SCEPTICISM ABOUT OTHER MINDS Anil Gomes Trinity College, University of Oxford To appear in D. Machuca & B. Reed (eds.) Skepticism: From Antiquity to Present [submitted 2013] In this paper I distinguish two ways of raising a sceptical problem of others' minds: via a problem concerning the possibility of error or via a problem concerning sources of knowledge. I give some reason to think that the second problem raises a more interesting problem in accounting for our knowledge of others' minds and consider proposed solutions to the problem. 1. Introduction Scepticism about others' minds is the claim that we have no knowledge of other people's mental lives. This can sometimes strike us as a manifest truth. We occasionally find ourselves in situations where we feel cut off from what other people think and feel, and when this happens, it can seem like the bringing to the surface of a cognitive estrangement which is always there. Thus Lily Briscoe, in Virginia Woolf's To the Lighthouse, expresses frustration at her inability to enter into 'the chambers of [another's] mind and heart'. 'How, then, she had asked herself, did one know one thing or another about people, sealed as they were?' (p.44). Such knowledge is unattainable, she concludes. Yet such scepticism should also strike us as strange and revisionary. For we do take ourselves to know many things about what other people think and feel. I know that Arun hopes for a Labour victory; I know that Priya is 2 angry with her sister; I know that Ayesha suffers from back pain. This knowledge is part of our everyday dealings with other people. And it is a central part of many of those relationships which give our lives significance: part of what makes Ayesha such a good friend is that she knows when a particular conversation topic is upsetting those around her and moves to change the topic. Scepticism about others' minds conflicts with our ordinary conception of our relation to other people. My aim in this essay is to consider what reason we have to endorse scepticism about others' minds. I'll argue that we need to distinguish two distinct ways in which one might motivate such scepticism and provide some reason for focusing on the second of these motivations. I'll set out some of the responses to the sceptical problem before providing my own sense of which avenues of further exploration will be most fruitful. An initial point of clarification: which knowledge claims does scepticism about others' minds rule out? I take the knowledge in question to be any claim which ascribes a mental feature to another person. Since the category of a mental feature is so broad, this is itself an expansive category: the ascription of beliefs, feelings, character traits, emotions, actions and activity all fall under the heading of mental features, broadly construed. Those who write on this topic tend to concentrate on our knowledge of what other people believe and feel. I will follow that restriction in what follows. But we should not assume that the same considerations apply to our knowledge of each and every member of this diverse class. 2. The Problem of Error One common way to raise a sceptical problem about others' minds is by appeal to cases of pretence (e.g. [McDowell 1982], drawing on a tradition emanating from [Wittgenstein 1992]). Cases of pretence are ones in which someone presents themselves as having a mental feature which they in fact lack. A judgement based on how things seem in such cases will result in a false belief. But – the sceptic argues – your evidential basis for this judgement is the same as that in the case in which you judge someone to have a mental feature which they do have. Since your evidence does not suffice for knowledge in the bad case, it cannot suffice for knowledge in the good case. 3 Note first that there is something odd about using pretence as an exemplar of this sceptical scenario. Another person can only pretend to have a mental feature which she lacks if she has other mental features such as a desire to simulate and the belief that this is the way to do so. For this reason, a case of pretence does not support the claim that we have no knowledge of others' minds for I can reason as follows: either she is pretending or she is not. If she is not pretending, then she really does instantiate the mental feature which she appears to instantiate. If she is, then she must have some other beliefs and desires. In either case, she has a mind. The case of pretence is ineffective in motivating complete scepticism about others' minds for the same reason that Descartes judged the evil demon hypothesis ineffective in motivating scepticism about his own existence. (I owe this point to Paul Snowdon.) This implication is avoided by choosing an alternative sceptical scenario, such as one in which those around us are robots or philosophical zombies. I will refer to such cases as ones of error, understood as ones in which it seems to you as if someone has a particular mental feature which they in fact lack. Unlike cases of pretence, certain cases of error are compatible with it not being possible for a subject to have knowledge of others' minds. With this in mind, we can formulate the sceptic's argument. Let 'o is F' stand for the ascription to another of a mental feature; let 'the bad case' designate a case in which it seems to you as if someone has a particular mental feature which they in fact lack and you judge mistakenly that o is F; let 'the good case' designate the case in which it seems to you as if someone has a particular mental feature which they do in fact have and you judge accurately that o is F. Let two cases be phenomenally indistinguishable when things are phenomenally the same for the subject in the two cases. Then we can reason as follows: 1. The good case and the bad case are phenomenally indistinguishable. 