Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 1 Sensitive knowledge: Locke on skepticism and sensation JENNIFER NAGEL, University of Toronto Anyone accustomed to thinking of external world skepticism as one of the core problems in philosophy is bound to be surprised by Locke's jaunty approach to this topic in the Essay Concerning Human Understanding. Is there a printed page before you now, or might you merely be dreaming that there is? Does anything exist beyond the idea of this page now in your mind, and can you infer with certainty the existence of 'any thing without [you], which corresponds to that Idea'? (4.2.14) When Locke describes this skeptical worry as 'that, whereof some Men think there may be a question made'(ibid.), it seems he does not take himself to be one of those men; indeed, he goes on to deride the skeptic and to say that 'no body can, in earnest, be so sceptical, as to be uncertain of the Existence of those Things which he sees and feels' (4.11.3). Nevertheless, Locke also provides a brief substantive answer to the skeptic's challenge, asserting that the senses really do inform us of the existence of outer objects. The label 'sensitive knowledge' is introduced to cover our grasp of the existence of the particular outer objects we encounter in experience. This choice of label in fact makes Locke a bold anti‐skeptic: in his system, knowledge, unlike mere judgment, entails certainty (4.14.4). Locke's introduction of sensitive knowledge is quite puzzling, however, not least because it seems to conflict with his general definition of knowledge, supplied just a few pages earlier. Knowledge was supposed to be 'nothing but the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas' Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 2 (4.1.2). Many critics of Locke have worried that restricting knowledge to relationships among ideas would bar knowledge from extending to the outer reality which 'corresponds to' these ideas. The question of how well Locke can answer such concerns leads us into a number of peculiar and intriguing passages on knowledge and the relationships between perception, reality, pain and pleasure. The present chapter aims to examine what Locke has to say about sensitive knowledge, to investigate several ways in which his remarks on this topic can be reconciled with what he says elsewhere, and to assess the merits of Locke's conception of sensitive knowledge both as a response to skepticism and as a part of the larger picture of human understanding painted in the Essay. Section 1: Definitions and distinctions Before examining the specifics of Locke's account of sensitive knowledge, some attention should be given to Locke's definition of knowledge as consisting in 'the perception of connexion and agreement, or disagreement and repugnancy' of ideas. (For ease of presentation 'connexion and agreement' will be abbreviated to 'agreement'; what holds for agreement with respect to positive claims generally also holds for disagreement with respect to the corresponding negative ones.) To begin, one might wonder what is meant by 'perception' in this particular context, whether the term is meant to register a merely subjective impression of a sort that might sometimes be mistaken, or a successful apprehension of objective fact. The Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 3 verb 'perceive' can now carry either the subjective sense of 'perceiving as' ('I initially perceived him as hostile towards me, but it turned out he was not'), or the objective sense of 'perceiving that' ('A good judge of character, she perceived that he was friendly'). In the former sense it is a contingent matter whether perceiving itself gets things right, although it might be the case that for certain kinds of objects – say, agreements of ideas – perceiving must succeed. On this subjective reading of 'perception' it would have to be something about the particular character of the objects of perception that explains why knowledge has the boundaries that it does: perhaps perception may be fallible, but perception of certain agreements of ideas – e.g. 'that white is not black' – must always hit the mark. Meanwhile, if we take the term 'perception' in the latter (objective) sense, perception itself is already a significant cognitive achievement: it is because what we are doing with those agreements of ideas is perceiving them that we count as knowers. When directed at a proposition, this objective sense of perceiving is classified by contemporary epistemologists as a factive attitude. The distinctive characteristic of factive attitudes is that they entail the truth of their complement clauses: a person can perceive that p only if p is true. Like 'perceives that,' mental state attitudes such as 'is aware that', 'sees that' and 'realizes that' are all factive attitudes; by contrast, 'judges that', 'hopes that' and 'doubts that' are not. It has been argued that all ascriptions of factive mental state attitudes require not only the truth of the complement proposition but also knowledge of this proposition on the part of the subject to whom the attitude is ascribed (Williamson 2000). If this view is right, Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 4 then a subject's perceiving that p already entails her knowing that p, for any proposition p; or in other words, perceiving that is itself simply a particular way of knowing that. There is some evidence from historical patterns of usage that Locke would have had the second (objective) sense of perceiving in mind: the Oxford English Dictionary cites many instances of this sense dating back as far as 1330, while the first citation of the subjective sense of 'perceiving as' is from 1884. More directly, Locke's own description of the contrast between knowledge and mere judgment makes it clear that his definition of knowledge must employ the objective or factive sense of perception. What distinguishes knowledge from judgment is whether an agreement of ideas is perceived or presumed, where presumption is fallible and perception a clear success term (4.14.4). Where we perceive such an agreement we have certainty and knowledge; where we presume it we lack certainty and have mere judgment. It might be objected that Locke's definition of knowledge speaks of perceiving an agreement of ideas rather than 'perceiving that' anything is the case; however, given Locke's understanding of the nature of propositions, perceiving an agreement of ideas actually is perceiving that a certain proposition is true, a point stressed by Ruth Mattern in her treatment of sensitive knowledge (Mattern 1978). Although various qualifications to Mattern's interpretation have been suggested (for example in Owen 2007, Rickless 2008), it is still widely agreed that in setting out his Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 5 definition of knowledge Locke is concerned with propositional knowledge rather than, say, knowledge by acquaintance. Locke maintains that knowledge 'all consists in Propositions' (2.33.19), or, in an even stronger formulation from the Stillingfleet correspondence: 'every thing which we either know or believe, is some Proposition' (1697c: 245). Now, if the sense of 'perception' employed in Locke's definition of knowledge is itself a special term for epistemic success with respect to a proposition, and especially if the sense of 'perceiving' in play already entails knowing, Locke's definition of knowledge as perception of the agreement of ideas is – for better or worse – not a reductive definition: it does not analyze knowledge into non‐epistemic constituents. One might then worry that no ground has actually been gained by defining knowledge in terms of this special notion of perception. If perceiving is itself already a form of knowing, then what the definition really does is just introduce a restriction on knowledge: there can be no knowledge beyond the particular kind of propositional knowledge that is constituted by the perception of agreement of ideas. The fact that Locke's definition does not explain but only restricts knowledge constitutes one reason to think that he meant his restriction of knowledge to agreements of ideas to be taken seriously. And while this definition may not do much to clarify the underlying nature of knowledge, it can still constitute a step forward in our understanding of knowledge if it is helpful to restrict and individuate the objects of knowledge or perception in the way that Locke does. Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 6 Locke's next move is exactly directed at identifying the objects of knowledge. In the passage immediately following the definition of knowledge as consisting in 'the perception of connexion and agreement, or disagreement and repugnancy' of ideas, Locke claims that the relevant agreement or disagreement falls into four types: (i) identity/diversity, (ii) relation, (iii) co‐existence or necessary connection, and (iv) real existence. Sensitive knowledge fits into this last category, although as we shall see shortly, not all knowledge of existence is sensitive knowledge – Locke thinks one can know of one's own existence intuitively, rather than sensitively, and of the existence of God through demonstration or proof. But from the division of knowledge into the four basic types, it seems Locke considers knowledge of existence to be something distinctive however it is attained. The fourth type of knowledge differs in several ways from the other three. Locke notes that the first three types of knowledge have something in common; in fact, he grants that the first and third members of the list could be subsumed under the second. Observing that identity/diversity and co‐existence or necessary connection 'are truly nothing but Relations' (4.1.7), Locke maintains that the distinctive character of these particular relations still earns them special separate mention. The last member of Locke's list of types of knowledge, knowledge of 'real existence', then stands out as something of a different sort altogether, something Locke chooses not to characterize here as the perception of some further kind of relation. Within Locke's general framework, it is certainly possible to describe knowledge of real existence as involving the apprehension of a relation between ideas; indeed, we Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 7 shall see that Locke draws attention to this point when discussing sensitive knowledge in later work. However, in his primary description of our knowledge of the existence of things in the Essay, Locke does not speak directly of agreement between ideas: this type of knowledge is of 'actual real Existence agreeing to any Idea' (4.1.7). Locke's choice of the emphatic 'actual real' modifying 'existence' seems to suggest that something more than the mere idea of existence is perceived to figure in the agreement here. Even if relations of ideas are in fact perceived when experience yields knowledge of the existence of objects, here Locke seems to want to stress the extent to which this sort of knowledge involves being oriented towards things in the world as well as ideas in the mind. One radical proposal for reconciling knowledge of existence with the definition of knowledge as perception of the agreement of ideas should be mentioned at this juncture. John Yolton observes that talk of an 'agreement of ideas' might be ambiguous. Of course ideas must be involved in an agreement of ideas, but perhaps Locke thought the agreement in question was not always between ideas and other ideas; Yolton suggests that we may sometimes perceive agreements between ideas and an extra‐mental reality (1970: 110‐1). Such a proposal would make it unproblematic for Locke to speak of knowledge of 'actual, real Existence' agreeing to an idea. However, as a number of commentators have pointed out, there are many textual passages in the Essay that cut directly against such a view, starting quite conspicuously with the heading of the section in which the official definition appears: 'Knowledge is the Perception of the Agreement or Disagreement of two Ideas' Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 8 (4.1.2). Detailed textual arguments against the Yolton proposal have been presented in a number of places (see especially Mattern 1978, Soles 1985 and Newman 2004). Unless one is prepared to disregard a very considerable body of textual evidence, one cannot reconcile Locke's remarks on knowledge of existence with his definition of knowledge by broadening the notion of agreement in this manner. Having divided knowledge into four sorts, Locke's next move is to distinguish three degrees of knowledge, having different levels of certainty on account of the 'different way of Perception' involved in each. Intuitive knowledge is 'the clearest, and most certain' type of knowledge we can have: it consists in the perception of 'the Agreement or Disagreement of two Ideas immediately by themselves, without the intervention of any other' (4.2.1). Our knowledge that white is not black or that three is greater than two requires no reasoning or effort once the relevant ideas are in view; it 'forces it self to be immediately perceived', and is psychologically compelling or 'irresistible', excluding the possibility of doubt (ibid.). Locke maintains that our grasp of our own existence is a particularly strong case of intuitive knowledge, registered inescapably at every turn. According to Locke we have an 'internal infallible Perception that we are', because 'in every Act of Sensation, Reasoning, or Thinking, we are conscious to our selves of our own Being; and, in this Matter, come not short of the highest degree of Certainty.' (4.10.3) Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 9 Moving down the scale to the next degree of knowledge, demonstrative knowledge, the mind perceives the agreement or disagreement between ideas only by means of a proof, or a series of rational steps, each of which is intuitive in character. Requiring 'pains and attention' (4.2.4), this type of knowledge can extend to propositions we are psychologically capable of doubting (4.2.5), and although a successful demonstration will remove this doubt, it does not provide quite the same level of certainty or clarity as intuitive knowledge. One reason for the lower degree of certainty is given at 4.2.7: particularly in the course of a long proof, it is possible for us to omit a step or miscalculate, and at the end embrace an incorrect result, thinking we have demonstrative knowledge where we do not. Bad attempts at demonstration can remove doubts where these doubts should have been retained. Intuitive knowledge, by contrast, concerns what could never have been doubted in the first place, and is self‐certifying, in that it is not possible to be mistaken about whether one knows something intuitively. Even to entertain an agreement of ideas that is intuitively knowable is already to know it intuitively. Intuition and demonstration are two of the three 'degrees' of knowledge Locke identifies; the third is sensitive knowledge. The passage in which sensitive knowledge is first introduced reads like a postscript to the main story about intuition and demonstration: These two, (viz.) Intuition and Demonstration, are the degrees of our Knowledge; whatever comes short of one of these, with what assurance soever embraced, is but Faith, or Opinion, but not Knowledge, at least in all general Truths. There is, indeed, another Perception of the Mind, employ'd about the particular existence of finite Beings without us; which going beyond Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 10 bare probability, and yet not reaching perfectly to either of the foregoing degrees of certainty, passes under the name of Knowledge. (4.2.14) The claim that this perception of the mind just 'passes under the name of Knowledge' might suggest that for Locke sensitive knowledge is not in fact a form of knowledge, strictly speaking. In this spirit Samuel Rickless maintains that 'what Locke honorifically calls "sensitive knowledge"' is not really a form of knowledge