Natural Instinct, Perceptual Relativity, and Belief in the External World in Hume's Enquiry

Abstract

In part 1 of Enquiry 12, Hume presents a skeptical argument against belief in external existence. The argument involves a perceptual relativity argument that seems to conclude straightaway the double existence of objects and perceptions, where objects cause and resemble perceptions. In Treatise 1.4.2, Hume claimed that the belief in double existence arises from imaginative invention, not reasoning about perceptual relativity. I dissolve this tension by distinguishing the effects of natural instinct and showing that some of these effects supplement the Enquiry's perceptual relativity argument. The Enquiry's skeptical argument thus reveals the fundamental involvement of natural instinct in any belief in external existence.

In both Treatise 1.4.2, "Of scepticism with regard to the senses," and the first part of Enquiry 12, "Of the Academical or Sceptical Philosophy," Hume addresses the vulgar belief that we directly sense external objects. He describes philosophical arguments, drawing upon the phenomenon of perceptual relativity, that purport to show the falsity of the vulgar belief. Because of this conclusion, non-skeptical philosophers are moved to distinguish between perceiver-dependent perceptions and perceiver-independent objects, attributing external existence to entities of the latter category only. But there is a puzzling difference in the two accounts of this dialectic. In the Treatise, Hume argues that the perceptual relativity argument suffices only to reject the vulgar belief; it is by itself insufficient to introduce the double existence of objects and perceptions, where perceptions resemble their ancestral objects. Instead, that hypothesis depends upon the persistent effects of natural imaginative propensities. In contrast, in the Enquiry, the double existence of objects and perceptions seems to be drawn straightaway from the phenomenon of perceptual relativity.

One might think that Hume simply changes his mind in the later work. However, in the Enquiry, following the presentation of the philosophical system, Hume points out that the philosophical system is "without any foundation in reasoning" (EHU 12.12; SBN 153),¹ which is exactly the criticism that he makes in the Treatise (T 1.4.2.47; SBN 212).² So it seems inappropriate to conclude that he has changed his mind.

Thus, it seems that Hume purports to argue from the phenomenon of perceptual relativity to the double existence of perceptions and objects in the Enquiry.³ In general, commentators find this argument to be unsatisfactory, either because it is unsound⁴ or because it fails to establish the double existence of objects and perceptions.⁵ I contend that the argument does not exclusively employ reasoning about perceptual relativity. Additional premises are to be found in some of the effects of natural instinct described prior to the discussion of perceptual relativity. I distinguish the effects of natural instinct that Hume describes. The perceptual relativity argument contradicts only some of these effects and philosophers (perhaps unwittingly) draw upon other effects to ground their philosophical system. This interpretation accords well with Hume's claims in the Treatise: the philosophical system is the combined product of reason and the imagination.

My overall claim in this paper is that, according to Hume as scientist of human nature, natural instinct plays an indispensable role in any belief in external existence. In particular, I argue that the effects of instinct serve as premises in the Enquiry's perceptual relativity argument, which I shall call the "Diminishing Table Argument."⁶ To that end, first I show that the content of the vulgar belief in the existence of body is the same in the Treatise and the Enquiry. Thus, both perceptual relativity arguments include among their aims showing the falsity of the same vulgar belief. Then I examine the Treatise's perceptual relativity argument, which I shall call the "Double Vision Argument," and Hume's discussion of its limited scope. To wit, the argument shows the falsity of the vulgar belief that what is directly and immediately perceived exists externally. But from the phenomenon of perceptual relativity, one cannot conclude straightaway that perceptions resemble their ancestral objects; most of that philosophical belief arises from imaginative invention. Next, I turn to the Enquiry. Following Hume, I distinguish "trite topics" from "more profound arguments" against the evidence of sense. The relevant perceptual relativity argument occurs as part of an argument in the latter group. I argue that the Diminishing Table Argument has two conclusions: (1) what we perceive directly and immediately does not have independent existence; and (2) both perceiver-dependent perceptions and perceiver-independent objects exist, where the latter cause and resemble the former. The first conclusion is also drawn from the Double Vision Argument in the Treatise, but the second is not. I consider two interpretations of the Diminishing Table Argument. I find that each interpretation fails to secure much of the second conclusion. I argue that they can be fixed, by paying close attention to the two paragraphs that Hume devotes to describing the effects of natural instinct. In my examination, I find that only the second stage of natural instinct is contradicted by reasoning about perceptual relativity; the first stage remains intact. Upon closer analysis, I find that the effects of the first stage of instinct are described in a manner similar to the effects that "the fancy" produces in the Treatise's description of the philosophical belief. Thus, the Diminishing Table Argument, when supplemented with the effects of the first stage of instinct, preserves the Treatise's insight that reasoning about the phenomenon of perceptual relativity by itself does not entail the double existence of objects and impressions. Then I turn to the broader context of the Diminishing Table Argument: the first "more profound" skeptical objection to the senses. I argue that the skeptical objection proceeds on the assumption (implicitly attributed to philosophers) that instinct and reason are mutually exclusive. But the scientist of human nature may distinguish the effects of instinct. Upon doing so, the scientist sees the fundamental contribution of instinct to any belief, vulgar or philosophical, in external existence.

The Vulgar Belief in Body

What I shall call the "vulgar belief" in the existence of body is the belief that Hume attributes to people who are not engaged in philosophical reflection: this includes non-philosophers at all times, and philosophers when they desist from philosophical reflection. In this section, I compare the accounts of the vulgar belief from the Treatise and Enquiry with regard to (1) origin, (2) psychological strength, (3) content, and (4) the objective situation of the mind (as a scientist of human nature would describe it) in which one entertains this belief. While the Enquiry's discussion of belief in the external world is significantly shorter than the corresponding discussions in the Treatise, I contend that the content and strength of the vulgar belief do not differ between the two texts. It is not clear whether the origin of the vulgar belief differs, but the objective situation remains the same.

First, in the Treatise, Hume claims that the interesting philosophical question is not whether body exists, but what causes our belief in the existence of body. His reason is that the former "is a point, which we must take for granted in all our reasonings" (T 1.4.2.1; SBN 187). Accordingly, in the Treatise Hume engages in a lengthy discussion of the causes of the vulgar belief in body. He argues that the belief is not produced by the senses alone (T 1.4.2.3–13; SBN 188–93) or by any argument about the raw data of sense (T 1.4.2.14; SBN 193). So, he concludes, the belief must be due largely to the contributions of the imagination.⁷ He then engages in what one might call a phenomenological study of the raw data of visual sensation to determine how it might give rise to a belief in continued existence. He finds that those perceptions that are regarded as external existents exhibit constancy or coherence, and he speculates about the imaginative propensities that give rise to the belief in body. These imaginative propensities operate on the data of sense so as to produce belief in one and the same thing's continuing to exist even when the perceiver does not perceive it.⁸ The belief in continued existence "produces" the belief in distinct existence (T 1.4.2.23; SBN 199; cp. T 1.4.2.44; SBN 210), and the belief in external existence comprises both.

The Enquiry's account of the origin of the vulgar belief is significantly shorter than, but not prima facie incompatible with, the Treatise's account. In the Enquiry, Hume describes the vulgar belief as generated by a "blind and powerful instinct of nature" (EHU 12.8; SBN 151), ultimately issuing from men's "natural instinct or prepossession, to repose faith in their senses" (EHU 12.7; SBN 151). There is no further discussion of how the belief is generated, and a fortiori, no complicated discussion of constancy, coherence, or imaginative propensities. But their absence need not amount to a rejection of the account. It does not seem inappropriate to describe fundamental imaginative propensities as "natural instinct or prepossession." Indeed in the Treatise, Hume describes the vulgar belief as the product of "a kind of instinct or natural impulse" (T 1.4.2.51; SBN 214). So Hume may or may not have modified his account of the origin of the vulgar belief.

Secondly, there seems to be a parallel view about the psychological strength of the vulgar belief in both texts. As stated, these imaginative propensities, natural instincts or prepossessions affect all human minds. Psychologically, humans are disposed to adopt the vulgar belief in body. As stated above, "in general all the unthinking and unphilosophical part of mankind, (that is, all of us, at one time or other)" hold the vulgar belief (T 1.4.2.36; SBN 205; cp. T 1.4.2.38; SBN 206). Hume observes:

So strong is the prejudice for the distinct continu'd existence of the former qualities, that when the contrary opinion is advanc'd by modern philosophers, people imagine they can almost refute it from their feeling and experience, and that their very senses contradict this philosophy.

