portal). Hollywood grows rich on it. Witness the many successful films that put skeptical doubts front and center. Foremost among these are The Matrix (do you know that you're not in The Matrix?), Vanilla Sky (do you know that you're life is not just a dream?), The Truman Show (do you know that your life isn't just one big charade?), Bladerunner (do you know that this individual isn't a replicant?), Dark City and Memento (do you know that you're past is what it seems to be?). If nothing else, skillful trafficking in skeptical doubt is a lucrative business. Not only does skepticism live a life be- yond Philosophy 101, but apparently the skilled skeptic can live lavishly. Nevertheless, just as no battle plan survives contact with the enemy, radical skepticism doesn't survive contact with daily life. The skeptic tells us that we 3 | John Turri don't know that we're not merely dreaming, or that other people have minds, or that the universe is older than five minutes, or that our past is what it seems to be, or that there is an objective world outside our minds, or that snow is white, or that the next time we eat bread it will nourish us, etc. (Sextus Empiricus; Descartes, 1641; Bayle, 1702; Berkeley, 1710; Hume, 1748; Russell, 1921; Unger, 1975). We find these assertions incredible and are prone to reject them out of hand as ridiculous and inconsistent with common sense (Reid, 1764). Sane peo- ple do not and cannot seriously doubt such things in practice. But even granting that this is the wise response, residual dissatisfaction remains. Unless we're able to identify a flaw in the skeptic's performance - some error or trick that takes us in - thoughtful people will continue to find the situation somewhat troubling (Stroud, 1984; DeRose, 1995). True, we carry on with our lives in much the same way (Hume, 1739: Bk 1.4.7); but it is with a slightly heavier heart. No matter if we can't figure out how the peddler swindles people with his shell game, the wise person just walks right by and keeps her money in her pocket. But the curious wise person still feels the mild sting of ignorance and suffers more than a mod- icum of intellectual anxiety. All this raises an interesting psychological question. If nearly no one accepts skepticism, then why do skeptical arguments perennially fascinate us? Why do we, individually and collectively, over thousands of years, keep revisiting skepti- cism? This paper begins the task of explaining what in our psychology renders us vulnerable to these skeptical doubts. This entails a subtle shift in focus from the recent flurry of valuable experimental work on commonsense cognitive evalua- tions (Swain, Alexander & Weinberg, 2008; Wright, 2010; May et al., 2010; Beebe & Buckwalter, 2010; Feltz & Zarpentine, 2010; Starmans & Friedman, 2012; Schaffer & Knobe, 2012; Beebe & Jensen, 2012; Sripada & Stanley, 2012; Turri, 2013; Nagel, San Juan & Mar, 2013; Myers-Shulz & Schwitzgebel, 2013; Skeptical appeal: the source-content bias | 4 Murray, Sytsma & Livengood, in press; Buckwalter & Schaffer, in press; Buckwal- ter, Rose & Turri, in press), otherwise known as "folk epistemology" (Mont- gomery 1992; Bartsch 2002; Hardy-vallée & Dubreuil 2010; Mercier 2010; Spicer 2010; Turri & Friedman 2014). While knowledge attribution has been the focus of considerable attention recently, its conceptual flip-side has not: knowledge denial. Knowledge denial is the skeptic's stock in trade. So our guiding question might be put this way: how does the skeptic get us interested in purchasing his wares? 1.1. The classical argument for skepticism and two examples We will focus on the most celebrated and influential skeptical strategy (Descartes, 1641; Moore, 1959; Dretske, 1970; Unger, 1975; Stine, 1976; Goldman, 1976; Lewis, 1979; Nozick, 1981;Stroud, 1984; Cohen, 1988; DeRose, 1995; Sosa, 1999; Pritchard, 2002; Cohen, 2005; for an overview see Turri 2014, esp. §§1-4, 19-23, 47-49). The strategy is to proceed in three stages. First identify some claim that we would ordinarily take ourselves to know (call it 'O' for 'ordinary claim'). Next identify some tricky claim (call it 'T' for 'tricky claim'), the denial of which (~T) obviously follows from O. It's important that we have the intuition that we ordi- narily could not know ~T. Then reason as follows. 