Locke on Empirical Knowledge forthcoming in History of Philosophy Quarterly v. 35, n. 4 (2018) Nathan Rockwood ABSTRACT This paper explores two related issues concerning Locke's account of epistemic justification for empirical knowledge. One issue concerns the degree of justification needed for empirical knowledge. Commentators almost universally take Locke to hold a fallibilist account of justification, whereas I argue that Locke accepts infallibilism. A second issue concerns the nature of justification. Many (though not all) commentators take Locke to have a thoroughly internalist conception of justification for empirical knowledge, whereas I argue that he has a (partly) externalist conception of justification: it is the fact that sensation is caused by an external object that justifies our belief in the corresponding object. So, while most commentators take Locke to be a fallibilist with an internalist conception of justification for empirical knowledge, I argue he is actually an infallibilist with an externalist conception of justification. §1 The Degrees and Nature of Justification Justification comes in degrees, and there is some disagreement about how much justification is needed for knowledge. Descartes famously holds that I cannot really know that p is true if it is possible for me, given my justification, to be wrong about p. Consequently, Descartes and like-minded epistemologists accept: Infallibilism: S meets the justification requirement for knowledge that p if and only if S's justification for believing that p entails (or guarantees) that p is true.1 Nowadays Infallibilism is almost universally rejected. In particular, it is now widely accepted both that sense perception can provide us with knowledge that material objects exist and yet such perception does not guarantee that material objects exist. The usual position is that justification makes the belief likely to be true (either because p is likely to be true given the available 1 For similar formulations of Infallibilism, as well as attributions to Descartes, see Cohen 1984, 280, and Reed 2012, 586, 591-592. 2 evidence, or because the belief that p was formed in a reliable way). Thus, nowadays epistemologists generally accept: Fallibilism: S meets the justification requirement for knowledge that p if and only if S's justification for believing that p makes it likely that p is true.2 The primary motivation for accepting Fallibilism is that it would allow us to grant the possibility (however unlikely) that our sensations are systematically mistaken while nonetheless avoiding skepticism (cf. Cohen 1984, 280; Reed 2012, 585). If Infallibilism were correct, then the mere possibility of perceptual error would undermine our ability to know on the basis of sensation that material objects exist. The way to avoid this skeptical conclusion, many have thought, is to lower the level of justification required for empirical knowledge; that is, if we want to maintain that we have knowledge that material objects exist then we should accept Fallibilism. So, does Locke accept Infallibilism or Fallibilism? The answer, most scholars think, depends on what the knowledge is about. We can know some things by perceiving an a priori necessary connection between the relevant concepts. For example, we do not need any empirical evidence to know that "all bachelors are unmarried men" or that "the interior angles of a triangle are equal to two right angles"; just by contemplating our ideas we can know that these propositions are true. Since such knowledge is not based on empirical observation, I will use "non-empirical knowledge" to refer to this kind of knowledge. By contrast, other things can be known only on the basis of empirical observation; I will use "empirical knowledge" to refer to this kind of knowledge. There are two kinds of empirical knowledge in Locke. First, he thinks we can have "sensitive knowledge" (i.e., knowledge based on sense perception) that material 2 For a similar formulation of Fallibilism, see Reed 2012, 587 (cf. Cohen 1984, 281). 3 objects exist (cf. E 4.2.14).3 Second, knowledge of the properties of material objects must come from observation rather than a priori reasoning (cf. E 4.12.9). It is widely acknowledged that Locke accepts Infallibilism with respect to non-empirical knowledge (Gibson 1917, 4; Ayers 1990, v. 1, 101-2; Newman 2007, 316-8). However, commentators almost universally claim that Locke accepts Fallibilism with respect to empirical knowledge (Lolordo 2008, Marusic 2016, and Rockwood 2016 are notable exceptions). Interpretations differ as to whether Locke is an internalist or externalist about justification with respect to sensitive knowledge, but the consensus view is that sensation provides only probabilistic justification for the existence of material objects. The internalist interpretations of Keith Allen (2013, 265), Shelley Weinberg (2013, 404), and Jennifer Nagel (2015, 323) all hold that, on Locke's view, the sensation of an object (along with the perception that this sensation agrees with another idea) provides us with sensitive knowledge that material objects exist, and yet they also maintain that our sensations could be mistaken. Lex Newman (2007, 325) claims that, in addition to the perception of an agreement between ideas, sensitive knowledge is partly constituted by a probabilistic judgment that our sensation corresponds to actual material objects. Samuel Rickless (2008, 85) holds that sensitive knowledge consists entirely in the probabilistic judgment that our sensations correspond to actual material objects.4 A probabilistic judgment of this sort, it is admitted by these interpreters, could be wrong. Similarly, the externalist interpretations of Martha Bolton and Aaron Wilson posit a correlation between sensations and 3 Locke's An Essay Concerning Human Understanding is cited as E and by book, chapter, and section. 4 It should be noted that Rickless takes Locke to be committed to Infallibilism about genuine knowledge, but since, on his interpretation, sensation provides only probabilistic justification for the existence of objects "sensitive knowledge" does not count as genuine knowledge (Rickless 2008, 93). 