at all, but rather 'a kind of less‐than‐certain judgment-what Locke calls "assurance"- founded in the highest degree of probability' (2008: 85). Such an interpretation makes it easier to reconcile Locke's claims about sensitive knowledge with the evident fallibility of our judgments of external existence. However, the Rickless proposal also carries certain costs. Seeing sensitive knowledge as really a form of less‐than‐certain judgment will oblige us to explain why Locke does not overtly classify our grasp of the existence of outer things as a kind of probable judgment from the start, and to explain away various passages in which Locke does describe this awareness of outer things as involving certainty. Rickless contends that Locke is loose on these points because the degree of probability in judgments founded on present sensation is high enough to approximate knowledge for practical purposes. However, there are some reasons to resist the suggestion that Locke is deliberately blurring the line between knowledge and mere judgment: from the first chapter of the Essay he states that an aim of the book is 'to search out the Bounds between Opinion and Knowledge' (1.1.3), and we are reminded of the significance of this distinction at the start of the later Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 11 discussions of knowledge (4.1.2) and judgment (4.14.1). One might also question Rickless's claim that Locke always uses the term 'assurance' to designate less‐than‐ certain judgment grounded in high probability. David Owen has suggested that Locke sometimes uses 'assurance' as an umbrella term covering both knowledge and judgment (Owen, MS). To complicate matters, there are also passages in the Essay where 'assurance' seems to denote the feeling of subjective confidence that may accompany various types of opinion (1.1.2), action (1.3.13), faith (4.16.14) and knowledge (4.3.3). One such passage appears in Locke's discussion of the epistemic status of apparent divine revelation. Locke contends that what really matters is knowing that one's impressions came from God as opposed to some other source, adding that, "If I know not this, how great soever the Assurance is, that I am possess'd with, it is groundless." (4.19.10) In the following discussion, Locke is clear that assurance might be produced in various more or less rational ways, by sources ranging from the warmth of enthusiasm to the probability of a proposition, or even to the self‐evident truth of a proposition. If assurance can be generated in this last manner it clearly does not exclude knowledge: recognition of the self‐evident truth of a proposition would produce not highly probable opinion but knowledge in the highest degree. It is possible that Locke may be shifting between various technical and non‐technical meanings of 'assurance' in the Essay, but any such shifts would make it harder to defend Rickless's claim that Locke's claims about assurance provide uncontroversial evidence that he meant to exclude sensitive knowledge from counting as knowledge, strictly speaking. Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 12 As another possible reservation about the Rickless proposal, those critics of Locke who were concerned about the mediation of ideas in our grasp of outer existence will still be unsatisfied if Locke is read as maintaining that experience gives us highly probable judgment of the existence of outer things. Like knowledge, judgment for Locke also invariably involves a cognitive relation to ideas rather than bare outer objects or real existence; the distinctive feature of judgment is just that the agreement of ideas is presumed, rather than perceived (4.14.4). Lastly, the confrontation with the skeptic about the external world is not going to be settled simply by softening the claim that we know external objects exist into the claim that we are highly justified in believing that external objects exist. Many skeptics will be equally happy to challenge our claims to justification. Sextus Empiricus, for example, took pains to develop many arguments against the Academic skeptics who gave up claims to knowledge but sought to substitute softer claims about what is probable or persuasive; according to Sextus's Pyrrhonian skepticism we lack not only knowledge but also rational grounds to find any impression more probable or credible than any other (Sextus Empiricus 1985, 1.33; cf. Wright 1991). Given both the costs of demoting sensitive knowledge to the status of judgment and the problems left unsolved by this approach, it may be worth attempting to find a way of construing sensitive knowledge as a kind of knowledge, strictly speaking. Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 13 2. The nature of sensitive knowledge There are two passages in the Essay in which Locke describes sensitive knowledge in some detail, both of which begin with a description of the skeptical problem. In the chapter on degrees of knowledge Locke writes: There can be nothing more certain, than that the Idea we receive from an external Object is in our Minds; this is intuitive knowledge. But whether there be any thing more than barely that Idea in our Minds, whether we can thence certainly inferr the existence of any thing without us, which corresponds to that Idea, is that, whereof some Men think there may be a question made, because Men may have such Ideas in their Minds, when no such Thing exists, no such Object affects their Senses. (4.2.14) Whatever reluctance Locke shows towards accepting the legitimacy of the skeptic's worries, the problem is not that the skeptic has introduced a separation between the occurrence of an idea and the existence of an outer thing; in a later chapter devoted to sensitive knowledge Locke again countenances the possibility of this separation, but in his own voice, and more vividly: For the having the Idea of any thing in our Mind, no more proves the Existence of that Thing, than the picture of a Man evidences his being in the World, or the Visions of a Dream make thereby a True History. (4.11.1) In both places Locke's subsequent response to the skeptic exploits the difference between merely having or entertaining an idea in one's mind and actually receiving that idea through sensation. So at 4.11.2, Locke claims that it is not simply having an idea in mind but rather 'the actual receiving of Ideas from without, that gives us notice of the Existence of other Things, and makes us know, that something doth exist at that time without us, which causes that Idea in us, though perhaps we neither know nor consider how it does it.' Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 14 That last remark may at first appear to convey what a contemporary epistemologist would call an 'externalist' outlook, where externalism counts the third‐person perspective as decisive in ascriptions of knowledge. If I in fact receive ideas from an outer world in sensation, and form beliefs about the world accordingly, the externalist can count me as having knowledge of outer things in virtue of the causal origin of these ideas, however little I as a subject may know about the processes by which these sensations were produced in me. In strong forms of externalism about perceptual knowledge the subject need not even recognize that she is having sensations in order to gain knowledge from the world; what matters is just that reliably true beliefs about the world be produced by these sensations. Some commentators are inclined to read Locke as espousing an externalist view of perceptual knowledge. Martha Bolton, for example, sees Locke as committed to a 'roughly reliabilist' view of warrant, in which ideas 'represent only by virtue of their causal origin' (2004: 301). On this reading, Locke seeks no rational basis for dispelling the skeptic's worries: the reliability of 'our faculties, operating properly in their natural setting,' is according to Bolton simply 'taken for granted' in the context of Locke's main discussion of perceptual warrant, although elsewhere supported with an argument