(T 1.4.2.13; SBN 192)

Furthermore,

immediately upon leaving their closets, [philosophers] mingle with the rest of mankind in those exploded opinions, that our perceptions are our only objects, and continue identically and uninterruptedly the same in all their interrupted appearances.

(T 1.4.2.53; SBN 216)

In the Enquiry, Hume calls the vulgar belief the "universal and primary opinion of all men" (EHU 12.9; SBN 152). As we have already noted, this belief is established by natural instinct: "It seems also evident, that, when men follow this blind and powerful instinct of nature, they always suppose the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other" (EHU 12.8; SBN 151; my emphasis). Thus, in both the Treatise and the Enquiry, the vulgar belief, by whatever process it comes to take root, is very compelling and acquires great psychological strength.

This leads to the important third and fourth points of comparison—the content of the vulgar belief and the objective situation (as a scientist of human nature would describe it) in which it is held. In the Treatise, prior to the discussions of constancy and coherence, Hume explicitly analyzes the concept of external existence.⁹ To say that something exists external to a mind or perceiver is to say that that thing meets two conditions. The first is that it continues to exist even when the perceiver does not perceive it; and the second is that it exists distinct from the mind of the perceiver. Distinct existence resolves into two further conditions: first, independent existence, which includes independence of operation from the perceiver; and second, "outness" or being situated outside of the mind of the perceiver (T 1.4.2.2; SBN 188).¹⁰ Hume holds that continued existence implies distinct existence and vice versa (ibid.).

Hume isolates constancy and coherence of our perceptions as the qualities that lead us to believe in the continued existence of objects. His next task is to figure out how exactly the belief in continued existence of objects arises. In what follows, I want to pay particular attention to his description of the content of the vulgar belief. Hume writes:

Now we have already observ'd, that however philosophers may distinguish betwixt the objects and perceptions of the senses; which they suppose co-existent and resembling; yet this is a distinction, which is not comprehended by the generality of mankind, who as they perceive only one being, can never assent to the opinion of a double existence and representation. Those very sensations, which enter by the eye or ear, are with them the true objects, nor can they readily conceive that this pen or paper, which is immediately perceiv'd, represents another, which is different from, but resembling it. In order, therefore, to accommodate myself to their notions, I shall at first suppose, that there is only a single existence, which I shall call indifferently object or perception, according as it shall seem best to suit my purpose, understanding by both of them what any common man means by a hat, or shoe, or stone, or any other impression, convey'd to him by his senses.

(T 1.4.2.31; SBN 202)

Ordinarily, when sensing, people believe that they are in immediate perceptual contact with objects themselves. I see the hat, I smell the shoe, and I feel the stone. It is clear from what Hume writes that he does not attribute the belief in the double existence of objects and perceptions to the vulgar.

Nevertheless, Hume's comment that the "very sensations … are with them the true objects" is initially troublesome. His presentation is a bit infelicitous, in that it potentially misleads the reader to confound the description of the content of the vulgar belief with the objective situation of the vulgar mind.¹¹ That is, the description seems to involve two problematic claims: (1) the vulgar affirm that (certain) perceptions just are objects; and thereby (2) the vulgar adopt a distinction between perceptions and objects. This calls for clarification. The mistake of the first claim is exposed once we distinguish the content of the vulgar belief from its objective situation. As far as content is concerned, the vulgar believe that in sensation they are directly and immediately in contact with hats, shoes, and stones; it is not an image of the stone that I see, but the stone itself. But, observes a scientist of human nature, the objective situation in which people have this belief is one where they are directly acquainted with a perception, not an externally existing object, and in this objective situation, the vulgar believe that what they are directly acquainted with continues to exist independently of them (i.e., it has external existence) (see T 1.4.2.38; SBN 206–7). Hume's point is that the vulgar are not aware that what they regard as hats, shoes, or stones (i.e., objects) are really perceptions. Instead the vulgar think that they perceive hats, shoes, and stones.

But there remains a further problem. There seems to be further confusion about whether and to what extent the vulgar distinguish between objects and perceptions, or external and internal existence. Hume claims that the vulgar do not adopt the philosophical distinction between perceptions and objects. He clearly states, "this is a distinction, which is not comprehended by the generality of mankind" (T 1.4.2.31; SBN 202). But I think it is a mistake to conclude that Hume thinks the vulgar do not draw any distinctions that bear on this subject. The vulgar do not regard all that they perceive as having continued and distinct existence. Consider the following quotation:

[W]e may observe, that there are three different kinds of impressions convey'd by the senses. The first are those of the figure, bulk, motion and solidity of bodies. The second those of colours, tastes, smells, sounds, heat and cold. The third are the pains and pleasures, that arise from the application of objects to our bodies, as by the cutting of our flesh with steel, and such like. Both philosophers and the vulgar suppose the first of these to have a distinct continu'd existence. The vulgar only regard the second as on the same footing. Both philosophers and the vulgar, again, esteem the third to be merely perceptions; and consequently interrupted and dependent beings.

(T 1.4.2.12; SBN 192; cp. T 1.4.2.16; SBN 194)

Again, Hume's description may be problematic, because he is speaking as a scientist of human nature; the vulgar do not describe pleasures and pains as "perceptions" (in the philosophical sense of the term). But it seems clear that Hume thinks that the vulgar (at least implicitly) draw a distinction among things that they are directly acquainted with in perception. In particular, they believe of pleasures and pains that they do not have distinct, continued existence. The pain I sense upon being cut by steel is not a feature of the steel (i.e., it is not the steel's pain), but the cold and figure of the steel are (according to the vulgar) features of the steel itself (cp. T 1.4.2.16; SBN 194). That is, the steel is cold and straight; I feel the steel's coldness. This is tantamount to drawing a rough distinction between "internal" and "external" existence.¹²

Notice, then, that the vulgar belief attributes to hats, shoes, and stones the two conditions for external existence. First, the vulgar believe that stones have continued existence. That is, "[w]hen we are absent from it, we say it still exists, but that we do not feel, we do not see it" (T 1.4.2.38; SBN 207). Second, the vulgar believe that stones have distinct existence. In particular, the stone exists independently of perceivers: it is "neither to be annihilated by our absence, nor to be brought into existence by our presence" (ibid.).

In the Enquiry, Hume again describes the vulgar belief. He writes:

It seems also evident, that, when men follow this blind and powerful instinct of nature, they always suppose the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other. This very table, which we see white, and which we feel hard, is believed to exist, independent of our perception, and to be something external to our mind, which perceives it. Our presence bestows not being on it: Our absence does not annihilate it. It preserves its existence uniform and entire, independent of the situation of intelligent beings, who perceive or contemplate it.

(EHU 12.8; SBN 151–2)

Unlike in the Treatise, Hume does not provide an analysis of the concept of external existence. But he makes clear how the content of the vulgar belief includes the various components of external existence. The vulgar believe that objects have distinct existence. That is, the table exists "independent of our perception" and is believed "to be something external to our mind, which perceives it." These are descriptions of independent existence and "outness," components of distinct existence. The next sentence is nearly verbatim from the Treatise: the perception or object is supposed "neither to be annihilated by our absence, nor to be brought into existence by our presence" (T 1.4.2.38; SBN 207). This implies that the objects continue to exist even when not perceived—their existence is "uniform and entire, independent of the situation of intelligent beings, who perceive or contemplate it."

Furthermore, from Hume's illustration, it is clear that, just as in the Treatise (T 1.4.2.12; SBN 192), the vulgar belief treats the so-called "primary" and "secondary" qualities both as externally existing qualities. The white we see and the hardness we feel are both features of the externally existing table.

Hume retains the infelicitous description of the vulgar belief, inviting conflation of the content with the objective situation. In the quoted passage, he again describes the vulgar as believing "the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other." (Compare to EHU 12.14 (SBN 154): when following the blind, natural instinct, people ordinarily "believe, that the very perception or sensible image is the external object.") Just as with the Treatise, Hume's point is not that the vulgar adopt a distinction between images and objects or that the content of their belief is that images or perceptions have external existence. Instead, the content of the belief is that I see the table itself (i.e., the table exists external to me); and the objective situation is that what is immediately seen is a perception.