4 material objects which, on this view, justifies empirical knowledge (Bolton 2004, 304-7; Wilson 2014, 426). It is again admitted that we could have the sensation of a particular object even if that object did not actually exist (Bolton 2004, 318; Wilson 2014, 438). The common theme among all of these interpretations is that our sensation of material objects is the basis for sensitive knowledge and yet it is possible that, in a given case, our sensation does not correspond to an actual material object. Further, if sensation gives us only probabilistic justification for the existence of objects then apparently sensation would likewise provide only probabilistic justification concerning the properties of those objects. Thus, the only hope for securing knowledge of the existence and properties of objects, so it would seem, is to accept Fallibilism with respect to empirical knowledge. Going against the predominant scholarly opinion, however, I argue in this paper that Locke accepts Infallibilism with respect to empirical knowledge and that on his view we succeed in obtaining knowledge concerning the existence and properties of material objects. An immediate consequence of combining these two theses is that Locke must deny that it is possible for us to have the sensations we actually have if material objects do not exist. Indeed, I will argue that there is compelling textual evidence that Locke does just that. This position will no doubt strike epistemologists nowadays as obviously false since Descartes's hypothesis that an evil demon causes all of our sensations seems like a legitimate possibility. But we take the evil demon hypothesis to be possible only because we are more impressed with Descartes's skeptical arguments than with his proposed solution (cf. Cohen 1984, 280). I will argue that Locke, like Descartes himself by the end of the Sixth Meditation, rejects the hypothesis that our sensations could be mistaken. In that case, the sensation of objects entails (or guarantees) the existence of 5 those objects. Once we recognize this feature of Locke's position, we can see how he can accept both Infallibilism and that sensations gives us empirical knowledge of material objects. In addition to the debate concerning the degree of justification Locke thinks is required for empirical knowledge, a related issue of interpretation concerns his view on the nature of this justification. Descartes famously argues that if I am not aware of reasons to believe that I am awake rather than asleep then I cannot really know that I am awake. Thus, Descartes and likeminded philosophers accept: Internalism: The justification for S's belief that p consists in (and is exhausted by) a mental state of S that provides evidence (or reason to believe) that p is true.5 By contrast, any theory that allows for the justifying condition to be something other than a mental state (i.e., some fact external to my awareness) is an externalist theory of justification: Externalism: The justification for S's belief that p may consist in something other than a mental state of S. Suppose, for example, I have the sensation of seeing a table and thereby form the belief that a table exists. According to Goldman's Causal Theory of Knowledge, my belief that the table exists is justified by the causal relation that holds between the table and my belief that the table exists (Goldman 1967). Because this causal relation is not itself a mental state, and yet on his view it justifies my belief, this counts as an externalist theory of justification. The second issue in this paper, then, is whether Locke accepts Internalism or Externalism about the nature of justification. As noted above, several interpreters take the one and only requirement for sensitive knowledge to be the perception of a relation between ideas, while others take sensitive knowledge to require (either solely or in addition to the perceived 5 For a similar formulation of Internalism, see Feldman and Conee 2001, 2. 6 agreement) a probabilistic judgment that our sensations correspond to material objects. On these interpretations, Locke is an internalist since the justifying condition is an internal mental state. The majority view represented in the literature, then, is that Locke is an internalist about justification for empirical knowledge. By contrast, Bolton (2004) and Wilson (2013) argue that on Locke's view the causal relation between sensations and their corresponding material objects justify empirical knowledge. I will argue below that, on Locke's account, sensitive knowledge requires both that sensations are caused by material objects and that we recognize this sensation as a sensation. Notice that on this interpretation Locke holds that a mental state is necessary for, and contributes to, the justification for empirical knowledge. I will call this an "internalist requirement" for empirical knowledge since Internalism requires that there be a mental state providing justification. Unlike a fully internalist position, however, Locke does not take the mental state to be sufficient for empirical knowledge; he also holds that the causal relation between sensation and external objects is necessary for, and contributes to, the justification for empirical knowledge. I will call the latter an "externalist requirement" since Externalism (unlike Internalism) allows for something other than a mental state to provide justification. According to Locke, as I interpret him, to have empirical knowledge we must satisfy both of these requirements. Nonetheless, because his view takes something other than mental states to provide justification, Locke's view is a kind of Externalism. So, on the two major issues concerning Locke's theory of justification I take the minority position. Most take Locke to accept Fallibilism and Internalism with respect to empirical knowledge, whereas I argue here that Locke accepts Infallibilism and Externalism. Let me now convince you that I am right. 