1. If we know that O, then we know that ~T. 2. But we don't know that ~T. 3. So we don't know that O. This is sometimes called "the classical argument for skepticism" and charac- terized as "exceedingly compelling" (Unger, 1975: 8–9). The argument is logically valid and appeals to premises that we find plausible. Yet its conclusion is incredi- ble and contradicts something we normally take for granted. Some consider this to be a genuine paradox (Cohen, 1988). For decades resolving this paradox has 5 | John Turri been a central concern in the theory of knowledge. This classic argumentative strategy can be used to challenge many, if not most, of the things we ordinarily take ourselves to know (Vogel, 1990; Hawthorne, 2004). We'll briefly consider two examples familiar from the litera- ture on skepticism, which will then inform the experimental studies reported be- low. First, we ordinarily take ourselves to know where various objects important to us are. For instance, when Maxwell is done at work for the day, he knows that his car is parked in the parking garage (O). However, it's not uncommon for cars to be stolen. Does Maxwell know that his car has not been stolen (~T)? It can eas- ily seem that Maxwell does not know this (Vogel, 1990). But, of course, Maxwell does know that if his car is parked in the garage, then it hasn't been stolen (if O, then ~T). So, the skeptic invites us to conclude, Maxwell doesn't know where his car is after all. Second, we ordinarily take ourselves to know what natural kinds things be- long to. For instance, if Zoe goes to the zoo and sees a large, menacing, spotted fe- line in the exhibit labelled "Jaguar," she knows that the animal is a jaguar (O). However, it's not unheard of for zoos to make mistakes or temporary substitu- tions in a pinch to please their patrons. Does Zoe know that the animal is not a leopard that looks just like a jaguar in a jaguar display (~T)? It can seem that Zoe does not know this (Dretske, 1970: 1016; Unger, 1975: 8). But, of course, Zoe knows that if the animal is a jaguar, then it's not a leopard of any sort. More pointedly, she knows that if it's a jaguar, then it's not a leopard that looks just like a jaguar in a jaguar display (if O, then ~T). But Zoe does not know that the ani- mal is not a leopard that looks just like a jaguar in a jaguar display. So, the skeptic invites us to conclude, Zoe doesn't know that it's a jaguar after all. We could multiply examples, but the two we've covered are enough to illus- trate how the skeptic's strategy works. The experiments reported below use vi- Skeptical appeal: the source-content bias | 6 gnettes based on these two examples familiar from the literature on skepticism. 1.2. A theory in two parts Here is one theory about why the classical skeptical argument can seem so po- tent. The theory has two parts. On the one hand, people view perception as a more likely source of knowledge than inference. That is, other things being equal, people more readily classify a belief as knowledge when it's based on observation than when it's based on inference from background knowledge. On the other hand, people view positive inferential belief as a more likely candidate for knowl- edge than negative inferential belief. That is, other things being equal, an infer- ential belief that something is the case is more likely to be classified as knowledge than an inferential belief that something is not the case. If true, these two points can explain the classical skeptical argument's force. First, the argument gets us to focus on what seems like an inferential belief. We're left to think that observation is of no further help, so the agent in question is left to infer the relevant proposition from prior experience and background knowledge. Second, the argument gets us to focus on whether something is not the case, so the inferential belief in question has negative content. On this theory, it's possible that the appeal of skepticism has nothing special to do with either the form of argument that the skeptic employs or the cleverness of the skeptic's tricky alternative scenarios. Rather, it could just be that skepticism's appeal is due to the fact that we're heavily biased against classifying negative inferential beliefs as knowledge. Both experiments below were designed to help evaluate these possibilities. Experiment 1 examines the effect of two factors on knowledge denial in contexts where skeptical possibilities are explicitly raised and considered. The two factors are a belief's source, perceptual versus inferential, and a belief's content, positive 7 | John Turri versus negative. If my hypothesis is correct, then we should see high rates of knowledge denial precisely in cases of negative inferential belief. This is in fact what we observe. Experiment 2 focuses in on inferential belief specifically and again examines the effect of negative versus positive content on people's willing- ness to deny knowledge. Again we see that negative inferential belief is evaluated more harshly than positive inferential belief, even when each is based on a long and unbroken track record of evidence. Experiment 2 also accomplishes something further. The skeptic focuses only on the ordinary claim (O) and the denial of the tricky alternative scenario (~T); he draws skeptical conclusions based this comparison and invites us to do the same. It might seem that the difficulty here stems from something about denying this particular