2. If the good case and the bad case are phenomenally indistinguishable, then the subject's evidence is the same in the two cases. 3. If the subject's evidence is the same in the two cases, then the epistemic status of her belief is the same in the two cases. 4. In the bad case, you don't know that o is F. 5. In the good case, you don't know that o is F. (from 1,2,3,4) 4 This argument generalises to take in all mental phenomena which fall under cases of error. It can thus be used to show that we don't have any knowledge of other people's mental lives. How should an anti-sceptic reply to this argument? (4) follows from the assumption that knowledge entails truth. That leaves us with (1), (2) and (3). Some forms of epistemological externalism reject (3): they hold that factors external to a subject can affect the epistemic status of her beliefs without changing her evidence. Evidential externalist responses reject (2): they hold that the evidence available to a subject can differ even when things seem to her to be the same. Disjunctive responses reject (1): they hold that how things seem to the subject is not the same in the two cases for in the good case, 'the appearance that is presented to one... is a matter of the fact itself being disclosed to the experiencer.' [McDowell 1982, p.387]. The rejection of (1) is compatible with the good and bad case being subjectively indiscriminable – in the sense that in both cases one can't know, through reflection, that one is not in the good case – but subjective indiscriminability does not entail phenomenological indistinguishability. I won't evaluate these responses here. What should be clear, from the way in which I've set up the problem, is that this style of sceptical problem arises in many domains. In the case of perceptual knowledge, the bad case is one of illusion or hallucination. In the case of knowledge of the past, it is one in which the world came into existence five minutes ago with all my apparent memories included. Sceptics claim that the indistinguishability of such cases from genuine cases undermines our claims to knowledge. This form of argument generalises. Furthermore, the forms of response mentioned above also apply in each of these domains. Evidential externalists about perceptual knowledge hold that the evidence in the good case is not the same as the evidence available in the bad case; disjunctive responses hold that how things seem to one is different in the two cases. This fact of wider application is made more salient by the fact that John McDowell's influential response to the sceptical problem arises in the context of drawing a link between the problem of other minds and the problem of perceptual knowledge. Once one has noted this generalisation, it is hard not to sympathise with Fodor's comment that '[i]t's gotten harder to believe that there is a special problem about the knowledge of other minds (as opposed to other anything elses)' (1994, p.292) 5 What are the implications for scepticism about others' minds? My provisional conclusion is that we have seen nothing, thus far, to motivate the thought that we have a distinctive philosophical problem of other minds – one which turns on aspects of our mentality and its expression to others. This conclusion is only provisional because it may be that the plausibility of any particular application of the responses mooted above will depend on facts specific to the domain in question: perhaps a disjunctive solution is plausible for perceptual knowledge and not knowledge of others' minds, say. But, as a general moral, we can say that what we have here is a problem about knowledge, one which can be raised in the case of our knowledge of others' minds. And whilst this is a way of motivating scepticism, it doesn't motivate a distinctive scepticism about others' minds. 