7 §2 Locke on Certainty and Sensation The first tip that Locke accepts Infallibilism is that, following Descartes, Locke insists that knowledge requires certainty. Locke says, "to know and be certain, is the same thing...and what comes short of certainty, I think cannot be called knowledge" (Works 4, 145).6 For Descartes, the mere possibility of being mistaken undermines certainty, and thus to be certain that p means having justification that entails that p is true. Locke likewise thinks of certainty as having justification that entails truth. Suppose my justification that p makes it very likely that p is true, but does not rule out the possibility that p is false. In that case, Locke would deny that I know that p "Because the highest Probability, amounts not to Certainty; without which, there can be no true Knowledge" (E 4.3.14, my emphasis in bold; cf. 4.15.4). I cannot know that p so long as there is the possibility, however unlikely, that p is false given my justification. That is Infallibilism: knowledge requires certainty, and certainty is when justification entails truth. Locke repeatedly insists that sensation gives us certainty concerning the existence of material objects. He introduces sensitive knowledge as one of the "three degrees of Knowledge" that correspond to three "degrees and ways of Evidence and Certainty" (E 4.2.14, my emphasis in bold). Elsewhere, he refers to the "certainty of our Senses" that "makes us know that something doth exist at that time without us" (E 4.11.2, my emphasis in bold), and insists that "no body can, in earnest, be so sceptical as to be uncertain of the Existence of those Things which he sees and feels" (E 4.11.3, 631, my emphasis in bold). Further, this certainty is not merely a high probability: "If I my self see a Man walk on the Ice, it is past Probability; 'tis Knowledge" (4.15.5, my emphasis in bold). Locke thinks of certainty as having justification that 6 The Works of John Locke are cited as Works and by volume and page numbers. 8 entails the truth of the belief, and he thinks that sensation can provide us with this kind of certainty. Locke also denies that knowledge of material objects extends beyond my sensation of them precisely because in such cases it is possible for me to be wrong. Suppose, for example, I see Jack at t1 but not at t2. Can I know, on the basis of my sensation at t1, that Jack exists at t2? Locke does not think so: For if I saw...[a] Man, existing...one minute since, and am now alone, I cannot be certain, that the same Man exists now, since there is no necessary connexion of his Existence a minute since, with his Existence now: by a thousand ways he may cease to be since I had the Testimony of my Senses for his Existence. ...And therefore though it be highly probable...I have not that Certainty of it, which we strictly call Knowledge; though the great likelihood of it puts me past doubt...this is but probability, not Knowledge. (E 4.11.9, my emphasis in bold) I cannot know that Jack exists at t2 because my sensation at t1 does not entail that Jack exists at t2 ("by a thousand ways he may cease to be" since I saw him at t1). So even though it is "highly probable" that Jack exists at t2, I cannot be certain of this, and hence I do not know it. One lesson here is that, again, high probability falls short of empirical knowledge. This is a rejection of Fallibilism; Locke holds instead that in order for me to have empirical knowledge my sensation must guarantee the truth of my belief. But does my sensation at t1 allow me to be certain that Jack exists at t1? If my sensation at t1 made it probable, but not certain, that Jack exists at t1, then for the same reason that Locke denies that I know that Jack exists at t2 he should also be denying that I know that exist at t1. What Locke does instead, though, is insist on a difference between these two sorts of cases. Locke says that while we perceive an object "we cannot but be satisfied, that there doth something at that time really exist without us, which doth affect our Senses", yet "this Knowledge extends as far as the present Testimony of our Senses, employ'd about the particular 9 Objects, that do then affect them, and no farther" (E 4.11.9). In this passage, Locke draws a contrast between the knowledge and certainty that an object exists while I perceive it and the high probability that it continues to exist after I no longer perceive it (cf. Allen 2013, 252-3). This contrast requires that my sensation of Jack at t1 entails that Jack exists at t1, whereas this sensation at t1 merely makes it probable that Jack exists at t2. This again shows that he accepts Infallibilism. Several commentators contrast the certainty of sensitive knowledge with that of highly probable beliefs, yet they do not follow this implication all the way to its logical conclusion. Commentators tend to say, even though on their view sensitive knowledge is a kind certainty beyond merely a probabilistic judgment, it is possible that our sensations of objects could be mistaken (Allen 2013, 265; Weinberg 2013, 404; Nagel 2015, 323). But if it is possible for my belief that Jack exists while perceiving him to be mistaken, then my perception of Jack can at best give me highly probabilistic evidence that Jack exists. The inevitable conclusion we should draw from this example, then, is that Locke accepts Infallibilism with respect to sensitive knowledge. At this point, we can see considerable evidence that, for Locke, the sensation of objects entails that those objects actually exist. Let us take this as settled. Still, we might then wonder what it is that we know exists. An extremely modest conclusion would be that we know that something exists that causes our sensations, but we do not know what properties this something has (Bolton 2004, 306; Newman 2007, 333). A more optimistic conclusion is that we can know that it is material objects causing our sensations, and on the basis of sensations we can have knowledge about (some of) the properties of those objects (Lolordo 2008; Marusic 2016; 10 Winkler, ms.). I will now argue that Locke adopts the more optimistic position; that is, he thinks we can have empirical knowledge of the properties of material objects. According to Locke, there are two ways to gain knowledge about the properties of material objects, which he categorizes as knowledge of "coexistence" (i.e., the coexistence of properties). One way to have such knowledge, he says, is "by [perceiving] the necessary connexion of the Ideas [of those qualities]" (E 4.3.14); this is non-empirical knowledge since it comes by an a priori contemplation of our ideas. However, this