alternative. But the difficulty might instead stem from denying this particular alternative. To test between these possibilities, Experiment 2 ex- amines rates of knowledge attribution for O and ~T alongside those for the denial of O (i.e. ~O). The results suggest that skeptic induces doubt not because his al- ternative is especially difficult to rule out, but rather because the focus shifts from affirmative to negative content. My hypothesis about the source of skepticism's allure can be motivated in light of two substantial bodies of psychological research. On the one hand, re- searchers have found that people exhibit an "anti-inference bias" and are more comfortable relying on direct perceptual evidence, even when the perceptual evi- dence is acknowledged to be less reliable than the inference (Zamir, Rito & Teich- man, in press). Young children are apt to attribute knowledge to subjects with perceptual access to a fact, (Pillow, 1989), but they are often reluctant to attribute knowledge based on simple valid inferences (Sodian & Wimmer 1987). Evidence from comparative psychology suggests that nonhuman animals, including chim- panzees (Povinelli & Eddy, 1996; Call & Tomasello, 2008), bottlenose dolphins (Reiss, 2001), domestic dogs (Horowitz, 2008), and several bird species (Dally, Skeptical appeal: the source-content bias | 8 Emery & Clayton, 2005; Keefner, 2013) attribute mental states to conspecifics, and that these attributions are influenced by what the conspecific has perceptual access to. On the other hand, decades of behavioral research show that it requires more effort to represent and perform computations over negations than affirma- tions (see Conclusion for references). Moreover, increased effort can be expected to diminish confidence in the truth of a claim (Reber & Schwarz, 1999; Oppen- heimer, 2008), and since knowledge requires truth, this could in turn be expected to increase rates of knowledge denial. In addition to the fact that my hypothesis can be grounded in prior psycho- logical findings, it is novel in two respects. First, it marshals those findings in or- der to diagnose the psychological source of a specific, perennial philosophical co- nundrum.1 Second, it posits an interaction effect of a belief's source and content on judgments about knowledge. While prior research has noted the effects of be- lief source and negative content, respectively, the interaction of these two factors has not been documented. Prior influential work in cognitive science has made progress in identifying psychological mechanisms and processes by studying moral cognition through the lens of longstanding philosophical disputes in ethics, especially those motivated by poignant thought experiments involving moral dilemmas (e.g. Greene et al. 2001; Cushman & Greene 2012). If my hypothesis is correct, then the same could be true of studying cognitive evaluations through the lens of classical skeptical challenges. 1 Thanks to an anonymous reviewer for suggesting language along these lines. 9 | John Turri 2. Experiment 1 2.1. Method 2.1.1. Participants Participants (N = 607, 204 female, aged 18–69, mean age = 29.68 years) were re- cruited and tested using an online platform (Amazon Mechanical Turk + Qualtrics) and compensated $0.30 for approximately 2 minutes of their time. Participation was restricted to those residing in the United States and 97 percent reported English as a native language. Participants were not allowed to re-take the survey; repeat participation was prevented by screening AMT Worker IDs. They filled out a brief demographic survey after testing. I excluded data from 32 participants who failed comprehension questions. Including data from these par- ticipants didn't affect the pattern of results reported below. 2.1.2. Materials and procedure Participants were randomly assigned to one of eight conditions in a 2 (Story: Car, Specimen) × 2 (Content: Negative, Positive) × 2 (Source: Inference, Perception) between-subjects design. Participants in each condition read a different story. Two different storylines were used to ensure that the results weren't due to super- ficial features of a particular case. The stories were based on widely discussed ex- amples in the literature on skepticism (see section 1.1). For each storyline, the source and content of the protagonist's belief was varied similarly. The basic storyline for Car featured an office worker, Maxwell, who parked his car in the parking garage when he arrived at work a while ago. Now it's lunchtime and Maxwell and his assistant are looking for a document. Maxwell suspects that he left the document in his car. Maxwell's assistant asks him where his car is parked and, in the process, points out, "It's not unheard of for cars to be Skeptical appeal: the source-content bias | 10 stolen." The Content factor varies which aspect of the assistant's speech Maxwell