3. The Problem of Sources In the rest of this essay, I want to motivate an alternative way of raising a sceptical problem about others' minds. It is a way of raising the problem which I think is both more faithful to the history of the problem as discussed in twentieth-century analytic philosophy and turns on issues distinctive to our mentality. Let me start with the history. When one looks at discussions of the problem of other minds at the start of the twentieth-century, issues about pretence and deception are largely absent from the debate. Instead, the starting point is a supposed contrast between the way we know our own minds and the way in which we know the minds of other people. Here are two examples, spanning the first half of the twentieth-century. First, G.F. Stout, introducing his discussion of knowledge of others' minds by means of an implied contrast with the way in which we know our own mind: To introspect is to attend to the workings of one's own mind... Noone can directly observe what is passing in the mind of another. [Stout 1898, p.14, p.20] Second, A.J. Ayer, characterising the problem of other minds: We may take as our starting-point the propositions that I can have direct knowledge of my own experiences and that I cannot have direct knowledge of anyone else's. [Ayer 1953, p.193] 6 Each of these writers adverts, in different ways, to a certain contrast between the way in which we know our own mind and the way in which we know the minds of others. The exact nature of this contrast is largely unimportant except for dialectical purposes. What matters, for each of them, is that the contrast shows up a problem in accounting for the source of our knowledge of other's mind. The thought is this: we have a way of knowing about our own mental lives. But this source of knowledge cannot be used to find out about the mental life of another person. If we do not have a source of such knowledge, then we do not have knowledge of others' mental lives. We can best formulate this line of thought as an antinomy of three claims: (S1): If you know that p, then there is a means by which you know that p. (S2): There is no means by which one can know truths about another's mind. (S3): We know truths about another's mind. These three claims are jointly incompatible. From (S1) and (S3) it follows that there is a means by which we know about other people's mental lives; this is in contradiction with (S2). Scepticism about others' minds is a rejection of (S3): we have no knowledge about other people's mental lives. Most participants to the debate reject (S2): it is certainly the most obviously contestable and I will focus on it in what follows. But it will be useful to say something about (S1), a claim which is rarely articulated but which I take to be assumed in the debate. In his paper 'Other Minds' (1946), J.L. Austin notes whenever someone makes a claim to knowledge, it is appropriate to ask 'How do you know?'. Timothy Williamson agrees (2000, pp.252-3) and Quassim Cassam calls this 'something like a conceptual truth' (2009, p.112). The natural way of taking this question is as requesting identification of the source or means of one's knowledge. The linguistic fact about the appropriateness of a certain question reflects a metaphysical fact about knowledge: namely, that if someone knows that p, then there is a means by which she knows it. 7 Challenges to (S1) arise in cases in which the 'How do you know?' question is claimed to be inappropriate, thus identifying potential counterexamples to the thesis. Consider the assertion 'I am in pain'. Certain readers of Wittgenstein have taken the question 'How do you know?' to be inappropriate in response to this assertion. One response is to conclude that it is false to say that a subject knows she is pain. But an alternative, canvassed by Hampshire, is to hold that a subject can know that she is in pain without there being a means by which she knows it (1969, pp.282283). Donald Davidson makes the same claim for other cases of selfknowledge (Davidson 1991, p.212). I will put these challenges to one side. They arise specifically in the context of certain cases of self-knowledge and the considerations adduced do not motivate the failure of (S1) for other types of knowledge. Moreover, (S1) has a great deal of plausibility. If one thinks of states of knowledge as part of the natural world, then there must be a causal story one can tell about how subjects get into them. Those who are sympathetic to some form of naturalised epistemology will hold that telling such a story identifies the means by which a subject knows. Those who want to reject scepticism about others' minds should deny (S2). 4. Perception and Inference Why would one think that there is no means by which we know truths about another's mind? One reason would be if there were some general condition on knowledge which couldn't be met by truths about another's mind. Say, for example, that knowledge requires a causal interaction between a subject's belief and that which is known. This condition has been thought to raise a problem in explaining our knowledge of domains from which we are causally isolated, for example mathematical truths [Benacerraf 1973, p.673f], or moral values [Mackie 1977, p.38-39]. If others' minds were causally isolated from the physical world, then there would be no means by which we could know about them and (S2) would hold. This suggests that (S2) follows from certain conceptions of the mental, such as those on which the mental features are attributes of an immaterial substance causally isolated from the physical world. It may also follow from those conceptions of the mental which deny the existence of immaterial substance but hold that particular mental features such as the 8 qualitative character of consciousness are causally isolated from the physical world. I take it that these conceptions of the mental are neither popular nor attractive so put this motivation of (S2) to one