kind of knowledge "is yet very narrow, and scarce any at all. The reason whereof is, that...for the most part" our idea of one property has "no visible necessary connexion" with any other property (E 4.3.10; cf. 4.3.14). Locke's response to the dearth of a priori knowledge of coexistence is to refer us to empirical observation: "Experience here must teach me, what Reason cannot". He continues: 'tis by trying alone, that I can certainly know, what other Qualities co-exist with those of my complex Idea, v.g. whether that yellow, heavy, fusible Body, I call Gold, be malleable, or no; (E 4.12.9, my emphasis in bold) By observing a particular bit of gold "I can certainly know" that the qualities of yellow, heavy, and fusibility co-exist with malleability. However, Locke goes on to restrict this knowledge to "that particular Body". He then ends the section by saying, concerning the coexistence of qualities, "I must apply my self to Experience; as far as that reaches, I may have certain Knowledge, but no farther" (E 4.12.9, my emphasis in bold). Elsewhere, he says, we can know that two (or more) properties coexist in one object "by the observation of our Senses" (E 4.3.14). On Locke's view, then, sensation can give us empirical knowledge that a particular object has two (or more) properties. Not only does Locke endorse the view that we can know that two properties coexist in the same object, he also denies that probability is sufficient justification for such knowledge: 11 ...because no one of these Ideas has any evident dependence, or necessary connexion with the other, we cannot certainly know, that where any four of these [qualities] are, the fifth [quality] will be there also, how highly probable soever it may be: Because the highest Probability, amounts not to Certainty; without which, there can be no true Knowledge. (E 4.3.14, my emphasis in bold) He, again, claims here that we cannot have certainty that two properties always coexist. However, he does allow that such connections may be "highly probable". Yet he explicitly rejects the view that having highly probable justification for a coexistence claim counts as having knowledge. Further, he elsewhere takes "constant and never-failing Experience" of a regularity to provide the "highest degree of Probability" but then again asserts that such highly probable judgments "come not within the reach of our Knowledge" (E 4.16.6). So, Locke (1) affirms that sensation provides the justification needed for empirical knowledge that an object has certain properties, and (2) denies that this justification is fallible. The claims (1) and (2) commit Locke to the view that knowledge of coexistence, based on sensation of particular objects, satisfies the justification requirement of Infallibilism. Now, it is not a consequence of my interpretation that all beliefs based on sensation are correct (that would be absurd). On the interpretation I am offering, then, I claim only that, according to Locke, sensations can and often do satisfy the justification requirement of Infallibilism. Specifically, on my interpretation, what we can know on the basis of sensation is that there is an object with the properties we observe in it. An object, for Locke, is a bundle of properties plus a substance that has these properties (E 2.23.1-4). We divide particular objects into kinds by their "nominal essence", or an observable set of properties (E 3.4.2). Locke claims that we can know, on the basis of observation, that an object of a given kind (i.e., something with a set of properties) exists. For example, Locke claims that we can know on the basis of seeing a man that he exists (E 4.11.9; 4.15.5), and on the basis of observation that water exists (E 12 4.11.11), and on the basis of sensation that a piece of paper exists (E 4.11.2), et cetera. In short, sensation can and often does provide infallible justification for believing that objects exist with the properties we perceive them to have. The account I am here attributing to Locke asserts that sensation can satisfy the justification requirement of Infallibilism, but only for beliefs about the existence and properties of objects that we observe. However, most commentators would think that the view I am attributing to Locke is much too optimistic, given the obvious possibility of perceptual error. I turn now, then, to the skeptical arguments in the First Meditation and Locke's reply to them. §3 Skeptical Doubt Locke claims that sensation can provide us with knowledge of material objects. Given Descartes's skeptical argument, of which Locke was certainly aware, Locke is then forced to choose between accepting Fallibilism or rejecting the possibility that our sensations are dreams or the deceptions of an evil demon. As noted above, the recent literature has interpreted Locke as accepting Fallibilism. However, in this section, I will argue that Locke rejects the possibility of the skeptical hypothesis and that doing so allows him to maintain a commitment to Infallibilism while also insisting that we can succeed in obtaining empirical knowledge. A central premise in Descartes's skeptical arguments is that my experience which corresponds to actual material objects is subjectively indistinguishable from an experience which does not correspond to material objects. In one version of the argument, Descartes points out that, even though I am having the perceptual experience of sitting near the fire, "a man who sleeps at night...has all the same experiences" (Meditations, 13, my emphasis). In another version of the argument, he suggests that my perceptions of "the sky, the air, the earth, colours, 13 shapes, sounds, and all external things are merely the delusions of dreams which [the evil demon] has devised to ensnare my judgment" (Meditations, 15). The point here again seems to be that I could have an experience subjectively indistinguishable from actually sensing objects even when there are no such objects. Consequently, if I form a belief that I am sitting by the fire (only) on the basis of my experience, then there is a possibility that I may be wrong. Hence, according to Infallibilism, I cannot know on the basis of my experience that I am sitting by the fire. However, Descartes is no skeptic. He takes himself to have made