Thus, there is not a difference between the Treatise and the Enquiry with respect to the content or strength of the vulgar belief. The vulgar belief is psychologically very compelling, and humans are naturally initially drawn to it. In each text, Hume claims that people ordinarily believe that they sense hats, shoes, stones, and tables directly and immediately. People ordinarily believe that the very thing they sense has continued and distinct existence. Furthermore, people ordinarily consider both so-called primary and secondary qualities as belonging to the external body. If there is a difference in the two accounts, it is with regard to emphasis. In the Treatise, there is greater emphasis on continued existence; whereas in the Enquiry, there is greater emphasis on distinct existence. This difference may be due in part to the longer discussion in the Treatise of the origin of the vulgar belief, with its particular focus on identity. In the Treatise Hume describes imaginative propensities that lead us to mistake successive numerically distinct but resembling perceptions for identical perceptions. Hume claims that these propensities give rise to our belief in the continued existence of what we immediately perceive. He then describes an argument that philosophers use to expose the falsity of the vulgar belief. As we shall see, the argument fundamentally turns on distinct existence. Since Hume omits the complicated psychological account in the Enquiry but retains the argument against the vulgar belief, we can thus account for the greater emphasis on distinct existence.

Furthermore, there is not a significant difference in the broad strokes of Hume's descriptions of the objective situation that corresponds to the vulgar belief. In each account from the Treatise and the Enquiry, in sensation the vulgar are directly in contact with perceptions. And, according to Hume as scientist of human nature, it is an impression or image to which external existence is attributed. Of course, in the Treatise, Hume goes to great lengths to describe the features of the perceptions in virtue of which we attribute external existence; but the overall similarity between the Treatise and the Enquiry remains: in reality it is a perception that the vulgar believe to exist externally.

The Treatise's Account of the Philosophical Rejection of the Vulgar Belief

In the Treatise, Hume claims that "a very little reflection and philosophy is sufficient to make us perceive the fallacy of that (viz. vulgar) opinion" (T 1.4.2.44; SBN 210; cp. EHU 12.9; SBN 152). In each text, Hume describes the vulgar belief as "false," "erroneous," or "contrary to reason" (see T 1.4.2.43, 48; SBN 209, 213; and EHU 12.10, 16; SBN 152, 155).¹³ In each, Hume describes an argument that draws upon the phenomenon of perceptual relativity. But a difference occurs in the two accounts. In the Treatise, Hume claims that the perceptual relativity argument shows only that what we perceive (i.e., impressions or ideas) does not have continued existence; philosophical invention is required to get to the double existence of enduring objects and perceptions. In contrast, in the Enquiry, the conclusion of the perceptual relativity argument is both (1) the falsity of the vulgar belief in the external existence of what we perceive; and (2) the double existence of perceptions and objects. In this section, I examine the Treatise's argument against the vulgar belief; in the next section, I turn to the Enquiry's argument.

In the Treatise, Hume traces how our natural imaginative propensities lead us to believe in the continued existence of certain perceptions. Once continued existence is established, the mind unreflectively adds distinct existence (T 1.4.2.44; SBN 210). Hume seeks to describe "experiments" which would show that "the doctrine of the independent existence of our sensible perceptions is contrary to the plainest experience" (ibid.). This experiment and its conclusion are the Double Vision Argument (hereafter "DVA"):

'Twill first be proper to observe a few of those experiments, which convince us, that our perceptions are not possest of any independent existence. When we press one eye with a finger, we immediately perceive all the objects to become double, and one half of them to be remov'd from their common and natural position. But as we do not attribute a continu'd existence to both these perceptions, and as they are both of the same nature, we clearly perceive, that all our perceptions are dependent on our organs, and the disposition of our nerves and animal spirits. This opinion is confirm'd by the seeming encrease and diminution of objects, according to their distance; by the apparent alterations in their figure; by the changes in their colour and other qualities from our sickness and distempers; and by an infinite number of other experiments of the same kind; from all which we learn, that our sensible perceptions are not possest of any distinct or independent existence.

(T 1.4.2.45; SBN 210–1)

This argument is designed to show that perceptions of sense are partially causally dependent on percipients' bodily states and therefore do not have distinct existence. When my eyes are crossed, I see (for example) two tables instead of just one. In such a circumstance, the vulgar do not hold that both tables will continue to exist when not perceived; instead, they believe that one table will cease to exist when my eyes are uncrossed. That is, the vulgar belief does not attribute continued existence to both tables. But both tables are "of the same nature."¹⁴ That is, both tables are to be regarded as like effects. Because like effects imply like causes, the other table also lacks continued existence. Since distinct existence implies continued existence, neither table operates independently of percipients.¹⁵ Moreover, the perceptions of double vision are of the same nature as all other visual perceptions. So all visual perceptions lack independent existence. There is nothing special about double vision; other visually relative phenomena would suffice to establish this point. Further, similar arguments can be offered for other sensory modalities. Thus all sense perceptions are causally dependent upon the bodily states of percipients, and therefore none of them has distinct existence.¹⁶

James Somerville argues that DVA targets a philosophical view about the status of our perceptions, not the vulgar belief that what they feel and see are hats, shoes, stones, and tables.¹⁷ Earlier, I distinguished the content of the vulgar belief from the objective situation. The content is that the vulgar believe that they see and feel tables, and the objective situation in which they hold this belief is one where they attribute external existence to perceptions. Somerville's point, then, is that DVA attacks only the objective situation, not the content of the belief. Notice, however, that the argument is also conducted at the level of the content of the belief. The crucial premises are "we do not attribute a continu'd existence to both these perceptions" and "they are both of the same nature." The former is a claim about the vulgar response to the phenomenon of double vision and the latter is a phenomenological claim. The upshot is that the argument brings the content in line with the objective situation; the falsity of the vulgar belief is exposed.

Hume comments,

The natural consequence of this reasoning shou'd be, that our perceptions have no more a continu'd than an independent existence; and indeed philosophers have so far run into this opinion, that they change their system, and distinguish, (as we shall do for the future) betwixt perceptions and objects, of which the former are suppos'd to be interrupted, and perishing, and different at every different return; the latter to be uninterrupted, and to preserve a continu'd existence and identity.

(T 1.4.2.46; SBN 211)

Upon examining the philosophical belief more closely, Hume finds that it depends upon part of the vulgar belief, viz. the conviction that something has external existence. Since DVA shows that it is wrong to attribute continued and distinct existence to perceptions, philosophers invent the category of objects. Perceptions are perceiver-dependent; objects are perceiver-independent. Hume calls this philosophical view "the opinion of a double existence" (T 1.4.2.31, 52; SBN 202, 216; cp. T 1.4.2.46; SBN 211), because it posits the dual existence and correspondence of objects and perceptions. (Throughout this paper I shall refer to this view as the "double existence theory" or "double existence view.") In various places Hume states the double existence theory. In his minimal descriptions of it, he claims that it involves a Derivation Thesis: perceptions are caused by objects. (See, e.g., T 1.4.2.46, 52, 14; SBN 211, 215, 193.) But frequently he adds some additional relationship between perceptions and objects, such as resemblance or representation. (See, e.g., T 1.4.2.48, 54–5, 4; SBN 213, 216–7, 189; see also EHU 12.9, SBN 152, reprinted above, where Hume describes perceptions as "fleeting copies or representations of other existences," allowing for either resemblance or mere representation.)¹⁸

But, Hume remarks, the philosophical view "has no primary recommendation either to reason or the imagination, but acquires all its influence on the imagination from the [vulgar belief]" (T 1.4.2.46; SBN 211). We cannot reason straightaway from the existence of our perceptions to the existence of objects. This is because objects are in principle unobservable, and therefore we can never observe "a conjunction or a relation of cause and effect" between perceptions and objects (T 1.4.2.47; SBN 212). Secondly, our natural imaginative propensities initially lead us to adopt the vulgar belief, not the double existence view (T 1.4.2.48; SBN 212–3). Thus the philosophical belief in double existence fundamentally depends upon the vulgar belief for its development.

How does the philosophical belief depend upon the vulgar belief? After showing, from perceptual relativity, that the vulgar belief in the continued and distinct existence of what we immediately perceive is false,

'twou'd naturally be expected, that we must altogether reject the opinion, that there is such a thing in nature as a continu'd existence, which is preserv'd even when it no longer appears to the senses. The case, however, is otherwise. Philosophers are so far from rejecting the opinion of a continu'd existence upon rejecting that of the independence and continuance of our sensible perceptions, that tho' all sects agree in the latter sentiment, the former, which is, in a manner, its necessary consequence, has been peculiar to a few extravagant sceptics; who after all maintain'd that opinion in words only, and were never able to bring themselves sincerely to believe it.

(T 1.4.2.50; SBN 214)

The fundamental imaginative conviction that something has continued existence proves too strong to be overturned by philosophical reflection.

Thus tho' we clearly perceive the dependence and interruption of our perceptions, we stop short in our career, and never upon that account reject the notion of an independent and continu'd existence. That opinion has taken such deep root in the imagination, that 'tis impossible ever to eradicate it, nor will any strain'd metaphysical conviction of the dependence of our perceptions be sufficient for that purpose.