focuses on: where the car is parked versus whether the car has been stolen. Par- ticipants in the Negative conditions were asked whether Maxwell knows that his car was not stolen. Participants in the Positive conditions were asked whether Maxwell knows that his car is parked in the spot he parked in this morning. The Source factor varies what source Maxwell bases his answer on. In the Inference conditions, Maxwell thinks for a moment before answering, unaided by observa- tion. In the Perception condition, Maxwell looks out the window before answer- ing. Here is the story (manipulations bracketed and separated by a slash): When Mr. Maxwell arrives at work in the morning, he always parks in one of two spots: C8 or D8. Half the time he parks in C8, and half the time he parks in D8. Today Maxwell parked in C8. It's lunchtime at work. Maxwell and his assistant are up in the archives room searching for a particular document. Maxwell says, "I might have left the document in my car." The assistant asks, "Mr. Maxwell, is your car parked in space C8? It's not un- heard of for cars to be stolen." Maxwell [thinks for a moment / looks out the window] and then responds, "[No, my car hasn't been stolen / Yes, my car is in C8]." After reading the story, participants answered two comprehension questions and a test question about what Maxwell knows (options in parentheses) 1. Maxwell parked in _____. (C8/D8) 2. Maxwell is in the _____. (archives room/parking garage/cafeteria) 3. Maxwell _____ that his car [is parked in C8 / has not been stolen]. (knows/only believes) The basic storyline for Specimen featured an avid zoo patron, Michelle, whose favorite exhibit is "The Big Cat Exhibit." Over thousands of observations, the animal in the exhibit has always been a jaguar. The Source factor varies 11 | John Turri whether Michelle judges the animal based on perception (Perception) or based on an inference unaided by observation (Inference). The Content factor varies whether Michelle thinks that the animal is a jaguar (Positive), or that the animal is not a leopard (Negative). Participants in the Positive condition were asked whether Michelle knows that the animal is a jaguar; in the Negative condition they were asked whether Michelle knows that it's not a leopard. Here is the story: Michelle has visited the city zoo every day for the past ten years. Her fa- vorite exhibit is The Big Cat Exhibit. Over thousands of observations, the animal in this exhibit has always been a jaguar. Today [Michelle must stay home and can't visit the zoo because she sprained her ankle. While relax- ing on the couch / when Michelle left home to visit the zoo, she almost sprained her ankle. While looking at the animal in the exhibit], Michelle thinks, "The animal in the Big Cat Exhibit today is [a jaguar / not a leop- ard]." And she is right: it is [a jaguar / not a leopard]. After reading the story, participants were asked two comprehension ques- tions and a test question: 1. The animal _____ a jaguar. (is/is not) 2. Michelle is _____. (at home/at the zoo) 3. Michelle _____ that the animal is [a jaguar / not a leopard]. (knows/only believes) Participants who failed a comprehension question were excluded from the analysis. Questions were always asked in the same order and response options were always rotated randomly. The story remained at the top of the page throughout the survey. 2.2. Results An initial omnibus regression was used to determine whether knowledge denial Skeptical appeal: the source-content bias | 12 was predicted by storyline or participant gender. In line with previous research on knowledge ascriptions (Wright, 2008; Turri, 2013; Nagel et al., 2013; Fried- man and Turri, under review), participant gender didn't predict knowledge de- nial. There was no main effect of participant gender (Wald = 0.012, df = 1, p = . 911, n.s., all tests two-tailed unless otherwise noted) and no interaction with Con- tent (Wald = 2.11, df = 1, p = .146), Source (Wald = 0.03, df = 1, p = .863), or Story (Wald = 0.534, df = 1, p = .465). Similarly, logistic regression showed that there was no main effect of Story (Wald = 1.161, df = 1, p = .281, n.s.) and no in- teraction with Content (Wald = 1.03, df = 1, p = .310, n.s.) or Source (Wald = 0.021, df = 1, p = .885). Because gender and story had no effect, the analyses that follow collapse across these factors. Binary logistic regression was performed to assess the impact of Source and Content on the likelihood that participants would deny knowledge (Table 1). The model contained Source, Content, and the interaction of Source and Content as predictor variables and knowledge denial as the outcome variable. (Preliminary analysis was conducted to ensure no violation of multicollinearity assumptions.) In light of the hypothesis proposed in section 1.2, I expected two things. First, there would be a main effect of Source, with