a logical proof that shows decisively that God exists (Third Meditation) and is no deceiver (Fourth Meditation). Since God is no deceiver, this rules out the evil demon hypothesis as impossible (Meditations, 55). By the end of the Mediations, he also rejects the dream hypothesis because "I now notice there is a vast difference between the two" (Meditations, 61, my emphasis). By insisting on a subjectively distinguishable difference between dreaming and being awake, along with a guarantee that God would not deceive me in my waking experience (Meditations, 61-2), Descartes can now conclude that our waking experiences correspond to external objects. That is, Descartes concludes that I can, after all, be certain that I am sitting by the fire. We have seen that Descartes's skeptical arguments rely on two assumptions: one assumption is Infallibilism, and the second is that sensation of a material object is subjectively indistinguishable from other experiences I could have (e.g., dreaming or being deceived). If Locke were to accept both of these assumptions, he would not be able to avoid skepticism. Since Locke accepts Infallibilism, and yet insists that we can succeed in obtaining empirical knowledge, the only way out of the skeptical argument is to follow Descartes in denying the indistinguishability assumption, and that is exactly what Locke does. 14 Locke introduces sensitive knowledge as the third degree of knowledge and then notes that "some Men think that there may be a question made" about whether an object "corresponds to that Idea" "because Men may have such Ideas in their Minds, when no Thing exists, no such Object affects their Senses" (E 4.2.14). That is, some people think that it is possible to have a sensation without there being a corresponding object. Locke replies: 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. (E 4.2.14, my emphasis in bold) And elsewhere he says: there is a manifest difference, between the Ideas laid up in my Memory [and sensation] (E 4.11.5, my emphasis in bold) Locke insists that there is a qualitative difference between an occurrent sensation of an object and my memory of the object. While skeptical arguments are typically not directed towards the inability to distinguish sensation from memory, Locke's reply here is part of a larger theme: sensations are subjectively distinguishable from other kinds of ideas. The above-quoted passage continues with Locke considering the possibility that I am dreaming: someone might say that "a Dream may do the same thing [as sensation], and all these Ideas may be produced in us, without any external Objects". In the First Meditation, for example, Descartes imagines the possibility that my sensation of the fire in front of me is really just a dream. Locke responds directly to this example: "I believe he will allow a very manifest difference between dreaming of being in the Fire, and being actually in it" (E 4.2.14). Similarly, he later considers someone (e.g., Descartes in the First Meditation) who is 15 so sceptical as to distrust his Senses, and to affirm, that all we see and hear, feel and taste, think and do, during our whole Being, is but the series and deluding appearances of a long Dream... Locke replies to this skeptic: And if our Dreamer pleases to try, whether the glowing heat of a glass Furnace, be barely a wandering Imagination in a drowsy man's Fancy, by putting his Hand into it, he may perhaps be wakened into a certainty greater than he could wish, that it is something more than bare Imagination. (E 4.11.8, my emphasis in bold) If I put my hand into an actual fire then I would be certain that it is an actual fire, presumably because putting my hand in an actual fire would be painful in a way that merely dreaming about putting my hand in the fire is not (cf. E 4.11.7). Locke replies to the skeptical argument, then, by rejecting the claim that sensation is subjectively indistinguishable from dreaming. Locke is much less explicit about his reply to the skeptical worry that sensations are merely the deception of an evil demon. In the passage quoted above, the skeptic worries that sensations are just "deluding appearances", which I take to be an allusion to Descartes's evil demon hypothesis. If this is right, then his reply to evil demon hypothesis is that the deluding experiences are (again) subjectively distinguishable from veridical sensation. Here we might fault Locke for a failure of imagination. Indeed, he is clearly wrong on this point. But this is the most direct reply to the evil demon hypothesis that I can find. Perhaps a second, implicit reply to the evil demon hypothesis is that God would not allow us to be deceived in this way. For God is responsible for how we perceive objects (E 4.3.28), yet God is no deceiver (Works 4, p. 187). This may be why he says, "I think God has given me assurance enough of the Existence of Things without me", and he expresses "confidence that our [sense] Faculties do not herein deceive us" (E 4.11.3). So, Locke may be following Descartes in thinking that there is a divine guarantee that our sensations correspond to material objects. In that case, he could consistently deny the evil demon hypothesis. 16 To be successful, the skeptical argument needs there to be two possible and subjectively indistinguishable worlds: in W1 I am having the sensation of the fire which corresponds to an actual fire, and in W2 I am having the sensation of the fire when there is no fire (e.g., when dreaming or being deceived). But Locke denies that W2 is a possible world. The result is that, on his view, there is a necessary connection between my sensation of the fire and the actual fire. This a rather dubious claim, but suppose, for the sake of argument, that he is right. In that case, given my sensation, I cannot be wrong that I am sitting by the fire. The dream hypothesis and evil demon hypothesis are supposed to raise the possibility of error. Locke obviates this line objection by making my sensation of being by the fire necessarily connected to the truth of my belief that I am sitting by the fire. Thus, on this view, sensations can satisfy the justification requirement of Infallibilism. The skeptic will no doubt be unsatisfied with Locke's account for two reasons. First, the