which invokes the benevolence of God (2004: 305). However, if Locke is an externalist about perception, he is not a straightforward one. As Bolton herself acknowledges, Locke also draws attention to the perspective of the subject in the context of his answer to the skeptic. It is not just the bare fact that he Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 15 is enjoying 'the actual receiving of Ideas from without' that justifies the subject in his claims about outer objects; apparently the subject also gains some kind of warrant or evidence for these claims in his awareness that he is receiving ideas of objects in this manner, rather than say, conjuring up those ideas through memory or imagination. However, it is a live question whether Locke succeeds in showing how the subject's perspective on the character of his mental activity could contribute to his warrant; Bolton thinks not, but one might attempt to dispute that finding on Locke's behalf. A review of the relevant passages is in order. When Locke grants that we may fail to consider the exact workings of the 'actual receiving' of ideas, he does not mean that the knowing subject could be unaware of the fact that he is having sensation: his point there is not that the self‐conscious perspective is unimportant but that the specific details of the processes underpinning sensation do not have to be understood by the subject. Responding to the skeptical worry, he says: But yet here, I think, we are provided with an Evidence, that puts us past doubting: For I ask any one, Whether he be not invincibly conscious to himself of a different Perception, when he looks on the Sun by day, and thinks on it by night; when he actually tastes Wormwood, or smells a Rose, or only thinks on that Savour, or Odour? We as plainly find the difference there is between any Idea revived in our Minds by our own Memory, and actually coming into our Minds by our Senses, as we do between any two distinct Ideas. (4.2.14) Just as the existence of the self is known at every waking moment (in the 'internal infallible Perception that we are'), so Locke claims here that the character of our present mode of thought, whether sensation or recollection, is always available to Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 16 us: we are 'invincibly conscious' of the way in which any given idea is presenting itself to us, as well as the content of the idea presented. Earlier in the Essay Locke had advanced the milder claim that 'the operations of our minds, will not let us be without, at least some obscure Notions of them' (2.1.25); it now seems that even these obscure notions must always be distinct enough that there is no risk of our mistaking recollection for sensation. The perception one enjoys when seeing the sun is different from the perception involved in recollecting it, not in virtue of any of the sensible qualities the sun is represented as having, but in virtue of one's awareness of the character of one's own current mode of thought, of the operations of one's mind. The operations of one's mind generate what Locke calls ideas of reflection; the difference between the ideas of reflection generated in sensation and recollection constitutes evidence the subject cannot fail to notice. Locke is emphatic on this point, claiming in the later chapter elaborating the concept of sensitive knowledge that 'there is no body who doth not perceive the difference in himself, between contemplating the Sun, as he hath the Idea of it in his Memory, and actually looking upon it' (4.11.5). This perceptible difference is then supposed to give the subject 'certain knowledge, that they are not both Memory, or the Actions of his Mind, and Fancies only within him; but that actual seeing hath a Cause without' (ibid.). Locke seems to think that the skeptic has made the mistake of underestimating what is available to consciousness, failing to notice that we are aware not only of the sensible qualities of outer objects – say, the brightness and warmth of the sun – but Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 17 also of the manner in which these ideas are being presented to us. Consciousness involves having ideas of the ways in which our minds are affected by (or how our minds affect or produce) these ideas of objects, although we might not often have occasion to attend self‐consciously to those ideas of our modes of thought, any more than we have occasion to attend self‐consciously to the idea of the existence of the self which is also supposed to be present 'in every Act of Sensation, Reasoning, or Thinking'. A conscious person is not simply struck by a bare idea of an object, say a rose; a conscious person will feel that he is presently seeing the rose, or remembering it, or deliberately visualizing it. The same idea of a rose is present whether the rose is now recollected or sensed; but a further idea of the mind's current mode of operation – an idea of reflection – is also present to consciousness. If these ideas of reflection can be taken at face value, a person can tell whether his occurrent idea of the rose does or does not indicate the existence of a real rose before him now. It is worth mentioning at this point that in drawing attention to the distinction between sensation and recollection Locke does not mean to imply that memory never yields knowledge of existence. In fact his discussion of memory extends the scope of sensitive knowledge beyond what is immediately present to us in sensation: in his more detailed treatment of the topic he contends that memory of past perception yields sensitive knowledge of the past existence of the object, of its existence at the time it was sensed (4.11.11). Recollection of a past experience feels different from recollection of a past episode of imagining, and different again from Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 18 current imagination or sensation. Something about the character of recollection of past experience, like something about the character of present sensation, is supposed to yield some warrant or evidence for our claims about the past existence of outer objects, just as the special felt character of current sensation yields warrant for claims about the present existence of what we are sensing. Locke is not alone in thinking that the way our experiences feel to us – what James Gibson calls 'the peculiar tang of reality' (1917: 174) – is itself a source of warrant for beliefs about the world. This very notion continues to circulate in contemporary epistemology. So James Pryor, for example, argues that sensations and memories of sensations can justify beliefs about the world because of the way it feels to have them: when we see or remember what we have seen we enjoy a special 'feeling of seeming to ascertain that a given proposition is true.' (2004: 357) This feeling, which Locke would classify as a feature of certain ideas of reflection, is not always a feature of conscious representation: like Locke, Pryor notes that it is also present in memory but absent in daydreaming and visualization. Empirically, philosophers such as Locke and Pryor are on solid ground in claiming that a conscious person will always have some idea of his mode of cognition as well as the object of his thought. Contemporary empirical researchers agree that consciousness does not present us with information that is undifferentiated as to source, and for good reason: as the psychologist Marcia Johnson puts it, 'it seems unlikely that a cognitive system would be viable if all information from all sources Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 19 were simply represented in a jumble of amodal, abstract, propositional statements with no clue at all as to their origin' (1998: 181‐2). The contemporary psychologist shows broad agreement with Locke in saying that 'the cognitive system represents information in ways that preserve its history' (1988: 181); Johnson dubs this capacity 'source monitoring' and argues that it is an integral part of our conscious experience. However clear it is