inferential belief predicting higher rates of knowledge denial. Second, there would be a significant interaction be- tween Source and Content, with negative content more strongly predicting higher rates of knowledge denial for inferential belief. Both predictions were true (Table 1). The full model was statistically signifi- cant, χ2(3, N = 607) = 93.82, p < .001. It explained between 14.3% (Cox and Snell R Square) and 19.4% (Nagelkerke R Square) of the variance in knowledge denial, and it correctly classified 70% of cases. Source of belief made a unique statisti- cally significant contribution to the model. By changing the source of the protago- nist's belief from perception to inference, the odds of denying knowledge in- creased by 280% (or a factor of 2.8). Content of belief did not make a unique sta- 13 | John Turri tistically significant contribution to the model. Crucially, there was a significant interaction between the source and content of belief: by changing the content of the protagonist's belief from positive to negative, the odds of denying knowledge increased more for inferential belief than for perceptual belief (by a factor of 2.33). Table 1. Experiment 1. Logistic regression predicting knowledge denial. (Reference class for Source: Perception. Reference class for Content: Positive.) B S.E. Wald df p Odds Ratio 95% C.I. for Odds Ratio Lower Upper Source 1.03 .26 16.13 1 <.001 2.8 1.70 4.64 Content .349 .27 1.69 1 =.194 1.42 .84 2.40 Source*Content .847 .36 5.43 1 =.02 2.33 1.14 4.76 Constant -1.33 .20 44.77 1 <.001 .264 As a further way of clarifying and illustrating the results, I report some pair- wise comparisons among the cells. If the hypothesis proposed in section 1.2 is correct, then we would expect three things. We would expect knowledge denial to be (1) significantly higher in Negative Inference than in Positive Inference, (2) significantly higher in Positive inference than in Positive Perception and Negative Perception, but (3) no different between between Positive Perception and Nega- tive Perception. All three expectations are met (Figure 1). First, rate of knowledge denial was higher in Negative Inference (N = 145, 71%) than in Positive Inference (N = 155, 42.6%), Fisher's exact test, p < .001, Cramer's V = .287. Second, knowledge de- nial in Positive Inference was higher than in Positive Perception (N = 153, 20.9%), Fisher's exact test, p < .001, Cramer's V = .233, as well as Negative Per- ception (N = 155, 27.3%), Fisher's exact test, p = .006, Cramer's V = .161. Third, rate of knowledge denial didn't differ between Positive Perception and Negative Skeptical appeal: the source-content bias | 14 Perception, Fisher's exact test, p = .230, n.s. Finally, binomial tests revealed that only in Negative Inference did partici- pants deny knowledge at rates exceeding chance (p < .001). By contrast, knowl- edge denial was trending below chance in Positive Inference (p < .077) and fell far below chance in both Positive Perception and Negative Perception (ps < .001). Fig. 1. Experiment 1. Denial of knowledge across conditions. 2.3. Discussion Three main findings emerge from this study. First, participants were more likely to deny knowledge in cases of inference than in cases of perception. An inferen- tial belief is much less likely than a perceptual belief is to be classified as knowl- edge. Second, a negative inferential belief is much less likely than a positive infer- ential belief is to be classified as knowledge. The cumulative result is that nega- tive inferential belief suffers a double-deficit. The interaction effect in the regres- sion model is particularly good evidence for this double-deficit. (For replications 15 | John Turri of this interaction effect, see Turri under review.) Third, only when evaluating a negative inferential belief did participants deny knowledge at rates exceeding chance. In each of the other three conditions - when evaluating positive percep- tual belief, negative perceptual belief, and positive inferential belief - partici- pants ascribed knowledge at rates exceeding chance. Importantly, we observed these patterns while using stories directly based on influential cases from the contemporary literature on skepticism. Thus the results suggest that skeptics instill doubt in us to the extent that they get us to focus on inferential belief with negative content. Skeptical arguments themselves could function simply to shift our focus in that way, rather than persuading us in virtue of their logic. These results suggest that the skeptic's alternative scenarios - "your car might have been stolen," "the animal might be a leopard that looks just like a jaguar" - aren't especially challenging to rule out. That is, it's possible that the skeptic has simply alighted on a class of beliefs that we're antecedently inclined to evaluate especially harshly. A second study was designed to investigate this possi- bility further by examining whether ruling out the skeptic's alternatives is any more difficult than ruling out more routine claims. 