skeptic will insist that W2 (in which my sensation is mistaken) is indeed a possible world. Second, the skeptic will likely insist that to have knowledge that the fire exists I would need to prove that my sensation of the fire has a necessary connection to the actual existence of the fire. However, this objection assumes that Locke accepts an internalist account of justification according to which only mental states can provide justification. According to Externalism, by contrast, some fact about the world (of which we may or may not be aware) can provide justification. I will now argue that Locke takes the fact that, in his view, there is a necessary causal connection between sensations and corresponding material objects as justification for empirical knowledge. As an externalist account, empirical knowledge would not require us to prove that it is impossible for our sensations to be mistaken. I turn now, then, to Locke's externalist account of justification. 17 §4 Locke on the Nature of Justification Locke defines knowledge as the perception of an agreement between ideas, and for this reason commentators usually take Locke to have an internalist requirement for empirical knowledge. I agree with this much of the standard interpretation of Locke and so I will have only a little to say about how, on Locke's view, this justification requirement is satisfied. My interpretation differs from the standard interpretation, however, in that, on my view, something other than a mental state contributes the justification of empirical knowledge: namely, the fact that the sensation has an external cause contributes to the justification of empirical knowledge. This makes Locke's account a kind of Externalism. Locke accepts an internalist account of justification insofar as empirical knowledge requires a certain kind of mental state. He defines knowledge as the perception of an agreement or disagreement between ideas (E 4.1.2), and he identifies the two ideas that are perceived to agree in the case of sensitive knowledge: Now the two ideas, that in this case are perceived to agree, and thereby do 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. (Works 4, 360) We have seen Locke elsewhere insists that empirical knowledge depends on the sensation of an object, so this sensation must either be "the idea of actual existence of something" or "the idea of actual sensation". Locke sometimes uses "actual existence" to refer to material objects (e.g. E 4.1.7; cf. Rockwood 2016, 44-5), which suggests that "the idea of actual existence of something" is the sensation or idea of a material object. The second idea, I take it, is an idea of reflection, or a second-order awareness of my current mental state. According to Locke, I can reflect on the action of my own mind and thereby form an idea of what it is that my mind is doing (E 2.1.4). In 18 particular, "When we see, hear, smell, taste, [or] feel...any thing, we know that we do so" (E 2.27.9). That is, my sensation of an object is always accompanied by a second-order awareness that I am having a sensation. Locke seems to be identifying this second-order idea as the second idea in sensitive knowledge.7 Locke's view, then, is that we have knowledge that a material object exists only when we both have the sensation of an object and we recognize this sensation as a sensation. This is an internalist justification requirement because a certain kind of mental state (i.e., the awareness of the sensation as a sensation) is necessary for, and contributes to, the justification of empirical knowledge. I will now argue that on Locke's view there is a second justification requirement for empirical knowledge and that this is an externalist requirement. The first argument in favor of this view is a theoretical point: if the perception of the agreement between ideas were the only requirement for empirical knowledge, then the justification for my belief that an object exists would not be connected in the right kind of way to the truth of my belief that the object exists. Consider, for example, Jennifer Marusic's interpretation of Locke. She rightly argues that Locke accepts Infallibilism with respect to empirical knowledge, which she correctly takes to imply that I can have the sensation of a material object if and only if that material object is causing my sensation (cf. Marusic 2016, 215-6, 232). She then claims, though, that "sensitive knowledge consists in perceiving an agreement or disagreement between ideas" (Marusic 2016, 232). Thus, she sees the justification in sensitive knowledge as being exhausted by the perception of the relation between these ideas. She does take the causal connection between sensation and an external object to be a necessary condition for empirical knowledge. However, on her view, only 7 For a similar interpretation, see Allen 2013, 256-258; Weinberg 2013, 411; and Nagel 2015, 325. For criticism of this line of interpretation, see Wilson 2014, 435-438; and Marusic 2016, 212-213. 19 mental states (do and can) justify empirical knowledge. Thus, by hypothesis, her interpretation excludes the existence of an object, and its causal connection to sensation, from contributing to the justification for empirical knowledge. For this reason, the justification for my belief that an object exists is entirely divorced from the fact that this object exists and is causing my sensation. This seems problematic. The justification for my belief that an object exist should, presumably, have some connection to the truth of my belief. Intuitively, then, the justification itself (and not some further fact external to the justification) should be the thing guaranteeing that the belief is true. So, an internalist interpretation of sensitive knowledge seems problematic from a theoretical point of view and, as I argue below, contrary to what Locke himself says about sensitive knowledge. The above criticism generalizes to most other interpretations of Locke currently on offer. Everyone grants that Locke thinks that sensations are caused by material objects. They even appeal to this causal relationship, as Marusic does, to explain why Locke thinks we succeed in having knowledge of material objects (e.g., Allen 2013, 264; Nagel 2015, 326). But these authors take the