(T 1.4.2.51; SBN 214)

The important point for the present purpose is that the double existence theory is not a straightforward implication of DVA. Instead, it is a philosophical "fiction" (T 1.4.2.52; SBN 215) that philosophers "invent" (T 1.4.2.56; SBN 218).¹⁹ Briefly, the mind is pulled in two directions by the imagination and by reason. The imagination is convinced, by the very propensities that initially produce the vulgar belief, that something has continued and distinct existence. But reason (i.e., causal reasoning about perceptual relativity) points out that perceptions are not fit candidates for distinct or continued existence. So the philosophical hypothesis is an attempt to satisfy both demands. With the invention of the new category of objects, philosophers aim to satisfy the imagination by positing something that has continued existence, and simultaneously aim to satisfy reason by not attributing continued existence to perceptions (T 1.4.2.50, SBN 213–4; cp. T 1.4.2.52; SBN 215–6).

Furthermore, the belief that perceptions resemble their ancestral objects is due to further effects of the imagination. Hume writes,

I have already shown, that the relation of cause and effect can never afford us any just conclusion from the existence or qualities of our perceptions to the existence of external continu'd objects; And I shall farther add, that even tho' they cou'd afford such a conclusion, we shou'd never have any reason to infer, that our objects resemble our perceptions. That opinion, therefore, is deriv'd from nothing but the quality of the fancy above-explain'd, that it borrows all its ideas from some precedent perceptions. We never can conceive any thing but perceptions, and therefore must make every thing resemble them.

(T 1.4.2.54; SBN 216)

Philosophers do not simply believe that objects in general resemble perceptions. Rather, philosophers hold that each perception resembles the object that caused it. This, Hume claims, is due to the psychological propensity to "compleat the union": once the ideas of perception and object are related "in the fancy" by causation, we are disposed to add the relation of resemblance (T 1.4.2.55; SBN 217). The point is that philosophers' beliefs about resemblance between objects and perceptions are due to the effects of imaginative propensities.

The Enquiry's Account of the Philosophical Rejection of the Vulgar Belief

In the Enquiry, Hume takes up the topic of skepticism with regard to the senses in the first part of the final section, "Of the Academical or Sceptical Philosophy." In the second part, he examines popular and philosophical challenges to reason, and in the third part he recommends mitigated skepticism over the extreme Pyrrhonism that he considers in the preceding parts. My focus here is on the first part.

Hume divides skepticisms into two kinds: those that are "antecedent to all study and philosophy" (EHU 12.3; SBN 149) and those that are "consequent to science and enquiry" (EHU 12.5; SBN 150). The sort of arguments that we are considering here fall into the latter category, since the skeptical doubt arises only after some observations or argument. In this category, Hume distinguishes "trite topics" which are easily dismissed, and "more profound arguments against the senses, which admit not of so easy a solution" (EHU 12.6; SBN 151).

Somerville points out that the phenomena of diminishing apparent magnitude and double vision are included among the "trite topics" that Hume dismisses.²⁰ Hume writes:

I need not insist upon the more trite topics, employed by the sceptics in all ages, against the evidence of sense; such as those which are derived from the imperfection and fallaciousness of our organs, on numberless occasions; the crooked appearance of an oar in water; the various aspects of objects, according to their different distances; the double images which arise from the pressing one eye; with many other appearances of a like nature. These sceptical topics, indeed, are only sufficient to prove, that the senses alone are not implicitly to be depended on; but that we must correct their evidence by reason, and by considerations, derived from the nature of the medium, the distance of the object, and the disposition of the organ, in order to render them, within their sphere, the proper criteria of truth and falsehood. There are other more profound arguments against the senses, which admit not of so easy a solution.

(EHU 12.6; SBN 151)

In this passage, Hume has the following kind of example in mind. When I am shopping for socks at the store under fluorescent lights, I may wonder whether the particular pair that I hold is navy blue or black.²¹ But from my failing to know which color the socks are on the basis of sense perception alone, it does not follow that my senses are not to be trusted at all. Instead, I am able to recognize that the apparent color of the socks is in part a function of the effect of the store's fluorescent lights. With that in mind, I can take measures to adjust my judgment about the color of the socks (e.g., compare them to a known black object or buy them and look at them in other lighting).

So while Hume mentions double vision in particular, the kind of worry raised by the "trite topics" is not the same problem generated by DVA. Instead, DVA raises a problem concerning the vulgar belief in the continued and distinct existence of what I immediately perceive. If I take into consideration "the nature of the medium, the distance of the object, and the disposition of the organ," this does not affect DVA's conclusion that sense perceptions do not have distinct or continued existence. For whether I am healthy or not, whether I look through water or air, or whether I approach or remove from an object, what I am directly and immediately acquainted with is causally dependent on my sensory organs. Moreover, as Hume argues in the Treatise, the senses do not provide any evidence in favor of or against continued existence (T 1.4.2.3; SBN 188–9). So they cannot deceive us with regard to continued existence. Thus it would not be possible to "correct their (viz. the senses') evidence by reason" (EHU 12.6; SBN 151) precisely because they offer no such evidence.²²

The philosophical rejection of the vulgar belief in body is part of the "more profound arguments against the senses, which admit not of so easy a solution" (ibid.). The skeptical dilemma that Hume ultimately describes is that belief in external existence "if rested on natural instinct, is contrary to reason, and if referred to reason, is contrary to natural instinct, and at the same time carries no rational evidence with it, to convince an impartial enquirer" (EHU 12.16; SBN 155). To this end, Hume describes the Diminishing Table Argument (hereafter "DTA"), that aims to show the falsity of the belief "rested on natural instinct." He writes:

But this universal and primary opinion of all men is soon destroyed by the slightest philosophy, which teaches us, that nothing can ever be present to the mind but an image or perception, and that the senses are only the inlets, through which these images are conveyed, without being able to produce any immediate intercourse between the mind and the object. The table, which we see, seems to diminish, as we remove farther from it: But the real table, which exists independent of us, suffers no alteration: It was, therefore, nothing but its image, which was present to the mind. These are the obvious dictates of reason; and no man, who reflects, ever doubted, that the existences, which we consider, when we say, this house and that tree, are nothing but perceptions in the mind, and fleeting copies or representations of other existences, which remain uniform and independent.

(EHU 12.9; 152)

There are similarities and differences between DVA and DTA. The phenomena that they describe are visual, and among their conclusions, both arguments include that what we directly and immediately perceive does not have external existence (i.e., that the vulgar belief is false). However, there are differences. For one, DTA uses only the phenomenon of diminishing visual magnitude as we move farther away from the table, whereas DVA uses the phenomenon of double vision, although "the seeming encrease and diminution of objects, according to their distance" is mentioned as another example (T 1.4.2.45; SBN 211). Further, only DTA purports to establish straightaway the double existence of the real table and its image that we see.

It is this last point that is puzzling. Hume insists in the Treatise that the double existence theory is not a logical consequence of DVA; instead, it is a philosophical invention, aimed at satisfying the psychological compulsion to attribute continued (and distinct) existence to something related to perception. And the belief in resemblance between object and perception is due to further imaginative propensities. How can a different instance of perceptual relativity yield the double existence theory as its conclusion?

To begin, my claim that DTA draws two conclusions straightaway from the phenomenon of perceptual relativity requires defense. The first conclusion, which I shall call the "Dependence Conclusion," states that, contrary to the vulgar belief, what I perceive directly and immediately does not have independent or external existence. In the passage quoted above, Hume writes that philosophy "teaches us, that nothing can ever be present to the mind but an image or perception." In the same passage Hume also writes, "no man, who reflects, ever doubted, that the existences, which we consider, when we say, this house and that tree, are nothing but perceptions in the mind, and fleeting copies or representations of other existences." These statements directly oppose the vulgar belief that that which I directly and immediately perceive "would exist, though we and every sensible creature were absent or annihilated" (EHU 12.7; SBN 151). Moreover, the second statement also comments on the duration of the perception: it is fleeting.²³ Again, the vulgar belief holds that what I directly and immediately perceive "preserves its existence uniform and entire, independent of the situation of intelligent beings, who perceive or contemplate it" (EHU 12.8; SBN 152). But this argument concludes that what I perceive is a perception, and as a perception it is fleeting.

How does DTA purport to establish the Dependence Conclusion? At one vantage point, what I directly and immediately perceive is one size; at another vantage point, it is another size. In this scenario, only I have changed; the externally existing table is supposed not to have suffered any alteration. So the externally existing table could not have each size at different times. Therefore, what I directly and immediately perceive is not an externally existing table. As external existence involves continued and distinct existence, the Dependence Conclusion states that what I directly and immediately perceive has neither continued nor distinct existence.