3. Experiment 2 The skeptic singles out the logical implications of propositions we ordinarily take ourselves to know. If we ordinarily take ourselves to know O, and we know that O entails ~T, then we should also at least be in a position to know ~T. For example, if the animal is a jaguar, then it's not a leopard of any sort. So if you know that the animal is a jaguar, then you should also be in a position to know that it's not a leopard. By contrast, the skeptic doesn't consider whether knowing O is any eas- ier than knowing its negation (~O). If the skeptic really has identified a special Skeptical appeal: the source-content bias | 16 problem, then it should be harder to know ~T than it is to know ~O (other things being equal). In other words, it's possible that the key difference might not be be- tween O and T but rather between negative and affirmative contents. The Specimen cover story is particularly well suited to investigate this. We ordinarily take ourselves to know that the animal in the display is a jaguar. And, obviously, if it's a jaguar, then it's not a leopard. But jaguars and leopards look very similar. Do we know that it's not a leopard? As we saw in Experiment 1, when the agent is able to observe the animal, people tend to say that she knows that it's not a leopard. By contrast, when she doesn't observe the animal but in- stead draws an inference, people deny that she knows that it's not a leopard. Peo- ple denied knowledge even though her inference was based on a long and unbro- ken track record: over many years and thousands of observations, the animal in the display has always been a jaguar. But suppose that instead of always being a jaguar, the animal in the display had never been a jaguar. Based on this long and unbroken track record, will peo- ple be any less harsh in evaluating an inferential belief that the animal is not a jaguar? If the skeptic has identified a special problem, then it should be viewed as harder to know (~T) that the animal is not a leopard (based on a long and unbroken track record of its being a jaguar) than it is to know (~O) that the animal is not a jaguar (based on a long and unbroken track record of its not being a jaguar). By contrast, if my earlier hypothesis is correct, then people will view those two propositions as equally difficult to know. In other words, rates of knowledge de- nial for those two claims will be equally high because they are both inferential 17 | John Turri and negative. Moreover, rates of knowledge denial for those two claims should be significantly higher than for this claim, which is inferential but positive: (O) that the animal is a jaguar (based on a long and unbroken track record of its being a jaguar). The present study directly tests these suggestions. 3.1. Method 3.1.1. Participants Three hundred and five new participants (87 female, aged 18-78, mean age = 28.16 years) were tested. They were recruited and compensated the same way as in Experiment 1. Ninety-eight percent reported English as a native language. I ex- cluded data from 11 participants who failed comprehension questions. Including data from these participants didn't affect the pattern of results reported below. 3.1.2. Materials and procedure Participants were randomly assigned to one of three conditions: Positive Jaguar, Negative Leopard, and Negative Jaguar. Participants in each condition read a dif- ferent story. The stories for the Positive Jaguar and Negative Leopard conditions in this experiment are very similar to the Specimen stories for the Positive Infer- ence and Negative Inference conditions in Experiment 1. In the story for Positive Jaguar, the animal has always been a jaguar and Michelle thinks that it's a jaguar today too. In the story for Negative Leopard, the animal has always been a jaguar and Michelle thinks that it's not a leopard today either. The story for the Negative Jaguar condition is similar except that this time the animal in the display has never been a jaguar and Michelle thinks that it's not a jaguar today either: Michelle has visited the city zoo every day for the past ten years. Her fa- Skeptical appeal: the source-content bias | 18 vorite exhibit is The Big Cat Exhibit. Over thousands of observations, the animal in this exhibit has never been a jaguar. Today Michelle must stay home and can't visit the zoo because she sprained her ankle. While relax- ing on the couch, Michelle thinks, "The animal in the Big Cat Exhibit today is not a jaguar." And she is right: it is not a jaguar. There was one difference in procedure between this experiment and Experi- ment 1: this time participants were also asked to rate their confidence in their an- swer to the knowledge question. Responses were collected on a 1 ("not at all con- fident") to 10 ("completely confident") scale. This was done to check for subtle differences of opinion not captured by the dichotomous measure. Otherwise, the questions and procedure for this experiment are the same as for Experiment 1. 