that Locke has succeeded in identifying a genuine feature of our conscious mental lives, this appeal to our mental representations of information source does not seem terrifically compelling as an initial response to skepticism (although, as we shall see in the next section, Locke does have a further move to make). If the skeptic is wondering whether any of our ideas match outer reality, it will be little further effort for him to wonder whether our ideas of the present workings of our mind are trustworthy. Perhaps we only feel that we are sensing, when in fact we are dreaming or subject to the machinations of an evil genius. We do not even need to contemplate outlandish scenarios to find difficulties here: everyday experiences of source confusion are not hard to find. A ringing in my ears might be mistaken for the sound of an outer bell, or I might feel I remember what I only imagine having experienced. Psychologists who examine source monitoring are agreed that this capacity is fallible. So, despite her emphasis on the importance of source monitoring capacities, what Johnson says about the reliability of these capacities is not that they provide us with infallible evidence, but rather – more modestly – that through these capacities we are 'able to make better than chance Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 20 attributions about the epistemological status of our mental experiences' (1998: 181). If our grasp of our present mode of cognition is known to be fallible, the skeptic will urge, then in any given case we have some reason for doubt, and must fall short of the certainty Locke requires of knowledge. If Locke is overlooking the possibility of erroneous ideas of our present mode of thought, this is consistent with a general carelessness on his part about the problem of error. For example, it is often noted that Locke pays very little heed to the problem of perceptual errors involving simple ideas, such as the misperception of a distant square tower as round, and that he would face great difficulty explaining such cases in light of his view that simple ideas – like ideas of shape, for example – are invariably real and true (2.30.2). Doubts about simple ideas of sensation are generally supposed to be assuaged by the observation that sensation is a passive process; presumably Locke would also want to draw attention to the fact that reflection is passive as well (2.1.25). On the side of sensation, it has been argued that passivity does not support a fully satisfactory response to the problem of error (Bolton 2004, LoLordo 2008); one might reasonably have similar worries concerning reflection. One way of understanding Locke's failure to be concerned with the possibility of occasional error about current cognitive mode is to read him as having a rather modest goal at this point in the argument: perhaps his aim is not yet to show why the skeptic's doubts are unreasonable, but rather to explain why they do not Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 21 ordinarily affect us in practice. When Locke claims that in our consciousness of our present mode of cognition 'we are provided with an Evidence, that puts us past doubting', perhaps he wants to present the reasons why as a matter of fact we do not suffer from skeptical doubts in ordinary life. Our ordinary consciousness of ideas as originating from some particular source – memory, visualization, present experience – is what ordinarily bars us from suffering doubts about the outer existence of sensed objects as we are sensing them. Doubts are not inconceivable in principle, but unlikely in practice. Perhaps the task of establishing that these doubts are unreasonable has yet to be undertaken at this point in the text. We recall from the discussion of the fallibility of demonstrative reasoning that Locke allows that sometimes doubts can be removed where they should have been retained; the skeptic might be happy to grant that our ordinary sense of our cognitive activity tends to remove doubts about the existence of outer objects without thereby granting that these doubts ought to have been removed in this manner. In order to credit Locke with an argument that skeptical doubts are unfounded, or, equivalently, that our sense of our own cognitive activity gives us good grounds to accept the apparent testimony of the senses, as opposed to merely compelling us psychologically to accept this testimony, we need to examine more closely what he has to say about the content of our ideas of our own cognitive activity, and the circumstances under which these ideas are activated. How exactly is the idea of present sensation different from the idea of visualization or recollection? And how can we be assured that it is activated appropriately? Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 22 Locke is unequivocal that we have a firm grip on the differences between the various modes of thought. We have seen that he considers the distinctions here to be as sharp as any we can draw: 'We as plainly find the difference there is between any Idea revived in our Minds by our own Memory, and actually coming into our Minds by our Senses, as we do between any two distinct Ideas.' (4.2.14) Indeed a particularly strong claim about the strength of our understanding of our modes of thought appears in the second reply to Stillingfleet, in response to a worry about 'a want of connexion between our Ideas and the things themselves'. Here Locke is explicitly concerned to defend the conformity of sensitive knowledge to his general definition of knowledge as the perception of agreement of ideas. Although the passage is somewhat controversial (scholars from Yolton to Rickless have been concerned that it may represent a shift from the position espoused in the Essay), it bears on all our main themes and is worth quoting at length: In the last place your Lordship argues, that because I say, That the Idea in the Mind proves not the Existence of that thing whereof it is an Idea; therefore we cannot know the actual Existence of any thing by our Senses; because we know nothing, but by the perceived Agreement of Ideas. But if you had been pleased to have consider'd my Answer there to the Scepticks ... you would, I humbly conceive, have found, that you mistake one thing for another, viz. The Idea that has by a former Sensation been lodged in the Mind, for actually receiving any Idea, i.e. actual Sensation, which I think I need not go about to prove, are two distinct things, after what you have here quoted out of my Book. Now the two Ideas, that in this Case are perceived to agree, and do thereby produce Knowledge, are the Idea of actual Sensation (which is an Action whereof I have a clear and distinct Idea) and the Idea of actual Existence of something without me that causes that Sensation. (1697c: 249‐ 50) Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 23 Here we see again the appeal to consciousness of one's mode of thought as a line of defense against skepticism, now enriched with the claim that the idea of actual sensation is itself a clear and distinct idea. It is worth resolving a potential ambiguity in the expression 'idea of actual sensation' here. Taking the 'of' to indicate origin, one might read the 'idea of actual sensation' as an idea – say, of a rose – whose source is current sensation and whose content is whatever is sensed. On the other hand, taking the 'of' to indicate representational content, one might take 'idea of actual sensation' to be an idea whose content is the mode of thought we call sensation, an idea of the particular mode of cognition in which experiences are produced by outer objects. Here Locke's meaning is clearly the second: it is the mode of thought that counts as 'an Action,' and if Locke's reply is to meet Stillingfleet's objection on this point it has to be the idea of 'actually receiving any Idea' that is what Stillingfleet failed to consider. After Locke glosses 'actually receiving any Idea' as 'actual Sensation', the subsequent more explicit formulation makes it clear that