side. The discussion in Ayer and Stout offers us an alternative way of motivating (S2). Consider the way in which we know about our own mental lives. Call this method introspection. It is necessarily first-personal, that is to say, it cannot be used to find out about the mental features of another person. So the source of our knowledge about own mental life is not one which can provide us with knowledge of another's mind. I take this to be the reason why some of those writing on this issue focus on the asymmetry between self-knowledge and our knowledge of others' minds: it shows up the fact that one prevalent source of knowledge of mental features cannot be used to gain knowledge of another's mental life. How, then, do we know about others' minds? Other people and their mental features are aspects of the world around us. And when we think about how we gain knowledge about the external world, there seem to be two broad methods of which we make use: perception and inference. Perceptual knowledge is knowledge based on the basic deliverances of the senses, as when I come to know that the chairs are blue by looking at them. Inferential knowledge is knowledge which takes us beyond what is given in experience, as when I come to know that there was a party at my neighbour's house on the grounds that it is the best explanation of the contents of her recycling bin. Perhaps there are interesting philosophical questions about how exactly we are to distinguish these sources of knowledge, but they look to be distinct. Is our knowledge of others' minds perceptual or inferential? This is where the case for (S2) has been thought to get its bite. For one recurring theme in the literature is that neither of these sources of knowledge can enable us to gain knowledge about another person's mental life. Against perception it is said that we cannot perceive the mind of another person: at best we can perceive her behaviour. So we cannot be said to have perceptual knowledge of her mental life. But against inference it is claimed that this experience of behaviour isn't secure enough to ground an inference to the presence of others' minds. If neither perception nor inference can serve as a source of knowledge of other people's mental lives, then there is a problem in accounting for the source of such knowledge. 9 What reasons are given for ruling out these sources of knowledge? Take perception first. In comparing the perceptual and inferential responses, Price comments that 'it must strike every unprejudiced person that [the perceptual theory] is much the odder of the two... [I]t is extremely paradoxical.' [Price 1931, p.54]. This sense of absurdity is often shared: what would it be to perceive another's mental life? Colin McGinn offers further considerations in support: 'while propositional perceptual reports sometimes seem natural in specifying my cognitive relation to the mental states of another, direct object perceptual reports ('I saw the pain in his foot') seem definitely wrong.' [McGinn 1984, p.123 fn.2]. If this linguistic phenomenon tells us something about the objects of perception, knowledge of others' minds cannot be a form of perceptual knowledge. What about the claim that inference cannot serve as a source of such knowledge? Various arguments have been put forward in support of this claim. It has been claimed that we do not appear to engage in inferential reasoning; that infants and animals can know things about others' minds without possessing the cognitive powers necessary to engage in inference; that we do not know enough about other people's behaviour to provide a sound base for inference [Price 1931, pp.55-56]. More sophisticated objections hold that one cannot engage in inference in cases where it is logically impossible to verify the conclusion, or that the link between behaviour and mind is known only from one's own case, and that this is not a secure enough basis to secure inferential justification [Ryle 1949, pp.15-16; Malcolm 1958, p.969]. If one finds these reasons persuasive, knowledge of others' minds is not a form of inferential knowledge. It is the supposed inadequacies of perceptual and inferential models of knowledge which motivate scepticism about others' minds. Standard responses to this problem opt to deny one or other of these claims: either they claim perception can be a source of knowledge of others' minds, or – as is more common – they claim that the experience of behaviour can ground inferential knowledge about another's mind. Either option amounts to a denial of (S2): there is a means by which we know truths about another's mind. Let us consider each in turn. First, perception. Although it has been the less popular of the two options, the claim that our knowledge of others' minds is a form of perceptual knowledge has been defended throughout the twentieth-century [Duddington 1918; Dretske 1973; McDowell 1982; Cassam 2007a, ch.5; 10 McNeill 2011]. It was a prominent part of the phenomenological tradition and some recent defenders of a perceptual account have drawn on the work of Scheler, Husserl and Merleau Ponty in presenting their proposals [Gallagher and Zahavi 2008; Krueger and Overgaard 2012]. Much of this work is primarily