The second conclusion is what I shall call the "Double Existence Conclusion," according to which there exist objects over and above perceptions, and perceptions resemble their ancestral objects. In the passage quoted above, Hume observes that the "table" we directly and immediately perceive

was, therefore, nothing but its image, which was present to the mind. These are the obvious dictates of reason; and no man, who reflects, ever doubted, that the existences, which we consider, when we say, this house and that tree, are nothing but perceptions in the mind, and fleeting copies or representations of other existences, which remain uniform and independent.

(EHU 12.9; SBN 152; my emphasis)

DTA concludes from perceptual relativity that the visual perception of the table is caused by and resembles an externally existing table. One might try to hold that the representational thesis is tacked on at the end, as one of the "obvious dictates of reason."²⁴ But it seems clear that the possessive pronoun "its" in the description of the perception ("its image") is intended to refer to the externally existing table. So the phenomenon of perceptual relativity is somehow supposed to lead to the conclusion that there exist perceiver-independent objects over and above perceiver-dependent perceptions, where the latter are caused by and resemble the former.

The question, then, is how does DTA purport to establish the Double Existence Conclusion? There are certain constraints on a suitable interpretation. Hume holds in the Treatise that reasoning about perceptually relative phenomena does not suffice to establish the double existence theory. So either an additional premise will have to be found, or some account of why Hume changes his mind from the Treatise to the Enquiry will have to be offered.

The Rationally Realist Interpretation

A natural interpretation is that DTA purports to establish the existence of perceptions over and above objects simply from reasoning about perception. I shall designate it the "Rationally Realist Interpretation" because it treats the realist commitment to both perceptions and objects as entirely (or primarily) a logical consequence of the phenomenon of perceptual relativity; that is, the Double Existence Conclusion is reached by reasoning alone from observations about perception (i.e., without the intervention of imagination). This interpretation has been adopted by both John P. Wright and Georges Dicker.²⁵ Let's consider Dicker's formulation:

1. 1. When we look at an object from different distances and angles, what we see changes.

2. 2. When we look at an object from different distances and angles, the object itself does not change.

∴ (3) When we look at an object from different distances and angles, what we see is something other than the object itself—an impression, image, or sense-datum.²⁶

The Rationally Realist Interpretation of DTA begins with the premise that there exists an external table. As an external table, it continues to exist when not perceived and exists distinct from minds that perceive it. Thus a change that takes place only in the perceiver will not alter the table at all. When a perceiver removes from the table, the external table does not shrink. Nevertheless, what the perceiver sees appears smaller. Therefore it is contradictory to identify the external table with what the perceiver sees. So there exist two tables: the external table and the table that changes size when the perceiver moves. In the terminology that I have introduced, the Rationally Realist Interpretation establishes the Dependence Conclusion by concluding that what is seen changes when there are changes to the percipient; and this interpretation establishes part of the Double Existence Conclusion, by affirming that there exist two tables: the external table and the table that is seen. It is not clear how this interpretation yields the rest of the Double Existence Conclusion (that perceptions are (partially) caused by and resemble their ancestral objects). Perhaps on Dicker's formulation, to say that I "look at an (external) object" guarantees that what I see is related to the external object, even when it is shown that what I see is not the external object but a perception. Alternatively, an argument to the best explanation might be offered to establish that the perception is (partially) caused by and resembles the external table.

Although he grants that the argument is valid, Dicker objects to its soundness, arguing that the first premise is false. It commits the Sense-Datum Fallacy, by reifying that which we see. Dicker claims that all the observation about perception warrants is a weaker premise:

1. 1a. When we look at an object from different distances and angles, the object's size and shape seem to change.²⁷

Indeed, Hume's language is suggestive of premise (1a) rather than (1): "The table, which we see, seems to diminish, as we remove farther from it" (EHU 12.9; SBN 152; my emphasis). As Thomas Reid argues, once one makes a distinction between apparent and real magnitude, the sophism in the argument becomes clear: one and the same external table may have changing apparent magnitudes and an unchanging real magnitude.²⁸

Dicker and Reid think that the argument, interpreted with unmodified premise (1) above, is unsound. Wright tries to defend the argument against this criticism.²⁹ Wright distinguishes between changes in the intrinsic properties and changes in the extrinsic properties of an object. He argues that the observed change is in intrinsic properties (change in size) whereas the external table changes in extrinsic properties (change in apparent magnitude relative to the observer). So the external table cannot be what is seen, because it does not undergo the appropriate kind of change. This defense would not be compelling to Dicker or Reid, because it presupposes exactly what they want to deny: that there exists something that undergoes change in exactly the manner we perceive.

The most distinctive feature of the Rationally Realist Interpretation in general is that it begins with the premise that an external table exists. On this interpretation, DTA does not proceed as a reductio of the vulgar belief—assuming that we are directly acquainted with an external table, only to show that it is not an external table, but a perception. Instead, on this interpretation of DTA, the existence of an external table is not challenged. Several commentators see this as a problematic premise.³⁰ Their point is that once it is shown that we are directly and immediately acquainted only with perceptions, the premise that there is an external table becomes questionable. Furthermore, once our knowledge of the existence of an external table is doubted, it is difficult to see how to conclude that objects cause and resemble perceptions.

Clearly there are many complicated philosophical issues that DTA, so interpreted, raises. What matters for our purposes is the appropriateness of this as an interpretation of DTA. That is, we might still wonder whether this interpretation can preserve the parallel structure between the Treatise and the Enquiry. So how does this interpretation require us to understand DVA?³¹ Again, the premise that there exists an external object would not be an assumption for the sake of a reductio; it would be a given premise. What is shown, through the example of double vision, is that what is directly and immediately seen is not an external object. But, just as with DTA, that would leave untouched the premise that there is an external object. This would make it possible to draw the Double Existence Conclusion straightaway from DVA as well.

The trouble with this line of interpretation is that it sits poorly with Hume's comment about the scope of DVA: the phenomenon of perceptual relativity suffices to show only that what we directly and immediately perceive (viz., perceptions) do not have external existence. Instead, the philosophical double existence hypothesis arises from imaginative invention. So the Rationally Realist Interpretation of DTA requires us to interpret Hume as having changed his mind about the logical consequences of perceptual relativity. Furthermore, the Rationally Realist Interpretation (of DTA or DVA) leaves unexplained why we should grant that there is an external object.

The Reductio of the Vulgar Belief Interpretation

Given the problems with the Rationally Realist Interpretation, perhaps it would be better to treat the premise that there exists an external object not as a given, but as an assumption for the sake of a reductio ad absurdum of the vulgar belief.³² Let's call this interpretation the "Reductio of the Vulgar Belief Interpretation." Thus, let's assume (for the sake of a reductio) that the vulgar belief is true: what I am directly and immediately acquainted with in perception are themselves external objects. For example, when looking at a table, the vulgar belief holds that what I directly and immediately see is an external table. As an external table, it continues to exist when I do not perceive it and operates independently of my observation. But when I remove from the table, what I directly and immediately see shrinks. If what I directly and immediately see were an external table, it would not diminish in size. The contradiction is thus elicited: the immediately and directly sensed table both shrinks (as I observe) and does not shrink (as must happen if it is an external table). Therefore the assumption was false; what I directly and immediately see is not an external table.

Thus the Reductio Interpretation establishes the Dependence Conclusion, by showing that the vulgar belief is false; that is, it is not the case that what I directly and immediately see has external existence. There is nothing in this conclusion that helps to establish any part of the Double Existence Conclusion; on this interpretation, there is no independent commitment to the existence of something external. In this regard, this interpretation of DTA does not conclude from the phenomenon of perceptual relativity any more than the Treatise's DVA. Hence as an interpretation of the diminishing table passage, this interpretation fails to account for the Double Existence Conclusion that is stated. So unless we bolster the argument with additional premises, it is not a complete interpretation of DTA.

Natural Instinct's Supplemental Premises

So far, we have considered two interpretations that regard the diminishing table passage as an argument. In the Rationally Realist Interpretation, the argument moves from the existence of external objects to the conclusion that perceptions also exist. This interpretation was found wanting in that the argument, if successful, seems to render questionable the premise that external objects exist, and does not explicitly indicate why we should conclude that objects cause or resemble perceptions. This interpretation also seems to hold that the double existence of objects and perceptions may be deduced directly from the phenomenon of perceptual relativity, contrary to Hume's explicit discussion following DVA. In contrast, the Reductio Interpretation shows only the falsity of the vulgar belief that what we directly and immediately perceive has continued and distinct existence. In this limited conclusion it is similar to DVA. But its problem is that it fails to reach the conclusions that objects exist and, a fortiori, that they resemble the perceptions they cause. To reach those conclusions, other premises need to be added. But there are no more premises in the passage about the diminishing table.