Locke means to refer to 'the Idea of actual Sensation'. The idea of actually receiving any idea is – given its generality – not an idea of something like a rose presented in a special manner; the idea of actually receiving any idea is an idea of a general manner in which the subject is affected, an idea of reflection. Now, if Locke is claiming that the process of sensation gives us an idea of the cognitive mode of sensation as well as an idea of what is sensed, this much is entirely consistent with his position in the Essay. In the chapter on modes of thinking Locke says that being appropriately affected by external objects 'furnishes the mind with a Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 24 distinct Idea, which we call Sensation; which is, as it were, the actual entrance of any Idea into the Understanding by the Senses.' (2.19.1) It is not hard to see how the general idea of actual sensation, understood this way, is perceived to agree with the idea of the existence of an external cause: a vital element in taking oneself to be having a sensation as opposed to, say, a mere daydream, is taking oneself to be affected by a really existing external cause (cf. Newman 2007: 342). Locke himself explains our grasp of the relationship between the idea of sensation and the idea of an external cause as follows: For though when my Eyes are shut, or Windows fast, I can at Pleasure recall to my Mind the Ideas of Light, or the Sun, which former Sensations had lodg'd in my Memory; so I can at pleasure lay by that Idea, and take into my view that of the smell of a Rose, or taste of Sugar. But if I turn my Eyes at noon towards the Sun, I cannot avoid the Ideas which the Light, or Sun, then produces in me. So that there is a manifest difference between the Ideas laid up in my Memory; (over which, if they were there only, I should have constantly the same power to dispose of them, and lay them by at pleasure) and those which force themselves upon me, and I cannot avoid having. And therefore it must needs be some exteriour cause, and the brisk acting of some Objects without me, whose efficacy I cannot resist, that produces those Ideas in my Mind, whether I will, or no. (4.11.5) We sense our own power over the ideas conjured in daydreaming, and our own lack of power over the ideas actually received in sensation: the 'Action whereof I have a clear and distinct idea' in sensation is an action which involves the production of ideas in my mind which 'I cannot avoid having', and our lack of control over the ideas of sensation is something we learn empirically, or so this passage suggests. It is then integral to our conception of this mode of thought that the relevant experiences are produced by some really existing outer object. Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 25 On the present understanding of sensitive knowledge, in veridical experience of a rose one is aware of the same idea of the rose that is present in memory or imagination, and one is furthermore aware of oneself as sensing rather than remembering or imagining; that is, one has an 'Idea of actual Sensation,' where this latter reflective idea of one's current mode of thinking represents the real existence of an external cause. There is nothing in the idea of the object alone – the rose in this case – that itself points to real existence. Knowledge of the existence of the rose is not like the intuitive knowledge one has of one's own existence, in which any contemplation of the idea of the self obliges us to recognize the self as existing. Furthermore, the connection between the idea of the rose and the idea of an outer cause is not made by a sequence of rational steps; this is not like the demonstrative reasoning that is supposed to lead us from the idea of God through considerations of the cause of being to a recognition that God must exist. There is nothing in the idea of the rose itself from which one might deduce through a series of steps that the rose is actual rather than imagined. The connection between the idea of the rose and the idea of existence is made rather only through their simultaneous presentation to the mind, with the latter idea coming into play as part of one's reflective idea of sensation. If Locke were a straightforward externalist, he could allow that sensitive knowledge is founded directly on the 'actual entrance' of ideas from external objects; what he says instead is that we know particular external objects exist 'by that perception and Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 26 Consciousness we have of the actual entrance of Ideas from them.' (4.2.14) What makes knowledge of ordinary external things possible is not just sensation but consciousness of sensation as such: it matters that we are conscious not only of the idea of the rose, but also of the 'actual entrance' of this idea. Because there is a perceived agreement of ideas here – an agreement between the reflective idea of sensation and the idea of the real existence of an outer cause – sensitive knowledge counts as a form of knowledge; because the connection between the central content presented to one's mind (in this case, the idea of the rose) and one's idea of one's mode of thought (in this case, the idea of actual sensation) is not intuitive agreement but mere temporal coincidence, sensitive knowledge yields a lower degree of certainty than intuition or demonstration. On this view, we know that the things we sense exist because as we sense them we are – and feel ourselves to be – in a mode of thought that is known to be directed at outer objects. Sensitive knowledge is enabled by the joint functioning of sensation and reflection. A number of objections could be brought against this type of view. One is the classic 'binding problem': it is not clear how Locke would account for a situation in which I am presently sensing a rose while remembering a daffodil (or worse, while remembering the same rose, as seen earlier this day). But the problem of how groups of ideas are bound together is a quite general problem within Locke's system, not something particular to the problem of sensitive knowledge, and this is not the place to explore the question of whether or not the resources available to him are sufficient to address it. Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 27 Another problem concerns the activation of the idea of sensation. It might seem that the modal idea of what I can or cannot do with a given idea somehow has to make a manifest difference in a single moment of perception. But Locke is not saying that I will take myself to be sensing rather than merely imagining the sun only after I attempt to dispel the idea of light and discover I cannot; he thinks that one is invincibly conscious of the mode of one's perception at every moment. Fleshing out Locke's position, it must be that the reflective idea of a mode of thought – say, of sensation – could now be represented to the subject in an instant even if that complex idea originally took time and pains to acquire. Perhaps the very young child will need to experiment with her control over her ideas; once we have acquired the appropriate ideas of our modes of thought these distinctions may be represented in a flash, at least in a rudimentary way. Presumably an adult with the appropriate track record of reflection can see herself as powerless over an idea (or as the result of 'the brisk acting of some Objects without me') without running through a test of her powers over the idea. It is a consequence of the view suggested here that very young children with no ideas of reflection whatsoever will not have sensitive knowledge; to the extent that very small children are poor judges of the distinction between reality and fantasy this might not be an unwelcome result. In any event, even if Locke is ready to claim in the correspondence with Stillingfleet that he has a clear and distinct idea of the action of sensation, it does not follow that appreciation of such a clear and distinct idea – which would presumably require self‐conscious