3.2. Results I made three predictions about the rate of knowledge denial: (1) it would vary across the conditions, (2) it would be lower in Positive Jaguar than in each of the other two conditions, (3) it would not differ between Negative Jaguar and Nega- tive Leopard. All three predictions were true. First, the rate of knowledge denial varied across the conditions, χ2(2, N = 305) = 8.31, p = .016, Cramer's V = .165. Second, pairwise comparisons revealed that the rate of knowledge denial was lower in Positive Jaguar (N = 100, 53%) than in Negative Jaguar (N = 103, 71.8%), Fisher's exact test, p = .006, Cramer's V = .195, and lower in Positive Jaguar than in Negative Leopard (N = 102, 66.7%), Fisher's exact test, p = .033, one-tailed, Cramer's V = .139. Third, rate of knowledge denial didn't differ between Negative Jaguar and Negative Leopard, Fisher's exact test, p = .452, n.s. Figure 2 visualizes these results. 19 | John Turri Fig. 2. Experiment 2. Denial of knowledge across conditions. Binomial tests revealed that rate of knowledge denial was significantly above chance in both Negative Jaguar and Negative Leopard (ps < .001). By contrast, it was no different from chance in Positive Jaguar (p = .617). Participants were also asked to rate their confidence in their answer to the knowledge question. A one-way analysis of variance detected no difference in confidence scores across the conditions: Positive Jaguar, M = 8.67, SD = 1.68; Negative Jaguar, M = 8.77, SD = 1.34; Negative Leopard, M = 8.51, SD = 1.60; F(2) = .715, p = .49, n.s. 3.3. Discussion Two main things emerge from this study. First, the results replicate a main find- ing from Experiment 1: negative inferential belief is evaluated more harshly than positive inferential belief, even when each is based on a long and unbroken track record of evidence. Second, the results support the hypothesis that the skeptic ex- ploits an evaluative bias against negative inferential beliefs. The skeptic's tricky Skeptical appeal: the source-content bias | 20 alternative scenarios aren't necessarily especially difficult to rule out. For in- stance, in this study participants were just as unwilling to ascribe knowledge to Michelle that the animal was not a jaguar (~O) as they were to ascribe knowledge that the animal was not a leopard (~T). By contrast, participants were much more willing to ascribe knowledge that the animal was a jaguar (O). In short, the key difference is not be between O and T but rather between negative and affirmative contents. Once again it seems that the skeptic succeeds in getting us to seriously doubt ourselves only in cases of negative inferential belief. 4. Conclusion Certain skeptical arguments have an uncanny ability to simultaneously attract and repel our intellects. They use premises that we find plausible, only to end with conclusions that we find absurd. What explains our ambivalent relationship to these arguments? Given that nearly no one actually accepts the skeptical con- clusions, why do we pay any attention to them? Why is skepticism, despite its im- plausibility, a staple of both intellectual and popular culture? Philosophers have proposed many explanations. Perhaps it's because we want to know things and understand what knowledge requires, but we implicitly recognize that we can't meet those requirements (Unger, 1975). Or perhaps there are deep tensions in our concept of knowledge, or in our pursuit of it, which lead us to vacillate on whether we can ever know anything (Stroud, 1984; Nagel, 1986: ch. 5). Or perhaps we misunderstand the relationship between the things we ordi- narily know and the things the skeptic says we can't know: maybe we don't need to rule out skeptical alternatives in order to know ordinary things about the world around us (Dretske, 1970; Nozick, 1981). Or perhaps the verb 'knows' is semanti- cally context-sensitive and the skeptic is able to manipulate the conversational 21 | John Turri context so that he speaks truthfully when he says we "don't know" something (Cohen, 1988; DeRose, 1995; Lewis, 1996). Or perhaps the skeptic exploits facts about the pragmatics of knowledge discourse or the social function of knowledge attributions (Turri, 2010; Turri, 2012; Turri, in press). But before drawing sweeping conclusions about the nature of knowledge or proposing revisionary semantic hypotheses, we might do well to identify psycho- logical factors that contribute to skepticism's enduring appeal. I've developed a version of this last suggestion in this paper. Our findings from two studies support several conclusions. First, the classic skeptical argument poses a greater