In this section, I describe a supplement to either of these interpretations. As I argue, natural instinct provides the basis for thinking that external objects exist. Thus it modifies the Rationally Realist Interpretation, by introducing independent instinctive grounds for thinking that external objects exist;³³ and it fills the lacuna in the Reductio Interpretation, introducing the category of external objects. Further, I argue that natural instinct also moves philosophers to think that objects cause and resemble perceptions. In support, I examine the Treatise's discussion of the formation of the philosophical system from the vulgar belief. I argue that the Enquiry's description of the effects of natural instinct retains the essential elements of the Treatise's account.

If we search the paragraphs preceding DTA, we find that Hume uses two paragraphs to describe instinct's contribution to the development of the vulgar belief. He breaks the story down into two stages.³⁴ First:

It seems evident, that men are carried, by a natural instinct or prepossession, to repose faith in their senses; and that, without any reasoning, or even almost before the use of reason, we always suppose an external universe, which depends not on our perception, but would exist, though we and every sensible creature were absent or annihilated.

(EHU 12.7; SBN 151)

Hume continues:

It seems also evident, that, when men follow this blind and powerful instinct of nature, they always suppose the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other.

(EHU 12.8; SBN 151)

The first stage establishes the instinctive belief that something has external existence. The second stage goes beyond the first stage, and attributes external existence to certain perceptions. This second stage is the objective situation of the vulgar belief, and it is contradicted by the Dependence Conclusion.

But what about the first stage? At a minimum, it contributes the conviction that something has external (i.e., distinct and continued) existence: "we always suppose an external universe, which depends not on our perception, but would exist, though we and every sensible creature were absent or annihilated" (EHU 12.7; SBN 151). If we add this premise to the Reductio Interpretation, we get part of the Double Existence Conclusion: since perceptions do not have external existence, there must exist something else that does—let's call these external things objects.³⁵ In this respect, this is not significantly different from the Treatise's account of how the philosophical hypothesis is developed. Recall, in the Treatise, Hume claims that the conclusion of DVA should be that perceptions do not have external existence. But the vulgar conviction that something has external existence persists; and philosophers yield to both demands, attributing uninterruptedness, identity, and externality to objects, and interruptedness, difference, and perceiver-dependence to perceptions (T 1.4.2.51–2; SBN 214–6).

But this is not all of DTA's Double Existence Conclusion. There are the further claims that objects cause and resemble perceptions. To see how instinct contributes these, let's examine more closely the first stage of instinct. Recall that Hume writes:

It seems evident, that men are carried, by a natural instinct or prepossession, to repose faith in their senses; and that, without any reasoning, or even almost before the use of reason, we always suppose an external universe, which depends not on our perception, but would exist, though we and every sensible creature were absent or annihilated.

(EHU 12.7; SBN 151)

In this sentence, Hume describes the effects of instinct in two clauses: the first states that men "repose faith in their senses"; the second states that we "suppose an external universe." What is the relation between these?

We might try to interpret "faith in [our] senses" as acceptance of the raw data of our senses. But the senses alone contribute little to our belief in external existence. As Hume argues in the Treatise, our senses alone do not represent anything as external:

Thus to resume what I have said concerning the senses; they give us no notion of continu'd existence, because they cannot operate beyond the extent, in which they really operate. They as little produce the opinion of a distinct existence, because they neither can offer it to the mind as represented, nor as original. To offer it as represented, they must present both an object and an image. To make it appear as original, they must convey a falshood; and this falshood must lie in the relations and situation: In order to which they must be able to compare the object with ourselves; and even in that case they do not, nor is it possible they shou'd, deceive us. We may, therefore, conclude with certainty, that the opinion of a continu'd and of a distinct existence never arises from the senses.

(T 1.4.2.11; SBN 191–2)

Our senses do not present anything as continued or distinct; thus they do not present anything as existing externally. In the next two paragraphs in the Treatise, Hume "confirm[s]" this point, by comparing the (modern) philosophical and vulgar views about the various sensory impressions: the so-called primary qualities, the so-called secondary qualities, and hedonic sensations. Philosophers distinguish primary from secondary qualities, where the former are external qualities but the latter are merely perceptions. The vulgar, however, think that both solidity and cold are features of the (externally existing) steel, and think that their experience refutes the philosophical distinction.³⁶ But they also think that pain is not a feature of the steel. Philosophers, on the other hand, point out that both the cold and the pain are "nothing but perceptions arising from the particular configurations and motions of the parts of the body" (T 1.4.2.13; SBN 192–3). From these conflicting opinions about the various impressions of sense, Hume concludes, "that as far as the senses are judges, all perceptions are the same in the manner of their existence" (T 1.4.2.13; SBN 193).

Since the senses alone do not produce the belief in external existence, "faith in [our] senses" should not be understood as concerning only the raw data of the senses. Instead, I contend, it includes (unreflective) acceptance of the effects of the fundamental imaginative propensities or instincts that operate on the raw data of the senses. One notable effect of instinct is the belief that something external exists. (So "faith in [our] senses" includes, but is not equivalent to, the belief that something external exists.) To show this, I examine the corresponding passages in the Treatise where Hume explains how the philosophical system depends upon the vulgar belief. I contend that the Enquiry's account does not differ from the Treatise's account of the development of the philosophical system out of the "struggle" between reason and the imagination. Thus the instinctive "faith in [our] senses" generates the causal and resemblance components of the philosophical belief in the double existence of objects and perceptions.

In the Treatise, Hume contrasts the philosophical opinion, which "we form after a calm and profound reflection," and the vulgar belief, which "we embrace by a kind of instinct or natural impulse" (T 1.4.2.51; SBN 214). (Notice that Hume describes the vulgar belief as deriving from a kind of instinct.) Hume observes,

If these opinions become contrary, 'tis not difficult to foresee which of them will have the advantage. As long as our attention is bent upon the subject, the philosophical and study'd principle may prevail; but the moment we relax our thoughts, nature will display herself, and draw us back to our former opinion. Nay she has sometimes such an influence, that she can stop our progress, even in the midst of our most profound reflections, and keep us from running on with all the consequences of any philosophical opinion. Thus tho' we clearly perceive the dependence and interruption of our perceptions, we stop short in our career, and never upon that account reject the notion of an independent and continu'd existence. That opinion has taken such deep root in the imagination, that 'tis impossible ever to eradicate it, nor will any strain'd metaphysical conviction of the dependence of our perceptions be sufficient for that purpose.

(T 1.4.2.51; SBN 214)

When reason and the imagination are opposed, reason can never secure a complete, lasting victory. Even if reason were to contradict the imagination entirely, reason's victory would be temporary, because reason's conclusion could not be sustained completely without considerable effort and this effort could not be exerted for long. (This is why Hume says that the vulgar belief is held by non-philosophers at all times, and philosophers when they desist from philosophical reflection. See T 1.4.2.36, 38, 53; SBN 205, 206, 216.) However, it is possible for reason to carry out its inferences to a limited degree, while the imagination pulls in the opposite direction. Hume describes this as involving "some struggle and opposition" whose reconciliation is reached by the double existence theory:

This philosophical system, therefore, is the monstrous offspring of two principles, which are contrary to each other, which are both at once embrac'd by the mind, and which are unable mutually to destroy each other. The imagination tells us, that our resembling perceptions have a continu'd and uninterrupted existence, and are not annihilated by their absence. Reflection tells us, that even our resembling perceptions are interrupted in their existence, and different from each other. The contradiction betwixt these opinions we elude by a new fiction, which is conformable to the hypotheses both of reflection and fancy, by ascribing these contrary qualities to different existences; the interruption to perceptions, and the continuance to objects. Nature is obstinate, and will not quit the field, however strongly attack'd by reason; and at the same time reason is so clear in the point, that there is no possibility of disguising her. Not being able to reconcile these two enemies, we endeavour to set ourselves at ease as much as possible, by successively granting to each whatever it demands, and by feigning a double existence, where each may find something, that has all the conditions it desires.

(T 1.4.2.52; SBN 215)

On Hume's account, reason convinces us to deny that perceptions are identical, uninterrupted, and continuous. But the imagination persists in holding that something related to perception continues to exist. As we have seen, reason cannot successfully overthrow the imaginative conviction; so it is not possible to claim simply that nothing related to perception has continued existence (cp. T 1.4.2.50; SBN 214). Thus, philosophers introduce a distinction in order to satisfy both of these convictions: perceptions are dependent, interrupted, and different, whereas objects are independent, continued, and identical.