attention to one's mode of thought – must be involved in every Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 28 moment of sensitive knowledge. As long as one's awareness of oneself as sensing includes at least the minimal appreciation of sensation as involving the impact of an outer cause, one can have knowledge of the existence of the things one is sensing. Recalling Locke's claim that 'the Operations of our minds, will not let us be without, at least some obscure Notions of them' (2.1.25), as long as the obscure notion of sensation includes the idea of an outer cause, sensitive knowledge should remain possible. It would be good to have an account of exactly what activates the idea of sensation rather than the idea of some other mode of thought at any instant, if it cannot always be the temporally extended exercise of flexing my power over my current ideas. Perhaps sensation is somehow a default mode for me, whose ordinary force is quelled when awareness of my own efforts to visualize or recollect naturally dispels the idea of sensation; perhaps awareness that I am, say, attempting to recall something will naturally prime me to understand what comes then to mind as recalled rather than presently sensed. Or perhaps perceptible factors such as richer phenomenal detail play a part in inclining us to believe that we are presently sensing rather than recollecting or visualizing. Some further details concerning the activation of the idea of sensation could aid Locke in establishing that recognition of sensation as such yields warrant for our claims about the world, rather than just happening to dispel doubts as a matter of psychological fact. However, the basis of our taking ourselves to be in one mode of thought rather than another is even now considered a difficult problem in cognitive psychology; Locke cannot be faulted for Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 29 supplying us with only some fragments of the solution to this subtle empirical question. There is a further problem with the suggestion that skepticism can be defused by recognition that the idea of sensation incorporates the idea of an external cause: appeal to external causes is much too generic to satisfy the skeptic. The skeptic typically does not press us on whether sensation can be distinguished from active modes of thought such as recollection and visualization; the skeptic typically worries about distinguishing sensation from other passive modes of thought, modes such as hallucination and dreaming. Noticing that I am powerless over an idea does not establish that the idea is the product of a resembling cause rather than a dream or evil demon. Of course, in insisting that the idea of sensation incorporates the idea of an external cause Locke is not saying that the idea of sensation has nothing more to it than that notion of passivity; there may be other features of this mode of cognition that further distinguish it from states such as hallucination or dreaming, and perhaps at least some of these features are evident to us even when we have only an 'obscure notion' rather than a clear and distinct idea of our present mode of thought. But close attention to these other passive modes raises the obvious worry that in these modes one of the many things we are confused about is our current mode of thought: we take ourselves to be sensing things when we are not. There are two distinct problems here. The milder problem concerns the possibility of occasional errors concerning one's present mental state, considered in a context Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 30 in which most of one's mental state evaluations are assumed to be accurate. The objection is that if occasional failure is possible, one ought to doubt in any instance whether one has succeeded. Notice that a parallel problem could be raised with respect to demonstrative reasoning: if we occasionally go wrong in a proof, perhaps we ought always to worry that we have failed to reason correctly in the present instance. However, one might respond on Locke's behalf that the demand that we not only connect our ideas correctly but also know that we have done so is a demand for second‐order rather than first‐order knowledge. Knowing that one has reasoned correctly (or even dwelling on the nature of one's reasoning) is not obviously a requirement for knowing the solution to a mathematical problem. Knowing that I know that there is a rose in front of me at the present moment might require higher‐order reflection on the accuracy of my current self‐ascription of mental state, but just knowing that there is a rose there need not. In any event, the claim that knowing always requires knowing that one knows promises to launch a vicious regress, and is for that reason an undesirable feature of any epistemological theory (for more argument on this point, see Williamson 2000). The harder problem involves a more radical skepticism, in which one worries not about occasional failures taken against a background of success, but about according any legitimacy at all to our supposed capacity to distinguish modes of thought. Perhaps we are lodged in some extended dream and only feel that we are sometimes sensing and sometimes imagining. Locke expresses doubts that this form of skepticism is really psychologically possible for us, but grants that someone might Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 31 'be resolved to appear so sceptical, as to maintain, that what I call being actually in the Fire, is nothing but a Dream' (4.2.14). To respond to this deeper skeptical challenge, Locke changes his tactics. 3. Pleasure, pain, and certainty 'as great as our Happiness, or Misery' Locke's first answer to the more radical form of skepticism runs as follows: That we certainly finding, that Pleasure or Pain follows upon the application of certain Objects to us, whose Existence we perceive, or dream that we perceive, by our Senses, this certainty is as great as our Happiness, or Misery, beyond which, we have no concernment to know, or to be. (4.2.14) In the more detailed treatment of sensitive knowledge in chapter 11, Locke appeals again to pain and pleasure in response to the hypothetical radical skeptic: As to my self, I think GOD has given me assurance enough of the Existence of Things without me: since by their different application, I can produce in my self both Pleasure and Pain, which is one great Concernment of my present state. (4.11.3) Later in the same chapter, in response to the skeptic who says that all our experiences are nothing more than 'the series and deluding appearances of one long Dream, whereof there is no reality', Locke jovially remarks that the skeptic 'may dream that I make him this answer': That the certainty of Things existing in rerum Naturâ, when we have the testimony of our Senses for it, is not only as great as our frame can attain to, but as our Condition needs. For our Faculties being suited not to the full extent of Being, nor to a perfect, clear, comprehensive Knowledge of things free from all doubt and scruple; but to the preservation of us, in whom they are; and accommodated to the use of Life: they serve to our purpose well enough, if they will but give us certain notice of those Things, which are convenient or inconvenient to us. (...) So that this Evidence is as great, as we can desire, being as certain to us, as our Pleasure or Pain; i.e. Happiness or Misery; beyond which we have no concernment, either of Knowing or Being. Such an assurance of the Existence of Things without us, is sufficient to direct Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 32 us in the attaining the Good and avoiding the Evil, which is caused by them, which is the important concernment we have of being made acquainted with them. (4.11.8) These passages are surprising in two ways. The first surprise is that Locke is suddenly willing to engage the skeptic on the skeptic's own terms: in characterizing the objects we think we sense to be things that we either 'perceive, or dream that we perceive, by