threat to inferential belief than perceptual be- lief. Second, inferential belief with a negative conclusion is judged especially harshly and is unlikely to be classified as knowledge. Third, it turns out that clas- sic skeptical arguments owe a good deal of their potency to this evaluative bias against negative inferential beliefs, namely, the source-content bias. Before the skeptic even shows up, people confidently claim that such beliefs don't count as knowledge. When the skeptic finally does show up to make his case, it probably does not, as some philosophers claim, "come as a surprise" - it is not "startling" or "shocking" to hear - that such beliefs don't seem to be knowledge. The skeptic has not "pointed out that we do not know things we would have confidently said we knew" (Nozick 1981: 202). People routinely deny that such beliefs count as knowledge. It is not, in the first place, some deep fact about the nature of knowl- edge or the skeptic's ingenuity that invites skepticism. It's our psychology. The bias against negative content for inferential belief specifically is surpris- ing and further work is required to better understand it. Voluminous behavioral research shows that it is more complicated and effortful to represent negation than affirmation (Wason, 1961; Wason, 1965; Gough, 1966; Slobin, 1966; Mac- Donald & Just, 1989; Evans, Newstead & Byrne, 1993; Kaup, 2001; Hasson & Glucksberg, 2006; Stupple & Waterhouse, 2009), and recent work in cognitive Skeptical appeal: the source-content bias | 22 neuroscience has begun uncovering the neural signatures of this difference (Christensen, 2009; Kumar, Padakannaya, Mishra & Khetrapal, 2013). Accord- ingly, one might expect knowledge ascriptions for positive claims to be higher in general, whether the source of belief is inference or perception, because "any variable that increases experienced ease of processing is also likely to increase judgments of truth" (Reber & Schwarz, 1999: 342). But this is not what we ob- served. Instead, we observed significantly lower rates of knowledge attribution for negative inferential beliefs but no corresponding asymmetry for perceptual beliefs. Recent research suggests that a readily accessible schema for accommodating negative information promotes greater fluency (Mayo, Schul & Burnstein, 2004). For example, "it is not warm" can be more readily processed than "it is not wary" because the familiar "cold" accommodates "not warm," whereas no common ad- jective as readily accommodates "not wary." However, in the studies reported here, the protagonist's negative belief had the same content whether it was formed perceptually or inferentially, so a more accessible opposing conceptual schema can't explain the asymmetry. Thus it's possible that the source of information also facilitates comprehension of negative information. Perhaps people more fluently process negative information if the informational source is percep- tual, thereby raising rates of knowledge ascription. In other words, in addition to features of informational content enhancing fluency, perhaps features of infor- mational source can too. This last suggestion gains some plausibility from a growing body of work on the perceptual simulation theory of linguistic comprehension. According to this view, when comprehending a text, people construct a mental simulation of the situation it describes (Johnson-Laird, 1983; Graesser, Millis & Zwaan, 1997) and this mental simulation shares the representational format of perception and ac- tion (Zwaan, 2004; Bianchi, Savardi, Burro & Torquati, 2011; see also Barsalou, 23 | John Turri 1999). Interestingly, one line of evidence for this view comes from a series of studies on negation (Kaup, 2001; Kaup & Zwaan, 2003; Kaup, Yaxley, Madden, Zwaan & Lüdtke, 2007; Zwaan & Percher, 2012 replicates relevant results using Amazon Mechanical Turk). If people comprehend negations by perceptually sim- ulating them, then this might help explain why negation affects the evaluation of inferential belief differently than perceptual belief. For when the protagonist in the story forms her belief perceptually, her mode of cognition closely matches the mode in which participants simulate and thereby comprehend the case. By con- trast, when the protagonist forms her belief non-perceptually, her mode of cogni- tion mismatches the mode in which participants simulate the case. Participants asked to evaluate a negative inferential belief are thus required to dissociate two modes of cognition, their own and the protagonist's, resulting in a more compli- cated theory-of-mind task. This in turn could inhibit fluency and thus depress rates of knowledge attribution. Regardless of whether this suggestion explains the results observed above, the experiments reported here provide evidence for two main conclusions. 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