defensive. Consider the following objection to perceptual accounts: other people's mental lives can't be perceived. Therefore our source of knowledge of such lives can't be perception. There are two responses to this claim in the literature. Drestke and Cassam accept the premise of the objection whilst rejecting its conclusion: they hold that one can see that another person is angry and thus come to know that another person is angry without seeing her anger. Others hold that our perception of others extends beyond their behaviour to take in their mentality: other people's mental lives are perceptible. In defending the first option, Dretske offers the following analogy: one can see that a piece of metal is hot without seeing its heat. Similarly, one can see that another person is angry without seeing her anger. These claims rely on the account of epistemic seeing – seeing that something is the case – set out in [Dretske 1969]. If one accepts Dretske's account of epistemic seeing, it is possible to see that someone is angry and thereby come to know that she is angry without seeing her anger. For criticisms and discussion of Cassam and Dretske on this point, see [Gomes 2010; McNeill 2011]. The second form of response holds that certain mental features can be seen. This is sometimes supported, contra McGinn, by appeal to the facility of certain perceptual locutions in reporting the source of our knowledge of others' minds: 'I heard the anger in her voice'; 'I saw the pain in her eyes' [Green 2007; Stout 2010]. The claim can been developed in different ways: some hold that mental states are expressed in behaviour and thus perceptible [Green 2007]; others hold that behaviour is partly constitutive of mentality, such that in seeing someone's behaviour one sees their mental features [Krueger and Overgaard 2012]. These claims turn on wider issues in the philosophy of mind about the relation between mental states and behaviour. The above comments are defensive: they aim to defend the perceptual model against a natural and prominent objection. Are there any positive 11 reasons for adopting a perceptual account of our knowledge of others' minds? One can find two lines of thought in the literature. The first is that it seems to us as if our access to other people's mental lives is perceptual and that we should take this appearance seriously. This is particularly stressed by those who draw on the phenomenological tradition, e.g. [Krueger and Overgaard 2012, p.248], but it might also be thought to be part of John McDowell's influential presentation of a perceptual account. As McDowell puts it, '[w]e should not jib at, or interpret away, the commonsense thought that... one can literally perceive, in another person's facial expression or his behaviour, that he is in pain, and not just infer that he is in pain from what one perceives' [McDowell 1978, p. 305]. This explains why the bulk of this literature is primarily defensive: if our starting point is the commonsense thought that our access to others' minds is perceptual, then all we need do is defend that starting point against objections. The second motivation relates to what is sometimes called the conceptual problem of other minds. This essay is concerned with the epistemological problem of other minds, the problem of accounting for our ability to know about others' mental lives. The conceptual problem of other minds concerns the problem of explaining our ability to think about others' mental lives. This latter problem is often traced back to a set of remarks in Wittgstein's Philosophical Investigations [1953, §243-315]. Details of this supposed problem needn't concern us here – see [Avramides 2001; Gomes 2011] for introductions to the problem – but some philosophers who address the conceptual problem take it that explaining our ability to think about others' mental lives requires us to take other people's mental lives to be perceptible. And this, they hold, supports the claim that our knowledge of others' mental lives is perceptual. (See [Malcolm 1958] for an influential presentation of this thought.) Let me turn now to inference. There have been two historically popular ways of cashing out the thought that our knowledge of others' minds is based on inference. According to analogical accounts, my beliefs about another's mental life are warranted in virtue of my recognising that my thoughts and feelings cause certain patterns of behaviour, perceiving other people exhibiting those same patterns of behaviour and concluding – by analogy – that when other people exhibit that behaviour, they also instantiate those thoughts and feelings [Mill 1865; Russell 1948]. According to best explanation accounts, my beliefs about another's mental 12 life are warranted in virtue of the hypothesis that the person instantiates those mental features being the best explanation of her observable behaviour [Pargetter 1984]. J.S. Mill is often claimed to have provided the paradigm statement of an analogical account. He writes: I conclude that other human beings have feelings like me, because, first, they have bodies like me, which I know, in my own case, to be the antecedent condition of feelings; and because, secondly, they exhibit