Hume is not entirely clear about how the imagination leads philosophers to conclude that objects cause perceptions. (Again, we should recall the earlier discussion that neither the senses alone nor reason alone is the source of the belief in continued or distinct existence (T 1.4.2.3–14; SBN 188–93).) It may be the case that because the philosophical imagination is led to posit the existence of objects upon thinking about perceptions, an association is developed between the ideas of objects and perceptions, which the imagination confounds with causation. In any case, Hume is clear that reason does not directly support this conclusion:

The only existences, of which we are certain, are perceptions, which being immediately present to us by consciousness, command our strongest assent, and are the first foundation of all our conclusions. The only conclusion we can draw from the existence of one thing to that of another, is by means of the relation of cause and effect, which shows, that there is a connexion betwixt them, and that the existence of one is dependent on that of the other. The idea of this relation is deriv'd from past experience, by which we find, that two beings are constantly conjoin'd together, and are always present at once to the mind. But as no beings are ever present to the mind but perceptions; it follows that we may observe a conjunction or a relation of cause and effect betwixt different perceptions, but can never observe it betwixt perceptions and objects. 'Tis impossible, therefore, that from the existence or any of the qualities of the former, we can ever form any conclusion concerning the existence of the latter, or ever satisfy our reason in this particular.

(T 1.4.2.47; SBN 212)

We cannot establish by direct causal reasoning that there is a causal relationship between objects and perceptions, because we can never observe the conjunction of perceptions and objects—because objects are in principle unobservable. Fred Wilson points out that Hume's criticism excludes only direct causal reasoning. However, perhaps the philosopher could pursue some kind of indirect causal argument, by appeal to causal principles, such as every event has a cause and same effects have the same causes.³⁷ In such an argument, we would conclude that our perceptually relative perceptions have causes, but other perceptions are inadequate for the task, because they lack continued or distinct existence. Therefore something else that has these qualities causes our perceptions. On such an interpretation, reason cooperates with the imagination, by directing the conviction in continued existence to invent the cause of our dependent and interrupted perceptions.

The belief in resemblance receives more explicit treatment, as being a "very conspicuous" effect of "the fancy":

First, We suppose external objects to resemble internal perceptions. I have already shown, that the relation of cause and effect can never afford us any just conclusion from the existence or qualities of our perceptions to the existence of external continu'd objects; And I shall farther add, that even tho' they cou'd afford such a conclusion, we shou'd never have any reason to infer, that our objects resemble our perceptions. That opinion, therefore, is deriv'd from nothing but the quality of the fancy above-explain'd, that it borrows all its ideas from some precedent perceptions. We never can conceive any thing but perceptions, and therefore must make every thing resemble them.

(T 1.4.2.54; SBN 216)

Hume continues:

Secondly, As we suppose our objects in general to resemble our perceptions, so we take it for granted, that every particular object resembles that perception, which it causes. The relation of cause and effect determines us to join the other of resemblance; and the ideas of these existences being already united together in the fancy by the former relation, we naturally add the latter to compleat the union. We have a strong propensity to compleat every union by joining new relations to those which we have before observ'd betwixt any ideas, as we shall have occasion to observe presently.

(T 1.4.2.55; SBN 217)

The second quotation makes clear the order of the development of the Double Existence Conclusion: first, philosophers believe that objects cause perceptions, and second, philosophers believe that objects resemble perceptions. Just as with causation, the belief in resemblance arises not because philosophers observe objects directly and compare them to their perceptions; objects are in principle unobservable. Instead, the belief in resemblance arises because of the limits of conceivability: the fancy "borrows all its ideas from some precedent perceptions." We cannot conceive of something different in kind from perceptions.³⁸ So the qualities that are attributed to objects are qualities that perceptions have. Furthermore, as Hume observes in the second paragraph, philosophers are inclined to make objects resemble the particular perceptions they cause. (Again, reason can "cooperate" with imagination, in excluding certain qualities from objects when it is shown that objects cannot have such qualities. For example, such reasoning might form the basis for the primary-secondary quality distinction. Hume's point here is that reasoning by itself would never lead us to think that objects resemble our perceptions.) He explains that this belief that objects resemble the perceptions they cause is due to the imaginative propensity to "compleat the union."

Thus, in the Treatise, the philosophical belief that objects cause and resemble perceptions is due largely to the effects of the imagination. While reason may play an auxiliary role, Hume's point is that the philosophical belief is not the product of reason alone.

In the Enquiry, Hume raises similar concerns about the inability of reasoning by itself to establish the Double Existence Conclusion. He observes that there are any number of putative causes of our perceptions besides objects: our own minds, other minds, or something else unknown (EHU 12.11; SBN 153). He continues:

It is a question of fact, whether the perceptions of the senses be produced by external objects, resembling them: How shall this question be determined? By experience surely; as all other questions of a like nature. But here experience is, and must be entirely silent. The mind has never any thing present to it but the perceptions, and cannot possibly reach any experience of their connexion with objects. The supposition of such a connexion is, therefore, without any foundation in reasoning.

(EHU 12.12; SBN 153)

Neither the supposed causal relation nor resemblance can be established directly by reasoning, because we are never directly acquainted with objects. This is essentially the same criticism that we saw in the Treatise (T 1.4.2.47; SBN 212). In the Enquiry, Hume alters the presentation somewhat, simultaneously criticizing the beliefs in causation and resemblance. But, as we saw in the Treatise, Hume raises the same objection to each: objects are in principle unobservable, so there is no direct way to establish either relation.

So the basis for the Double Existence Conclusion is either the senses or the imagination. Objects are in principle unobservable, so there is no way to sense them: "the senses are only the inlets, through which these images are conveyed, without being able to produce any immediate intercourse between the mind and the object" (EHU 12.9; SBN 152). So the senses cannot be the "foundation" for belief in the Double Existence Conclusion either (EHU 12.12; SBN 153). Therefore, the belief must arise fundamentally from the imagination. To put it in terms that I have been employing in this paper, the premises that are drawn upon in DTA to reach the Double Existence Conclusion must be premises contributed by the imagination. But Hume does not mention the imagination in the passages from Section 12 of the Enquiry. Instead, the imaginative propensities are described as the instinctive "faith in [the] senses."

It might be thought that equating the Enquiry's instinctive "faith in [the] senses" with unreflective acceptance of the Treatise's imaginative propensities is too great an interpretative leap. But even in the Treatise, Hume equates acceptance of the effects of the imagination with "faith in our senses." In the skeptical climax of "Of scepticism with regard to the senses," Hume writes:

I begun this subject with premising, that we ought to have an implicit faith in our senses, and that this wou'd be the conclusion, I shou'd draw from the whole of my reasoning. But to be ingenuous, I feel myself at present of a quite contrary sentiment, and am more inclin'd to repose no faith at all in my senses, or rather imagination, than to place in it such an implicit confidence.

(T 1.4.2.56; SBN 217)

Setting aside the evaluation that Hume makes in this passage, we can see that, as scientist of human nature, he corrects the misleading claim that our beliefs about external objects require "faith in our senses"; rather as he has argued at length, beliefs about external objects arise fundamentally from imaginative invention. So "faith in our senses" really is acceptance of the effects of the imagination.

The Skeptical Opposition of Reason and Instinct

So far I have argued that if the diminishing table passage alone is interpreted as an entire argument, it does not succeed at establishing the Double Existence Conclusion. That is, reasoning about the phenomenon of perceptual relativity by itself does not prove the Double Existence Conclusion. Upon examining Hume's discussion of the effects of natural instinct, I argued that we can distinguish two different stages. The second stage is contradicted by the Dependence Conclusion. The first stage is fundamentally operative in the Double Existence Conclusion, contributing the belief that something external exists and that the external existent causes and resembles our perceptions. On my interpretation, in the Enquiry, Hume is not committed to believing that the Double Existence Conclusion is completely a logical consequence of reasoning about perceptual relativity. Instead, just as in the Treatise, instinct plays a fundamental role in the invention of the philosophical system.

A proper interpretation of DTA requires recognizing its situation in the context of a skeptical argument. In this section, I carefully examine the Enquiry's skeptical argument that opposes reason and instinct and purports to show that neither by itself offers a philosophically satisfactory belief in external existence. I argue that the skeptical dilemma presupposes that instinct and reason are mutually exclusive. On this assumption, when philosophers appeal to reasoning about perceptual relativity, they reject instinct and embrace reason. But double existence is not a logical implication of perceptual relativity and therefore is not justifiable by reason alone. So philosophers who see reason and instinct as mutually exclusive are unable to escape the skeptic's dilemma. However, a scientist of human nature, who reflects on the philosophical rejection of instinct, comes to see that there are distinctions to be drawn. First, the Dependence Conclusion is to be distinguished from the Double Existence Conclusion, and second, the different effects of instinct are to be distinguished. Philosophers reject only some of instinct's effects and (perhaps unwittingly) incorporate others into their own philosophical system. Thus the skeptical argument allows a scientist of human nature to discover the fundamental role that instinct plays in the philosophical belief in double existence.