justification for empirical knowledge to consists solely in the perception of an agreement between ideas and thereby they exclude the causal relationship from the justification of empirical knowledge. In that case, the justification for my knowledge that an object exists will have nothing whatever to do with the actual existence of the object! Here, my externalist interpretation differs: although the justification for empirical knowledge partly consists in a mental state (i.e., identifying a sensation as a sensation), it also partly consists in the fact that the sensation is caused by an external object. The latter, externalist causal condition posits a plausible connection between justification and empirical knowledge, whereas the internalist requirement alone fails to do so. 20 A second argument for my externalist interpretation is that Locke seems to say that sensitive knowledge is justified by the fact that sensations are caused by external objects. Locke denies that merely "having the idea of any thing...proves the existence of that thing" (E 4.11.1), and then says, "'Tis therefore 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" (E 4.11.2, my emphasis in bold). The subject of the indirect statement is "the actual receiving of Ideas from without" and the predicate is "makes us know". So, the fact that the sensation has an external cause provides justification. He then adds, "though perhaps we neither know nor consider how" a sensation is causally connected to a corresponding material object, this "takes not from the certainty of our Senses" (E 4.11.2). This is an acknowledgement that although the causal connection between sensations and material objects provides the justification for sensitive knowledge, it is not necessary to even "consider" this relation in order to know that material objects exist. Hence, on Locke's view, the fact that an object causes my sensation provides externalist justification. There is more evidence of the same kind. Locke says, "no particular Man can know the Existence of any other Being, but only when by actual operating upon him, it makes it self perceived by him" (E 4.11.1). Elsewhere, he says that we have sensitive knowledge "By Sensation, perceiving the Existence of particular Things" (E 4.3.2; cf. 4.9.2). These passages suggest that, for Locke, it is the causal relation between sensations and their corresponding material objects (and not just the content of the ideas) that justifies sensitive knowledge. Locke's position, then, is as follows. First, we have the sensation of a material object, along with a higher-order awareness (or idea of reflection) that identifies this sensation as a sensation. Second, the sensation of the material object has a necessary causal connection to the 21 actual existence of the material object. Satisfying these two conditions entails that there actually exists a material object, with the qualities we perceive it to have, corresponding to our sensation. Given that Locke takes these to be the requirements for empirical knowledge, he can consistently maintain, even as a proponent of Infallibilism, that satisfying these requirements provides us with certain knowledge that material objects exist. §5 Further Considerations If Locke were to accept Infallibilism and Externalism with respect to the justification for empirical knowledge, as I have suggested, then a couple of lingering question remain. Locke offers four arguments to believe that our sensations of objects correspond to material objects (E 4.11.4-7). Commentators widely take these to be probabilistic arguments (Newman 2007; Rickless 2008; Weinberg 2013). But if the justification from sensation is infallible, then why give these probabilistic arguments? My reply is twofold. First, as others have pointed out (Allen 2013, 2015; Weinberg 2013, 390), the concurrent reasons are given in addition to "the assurance we have from our Senses themselves, that they do not err in the Information they give us, of the Existence of Things without us, when they [i.e., the senses] are affected by them [i.e., those external objects]" (E 4.11.3, my emphasis in bold). Locke here suggests that the senses provide their own justification for our belief in material objects, and then he says "we are farther confirmed in this assurance, by other concurrent Reasons" (E 4.11.3, my emphasis in bold). The arguments Locke offers here, then, are distinct from the justification that sensation itself provides for empirical knowledge. This fits nicely with my externalist interpretation. 22 Second, contrary to what commentators repeatedly claim, the first two arguments are not probabilistic arguments: they are demonstrations. The first concurrent reason for believing sensations correspond to material objects is that, via Locke's empiricism, it is impossible for us to have ideas without them being caused by external objects. The title of this section is, "First, Because we cannot have them [i.e., the ideas] but by the inlet of the Senses" (E 4.11.4, section heading, my emphasis in bold). In the section he argues that "those that want the Organs of any Sense, never can have the Ideas belonging to that Sense produced in their Minds". Someone without eyes cannot see, and Locke takes this to show that "we cannot but be assured, that [those ideas] come in by the Organs of that Sense, and no other way" (E 4.11.4, my emphasis in bold). There is one and only way to have a certain kind of idea: from a sensation caused by an external object. This is not a tentative conclusion. If we cannot have an idea of the taste of a pineapple without this idea (first) being a sensation caused by an external object, then our having the sensation of this taste entails that this sensation really is caused by a pineapple (cf. E 4.11.4). The second concurrent reason is even clearer. Locke suggests that I should believe that external objects are causing my sensation, "Because sometimes I find, that I cannot avoid the having of those Ideas produced in my mind." For example, "if I turn my Eyes at noon towards the Sun, I cannot avoid the Ideas, which the Light, or the Sun, then produce in me." Unlike ideas of imaginations and memory, which are under my voluntary control, sensations "force themselves upon me, and I cannot avoid having" them. Because of the involuntary nature of sensation, Locke concludes, "therefore it must needs be some exterior cause...that produces those Ideas in my Mind...And therefore he hath certain knowledge...that actual seeing hath a Cause without" (E 4.11.5, my emphasis in bold). Again, these are not tentative conclusions. 