the acts, and other outward signs, which in my own case I know by experience to be caused by feelings. [1865, p.190] This argument is typically presented as a case of enumerative induction. I observe that, in my own case, behaviour type B is caused by feeling type F; I conclude that for all humans, behaviour B is caused by feeling F; I observe another person exhibiting behaviour B and conclude that she instantiates feeling F. But so presented, it is vulnerable to the objection that observation of one positive instance is not sufficient to warrant belief in a universal statement. According to this objection, the argument from analogy no more justifies my believing that other people have thoughts and feelings than my having a mole under my left arm justifies my believing that everyone has a mole under their left arm [Malcolm 1958, p.969; Putnam 1975, pp.342-343]. There are two ways to respond to this objection. First, one might hold that enumerative induction from a single case is sometimes permissible. Hyslop and Jackson, for example, hold that enumerative induction from a single case is permissible when one already knows that the relation between the two features in question is causal [Hyslop and Jackson 1972, p.175]. Second, one might deny that the argument from analogy really proceeds from consideration of a single case. Ayer, for instance, holds that the analogical inference rests on a multitude of correlations between instances of mental properties and instances of behaviour, albeit instances all confined to a single person [Ayer 1956, 219-222]. Whatever the merits of these responses, the single-case objection is a poor objection to Mill whose discussion is much more sophisticated and interesting than typically presented. (See [Thomas 2001] for an excellent discussion of Mill's text.) Central to Mill's discussion – which bears 13 reading beyond the sample of text quoted above – is the thought that we are dealing with the class human beings. Human beings are members of a natural kind and Mill himself is a member of that kind. Since the laws of nature which govern our mental features apply to all members of the natural kind uniformly, Mill takes himself to be licenced in moving from the identification of those features of himself which hold in virtue of him being a member of that kind to the reasonable assumption that other members of the kind will instantiate the same features. This is comparable, Mill thinks, to the chemist who makes pronouncements about the properties of a new chemical element having conducted one proper experiment [Mill 1843, quoted in Thomas p.519]. Mill's positive proposal is closer to the best explanation accounts according to which our belief in others' mental states is justified in the same way as our belief in scientific unobservables: on the grounds that the postulation of such entities best explains the observed data. In the case of others' minds, the observed data is the movement of their bodies and the best explanation is the ascription to others of mental states. This is perhaps the dominant account of our knowledge of others' minds in the psychological literature, but it raises a number of questions. First, does inference to the best explanation warrant the beliefs of those who do not have explicit beliefs about the explanatory role of mental states – a group which I take to include most of us before we took up philosophy or psychology? Second, can it warrant the beliefs of children, say, who lack the conceptual resources to hold beliefs about the explanatory connections between mental states and observable behaviour? And finally, is the ascription of mental states genuinely the best explanation of other people's behaviour or are there other neuroscientific explanations which crowd it out? Two final comments on the perceptual and inferential approaches. First, it should be common ground that some of our knowledge of others' minds is inferential. We sometimes puzzle over another's strange behaviour, before concluding that it is explained by some fact about her mental life. This knowledge is based on inference. Or consider the way in which historians come to know what those in the past believed. Perhaps cultural historians of the British Empire know whether Dadabhai Naoroji – the first British Asian MP – regretted leaving mathematics for politics. But if they do so, it is because they have inferred it from historical evidence. The debate, then, should not be phrased as whether our knowledge of others' minds is either 14 perceptual or inferential, but given that some of it is inferential, whether it is all so. Second, in presenting the opposition between these accounts, I have taken it for granted that there is a distinction between perceptual and inferential knowledge. How are we to characterise this distinction? Defenders of a perceptual model sometimes seem to assume that a piece of knowledge is inferential if it is the result of a process of inferential reasoning [Cassam 2007a, p.160; cf. Price 1931, p.55]. But a piece of knowledge can be supported by inferential relations even if it is not the result of inferential reasoning [Brandom 2002, pp.95-98; Pryor 2004, p.190]. My belief that you're at home, for example, may come to me unbidden upon seeing your car in the driveway; in this sense, it is not the result of a process of inferential reasoning. But its epistemic justification may still lie in my warranted belief in an inferential relation between the proposition that your car is in the driveway and the proposition that you are at home. We need a fuller characterisation of the differences between perceptual and inferential knowledge if we are to confidently evaluate the reasons for thinking that one or other is the source of our knowledge of others' minds. 