our Senses,' Locke indicates a willingness to suspend his ordinary assumptions about the reliability of our capacity to discriminate our current mode of thought. The second surprise is the identification of a special relationship between the evidence for the existence of an object and the pleasure or pain it can produce in us. Locke's claims on the latter point might at first seem to depend on some empirical confusion: surely one can experience pleasure or distress while dreaming, without later seeing this as any reason to take the apparent objects of one's dreams to be real. However, Locke does not say that pleasure or pain is invariably a direct sign of the existence of an object. An idea that happens to have been accompanied by pleasure or pain need not be the idea of a really existing object: what matters is our 'certainly finding' pleasure or pain to 'follow upon' our encounters with an object. Not to beg any questions about the reality of the objects being encountered, we would need to construe these encounters from the subject's perspective, say, as constituted by the experience of suitably related ideas. We gain assurance that some set of ideas originates in something that exists if pain and pleasure are reliably Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 33 found to follow upon this set of ideas – it is not enough that some random occurrence of this set of ideas should happen to have sparked pleasure or pain. When we look back on a dream we no longer expect its objects to serve as reliable sources of future pleasure or pain, and can safely dismiss them as unreal. One can of course deliberately and reliably produce pleasure or distress in oneself by conjuring up a familiar comforting or frightening fantasy, some idea of an object taken to be wholly unreal. But here the object upon which one acts in conjuring up the fantasy is the invented idea, not the object represented by that idea, and the real existence of ideas is unproblematic for Locke. Ordinarily, our pursuit of pleasure is not so much under our control: we take ourselves to act on objects whose natures lie outside the scope of our powers, with the expectation that they will satisfy us as they have in the past. Setting aside any Humean worries about the legitimacy of such expectations, the mode of thinking we call sensation instructs us concerning the ways in which these particular objects can be expected to behave. There is something to be said for setting pain and pleasure as an Archimedean point against which one will apply pressure to the skeptic. It is not obviously unreasonable to hold, as Locke does, that the appearance/reality distinction does not apply to pains and pleasures. Locke never expresses a concern that something might seem to be pleasure but not be pleasure, or that something might appear to be pain but not be pain: pain and pleasure are simple ideas, and as such are invariably real, adequate and true (2.20.1; 2.31.2; 4.4.4). The radical skeptic who contends that Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 34 all is a dream –even 'the glowing heat of a glass Furnace' – will still suffer pain as a consequence of putting his hand in it (4.11.8): whether or not the skeptic is ready to grant that he is faced with a real furnace, he will find himself experiencing real pain. If he acts in response to the pain, as Locke expects he will, the skeptic displays some kind of certainty concerning the reality of the furnace: he takes it to be real for practical purposes. Locke anticipates that the skeptic might attempt to insist on a distinction between what is taken to be real for practical purposes and what is actually known to exist. Locke resists this move by insisting that the purpose of our knowledge of outer existence is in any event practical. If the whole point of classifying objects as existent and nonexistent is to guide our actions, and if Locke is right to hold that our actions are guided by considerations of pain and pleasure, then we cannot be faulted for identifying objects as existent or nonexistent according to whether they do or do not serve as reliable sources of pleasure and pain. Looking back on this Lockean move after the emergence of Humean skepticism, Locke seems highly vulnerable to the charge that our past experience may not be any guide to whether an object is now or will in future be a reliable source of satisfaction or frustration. However, in the context of the forms of skepticism alive for Locke, in particular, the seventeenth‐century revival of Hellenistic skepticism, the appeal to the practical purposes of our rational faculties is not out of place. For the ancient skeptics, the practice of skepticism itself had a pragmatic justification: Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 35 achieving complete suspension of belief was supposed to result in mental tranquility. If Locke is able to show that our practical purposes are well served by our ordinary empirical methods of discerning which objects are real and unreal, then the skeptic whose ultimate aim is tranquility will be hard‐pressed to demand a higher form of certainty here. In refusing to demand more of our rational faculties than that they serve our practical purposes, Locke is maintaining a course charted early in the Essay. In the introduction he suggests that one aim of surveying the natural limits of the understanding is to reconcile ourselves to our inability to answer questions which lie beyond the range of our practical concerns (1.1.6). He goes on to argue that skepticism arises from a failure to understand the natural limits of the human understanding (1.1.7), a consequence which may be averted if we are willing 'to take a Survey of our own Understandings, examine our own Powers, and see to what Things they were adapted.' (1.1.7). In his final confrontation with the more radical form of skepticism, however, Locke simply states what one might wish him to prove: he relies very heavily on an assumption about the things to which our understandings were adapted. Locke's argument that the radical skeptic is asking for an unreasonable level of certainty depends on the premise that our knowledge of external objects must serve a practical function; any radical skeptic who does not share Locke's views about the function of human rationality will be unmoved. If Locke suffers from an incapacity to refute the most radical skeptic, however, he is Forthcoming in the Blackwell Companion to Locke, Matthew Stuart, ed. 36 not alone in this. If his real aim is to move the non‐skeptical reader, then a reminder of the practical inefficacy of skepticism is reasonable enough. Locke's account of sensitive knowledge has a number of gaps in it: in particular, the reader is left wanting a fuller explanation of the special kind of perception involved in perceiving the agreement of ideas, more details on the nature of our awareness of sensation as such, and more discussion of cases in which we are mistaken about whether we are sensing or merely imagining. Locke arguably makes more progress on the question of why we are not ordinarily affected by skeptical doubts than on the question of how such doubts could be rationally dispelled. But if a lasting inclination towards skepticism is as psychologically difficult for us as Locke seemed to think, the decision to address an audience not already inclined to skepticism is not a bad one. If 'no body can, in earnest, be so sceptical, as to be uncertain of the Existence of those Things which he sees and feels' (4.11.3), then there may be more value in exploring exactly why this is so, than in attempting to construct new arguments to bolster a certainty that is already 'as great as our frame can attain to'. Acknowledgements For helpful comments and discussion, I am grateful to Donald Ainslie, Hans Lottenbach, David Owen, Samuel Rickless, Sergio Tenenbaum and Shelley Weinberg. I would also like to thank the Social Sciences and Humanities Research Council of Canada for funding this research. 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