23 Locke's concurrent reasons for believing our sensations correspond to material objects reveal that, in his view, there is a necessary connection between sensation and corresponding material objects. According to the first concurrent reason, I cannot have the sensation of x unless x causes this sensation. According to the second concurrent reason, the sensation of x is involuntary, and so if my organs are directed towards the object (et cetera) this is sufficient for me to have the sensation of x. Thus, I will have the sensation of x if and only if x is causing me to have that sensation. If these arguments are successful, then this would establish a necessary connection between sensations and corresponding external objects. So, Locke attempts to argue for the kind of causal relation that his theory needs in order for sensations to satisfy the justification standard of Infallibilism. For this reason, the concurrent reasons provide further evidence for my interpretation. Another kind of worry about the interpretation I am defending is that there would be no explanation for why empirical knowledge is less certain than non-empirical knowledge. We have non-empirical knowledge by the contemplation of our own ideas, either by intuition or demonstration. Locke takes intuition and demonstration to be more certain than sensitive knowledge (E 4.2.14; 4.11.3). But if in sensitive knowledge the justification is such that it entails the truth of my belief then, goes the worry, this does not leave any room for me to be less certain with respect to sensitive knowledge than I am about non-empirical knowledge from intuition and demonstration. However, demonstration is also less certain than intuition, yet both intuition and demonstration satisfy the justification requirement of Infallibilism. In Locke's view, then, there can be degrees of certainty while remaining certain. Given this, Locke can consistently claim that sensitive knowledge is less certain than demonstration and yet remains certain (cf. Allen 2013, 262). 24 While I take the above point to be sufficient to show that the objection is mistaken, it would be even better if, in addition to the point just made, I offer some explanation (consistent with Infallibilism) as to why sensitive knowledge is less certain than non-empirical knowledge. I suggest the following (cf. Rockwood 2016, 61-3). First, while Locke characterizes the difference between intuitive and demonstrative knowledge in several ways, one relevant difference seems to be that in intuition the agreement between two ideas is immediately apparent (E 4.2.1), whereas in demonstration the agreement may not be perceived even when it is present. Locke offers the latter point as an explanation for why the evidence of demonstrative knowledge "is not altogether so clear and bright" (E 4.2.4). Perhaps, then, the degrees of certainty can be explained by how apparent the connection is between the ideas, rather than the certainty of such a connection. In particular, if the agreement between ideas in sensitive knowledge were less apparent than the agreement in a typical demonstration, then this could explain why sensitive knowledge is less certain than demonstrative knowledge. Second, sensitive knowledge requires identifying a sensation as a sensation, and the idea of that we are currently having a sensation is an idea of reflection. Locke holds that such ideas are less apparent to us than ideas of sensation (cf. E 2.1.7-8). And if the reflective idea of having a sensation is not readily apparent, then neither is the perceived agreement between that idea and the sensation of an object. In which case, according to the proposal, sensitive knowledge may for this reason be less certain than demonstration. A similar story could apply for knowledge of coexistence based on sensation of the properties of objects. I take this to be a plausible explanation for why Locke takes empirical knowledge to be less certain than non-empirical knowledge, though other explanations are certainly possible. 25 In this section I have considered a variety of worries about attributing Infallibilism to Locke, yet none of these worries is ultimately persuasive. There is good reason, then, to interpret Locke as accepting Infallibilism with respect to empirical knowledge. §6 Conclusion: Locke, Infallibilism, and Externalism It is often assumed that accepting Infallibilism inevitably leads to skepticism about the existence of material objects, since it seems possible that all of our experiences are really a dream or the deception of an evil demon. So, if we want to insist that we have knowledge of material objects we should accept Fallibilism. Moreover, many commentators have interpreted Locke as making this sort of move. However, I have argued that Locke escapes the skeptical argument while still endorsing Infallibilism. Locke's insistence that sensitive knowledge meets the standard of justification required by Infallibilism is made possible by his denial of the subjective indistinguishability assumption. He claims that there is a qualitative difference between sensations and all other ideas, and that we can infallibly identify sensations as sensations. Further, sensations have a necessary connection to the actual existence of corresponding material objects. On this sort of view, if we have the sensation of a fire, and we recognize it as such, then this justification entails that the fire actually exists. Contrary to what many have assumed, then, Locke can accept Infallibilism while also maintaining that sensation provides knowledge that material objects exist. We have also seen that Locke takes the fact that sensations are caused by material objects as part of the justification for empirical knowledge. Since something other than a mental state contributes to the justification of empirical knowledge, Locke's account of justification is externalist. 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