5. Next Steps I finish with some more general comments on scepticism about others' minds. As I've presented the issue, the aim is to identify the source of our knowledge of others' mental lives. The recent debate confines itself to discussion of perception and inference as possible sources of knowledge. This marks a change from the discussion conducted at the start of the previous century where other sources of knowledge, such as telepathy, were given serious consideration. Let me conclude by noting two ways in which broadening our horizons may help this debate. First, testimony. When one thinks about the way in which we come to know about others' mental lives, it is not perception or inference which stand out. Rather, other people tell us things – and amongst the things they tell us are facts about their mental life. Could testimony be a source of knowledge of others' mental lives? One might think not for a simple reason: knowledge gained through testimony presupposes that one knows that the other person has a mind, so it can't be used to explain how one gains such knowledge. (Stroud and Cassam raise this objection: [Stroud 1989, p.101; Cassam 2007a, p.157].) But this form of reasoning has a 15 parallel in discussions about perceptual knowledge: knowledge gained through perception presupposes that one knows that one is perceiving [Stroud 1996: pp.131-133]. And the presupposition claim about perception has been the subject of much discussion: it looks to lead to scepticism about perceptual knowledge and many have argued that it should be rejected [McDowell 1986, 1995]. It is worth considering whether the lessons of this debate can be applied to the case of gaining knowledge of others' minds through testimony and, if so, whether testimony could serve as a basic source of knowledge of others' minds [Gomes 2014]. Second, variety. I've assumed throughout that there is one way – or better, that there is some fundamental way – by which we come to know about others' minds. But perhaps this is false: perhaps there is no general way by which we come to know about the minds of others. Let us draw a distinction between two different ways of grouping known facts: on the basis that such knowledge has been gained from the same source, or on the basis that it all concerns the same domain. Call these two ways of classifying knowledge source-knowledge and domain-knowledge respectively. Some examples of source-knowledge include: the facts I know on the basis of perception; the facts that you know on the basis of reading Wikipedia; the facts which Priya knows through divine revelation. Some examples of domain-knowledge include: everything I know about cars; that which you know about Sri Lanka; the things you know about the Catholic Church. The difference between these two ways of classifying known facts is not always made clear, as when philosophers move interchangeably between discussing perceptual knowledge and knowledge of the external world. But we should be careful to mark the distinction for it need not be the case that some knowledge picked out via a certain domain has all arisen from the same source. And, indeed, although there are cases where all the things we know about a particular domain were gained from the same source – 'everything I learned about love I learned from romance novels' – this is the exception rather than the norm. Given that knowledge of others' thoughts and feelings is a type of knowledge picked out via its domain, we have no grounds for thinking that it is all gained via the same source. Does such variety have implication for the sceptical challenge? If the aim is to identify the means (perhaps plural) by which we know about others' minds, then we need some way of individuating sources of knowledge. 16 This is particularly important in a context in which psychological and neuroscientific investigation is providing us with a wealth of information on the mechanisms by which we ascribe mental states to one another [Nichols and Stich 2003]. There have been discussions of how to individuate sources of knowing in the epistemology literature [Nozick 1981, pp.179-185; Audi 2002; Cassam 2007b] but presentation of the problem of other minds often proceeds as if we have an unproblematic understanding of the means of knowing which are antecedently available for consideration. Addressing scepticism about others' minds may require renewing interest in this epistemological question.1 References Audi, R. (2002). The Sources of Knowledge. In P. Moser (ed.) The Oxford Handbook of Epistemology. Oxford: Oxford University Press. Austin, J.L. (1946). 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