Let's begin with Hume's summary of the skeptic's argument. He writes:

Thus the first philosophical objection to the evidence of sense or to the opinion of external existence consists in this, that such an opinion, if rested on natural instinct, is contrary to reason, and if referred to reason, is contrary to natural instinct, and at the same time carries no rational evidence with it, to convince an impartial enquirer.

(EHU 12.16; SBN 155)

If one relies solely upon instinct, one adopts the vulgar belief. After reflection on perceptual relativity, philosophers find that the vulgar belief is contrary to reason. So instinct alone produces a false belief. In light of this conclusion, philosophers correct the false belief, introducing the distinction between perceptions and objects. This new belief is "contrary to natural instinct," insofar as it is contrary to the vulgar belief. Is the philosophical belief satisfactory to reason? No, the skeptic says, because no argument (causal or demonstrative) can be offered that, relying upon reason alone, entails the double existence of objects and perceptions. So when the choices are either instinct alone or reason alone, no satisfactory belief is available.

In order for this skeptical argument to get started—that is, in order for reason to oppose instinct—reason has to succeed at displacing the instinctive vulgar belief.³⁹ At a minimum, the skeptical argument is committed to the soundness of inferring the Dependence Conclusion from perceptual relativity. I contend that the skeptical objection requires us to regard philosophers as thinking that the Double Existence Conclusion is similarly inferred by reason. To support this, consider how Hume continues immediately following the diminishing table passage:

So far, then, are we necessitated by reasoning to contradict or depart from the primary instincts of nature, and to embrace a new system with regard to the evidence of our senses. But here philosophy finds herself extremely embarrassed, when she would justify this new system, and obviate the cavils and objections of the sceptics. She can no longer plead the infallible and irresistible instinct of nature: For that led us to a quite different system, which is acknowledged fallible and even erroneous. And to justify this pretended philosophical system, by a chain of clear and convincing argument, or even any appearance of argument, exceeds the power of all human capacity.

(EHU 12.10; SBN 152)

Reasoning about perceptual relativity "necessitate[s]" two effects. First, philosophers reject the belief generated by the "primary instincts of nature." This is the Dependence Conclusion, which contradicts the vulgar belief. Secondly, philosophers "embrace a new system with regard to the evidence of our senses." This is the Double Existence Conclusion, which introduces the new category of objects and affirms that perceptions are caused by and resemble objects. The "embarrass[ment]" to philosophy concerns the justification of the philosophical system. Thus the central problem concerns the Double Existence Conclusion, not the Dependence Conclusion.

This may be confirmed by looking at the three paragraphs that develop the skeptical assault on the justification of the philosophical system. In the first, Hume asks, "By what argument can it be proved, that the perceptions of the mind must be caused by external objects, entirely different from them, though resembling them (if that be possible) …?" (EHU 12.11; SBN 152–3). Alternative causes include one's own mind, the mind of some other being, or something else unknown. Perceptions do sometimes arise from one's mind, as in the case of dreams or hallucinations.⁴⁰ To decide this "question of fact," we have to consult experience (EHU 12.12; SBN 153). (Substantive causal claims are matters of fact; because these alternative causes are conceivable and therefore possible (and even actual in the case of dreams), the claim that our perceptions are caused by objects is not a relation of ideas.) But the double existence theory holds that objects are in principle unobservable, so we cannot experience the conjunction of objects and ideas or compare them. Hume observes, "The supposition of such a connexion is, therefore, without any foundation in reasoning" (EHU 12.12; SBN 153). Hume adds that the Cartesian move of appealing to a divine guarantee of the reliability of our senses does not help: "if the external world be once called in question, we shall be at a loss to find arguments, by which we may prove the existence of that Being or any of his attributes" (EHU 12.13; SBN 153). All of this shows that it is the Double Existence Conclusion that lacks "rational evidence" (EHU 12.16; SBN 155).

Hume summarizes the skeptical conclusion:

Do you follow the instincts and propensities of nature, may they say, in assenting to the veracity of sense? But these lead you to believe, that the very perception or sensible image is the external object. Do you disclaim this principle, in order to embrace a more rational opinion, that the perceptions are only representations of something external? You here depart from your natural propensities and more obvious sentiments; and yet are not able to satisfy your reason, which can never find any convincing argument from experience to prove, that the perceptions are connected with any external objects.

(EHU 12.14; SBN 153–4)

Again, the skeptical argument requires us to see instinct and reason as wholly opposed. When people follow instinct entirely, they adopt the vulgar belief. This is the opinion, "rested on natural instinct" (EHU 12.16; SBN 155). Philosophers who reflect on perceptual relativity acknowledge that the vulgar belief is "fallible and even erroneous" (EHU 12.10; SBN 152), and therefore they "disclaim" instinct entirely. So the skeptic turns to the other horn. The philosophical belief is described as "more rational" because it consults reason. In particular, the philosophical belief incorporates the Dependence Conclusion (which is arrived at through reasoning) into its belief. The Dependence Conclusion is directly opposed to the effect of the second stage of instinct (and therefore "contrary to natural instinct" (EHU 12.16; SBN 155)), and in this respect, philosophers "depart from" their natural propensities. However, there is no "convincing argument from experience to prove" that objects cause or resemble perceptions; this conclusion cannot be reached by reason alone. Thus, the philosophical system "carries no rational evidence with it, to convince an impartial enquirer" (EHU 12.16; SBN 155). An "impartial enquirer" will be one who submits the philosophical opinion to the examination of reason alone; such an enquirer will not be persuaded. If one were to suspend all human instincts (per impossibile), one would never arrive at the philosophical system. Thus on the supposition that reason and instinct are mutually exclusive, philosophers are unable to adopt any belief in external existence. Philosophers are thereby forced into skepticism.

Later in the third part of Enquiry 12, Hume criticizes such excessive skepticism. Instead, he proposes a kind of "mitigated" skepticism, "which may be the natural result of the Pyrrhonian doubts and scruples." This skepticism involves "the limitation of our enquiries to such subjects as are best adapted to the narrow capacity of human understanding." Hume writes:

A correct Judgment observes a contrary method, and avoiding all distant and high enquiries, confines itself to common life, and to such subjects as fall under daily practice and experience; leaving the more sublime topics to the embellishment of poets and orators, or to the arts of priests and politicians. To bring us to so salutary a determination, nothing can be more serviceable, than to be once thoroughly convinced of the force of the Pyrrhonian doubt, and of the impossibility, that any thing, but the strong power of natural instinct, could free us from it. Those who have a propensity to philosophy, will still continue their researches; because they reflect, that, besides the immediate pleasure, attending such an occupation, philosophical decisions are nothing but the reflections of common life, methodized and corrected. But they will never be tempted to go beyond common life, so long as they consider the imperfection of those faculties which they employ, their narrow reach, and their inaccurate operations.

(EHU 12.25; SBN 162)

It may be thought that Hume hereby excludes any inquiry concerning the belief in external existence from the bounds of philosophical consideration. On my interpretation this is not right. Instead, the philosopher finds his Pyrrhonian doubts overturned by the strength of natural instinct. Rather than cease philosophizing altogether, he returns to examine the skeptical argument and the effects of instinct more closely. This philosopher, who works through the Pyrrhonian opposition of reason and instinct, comes to discover his own deep and abiding instinctive commitments to repose faith in his senses and believe that something external exists—commitments that are more fundamental than the vulgar belief. The philosopher becomes a scientist of human nature and discovers the fundamental role of instinct in any belief in external existence.

More precisely, the scientist of human nature can make two distinctions, one regarding reason and one regarding instinct. First, the philosophical system involves two conclusions, the Dependence Conclusion and the Double Existence Conclusion. The Dependence Conclusion, which is reached by reasoning about perceptual relativity, is "contrary to" the vulgar belief. Philosophers also endorse the Double Existence Conclusion, but this is not proven from reasoning about perceptual relativity. No argument that draws upon reason alone can establish the Double Existence Conclusion. Because philosophers accept both conclusions, they find themselves simultaneously embracing reason (the opinion that is "referred to reason") and holding a view with "no rational evidence" (EHU 12.16; SBN 155).

Secondly, as I have argued throughout this paper, we can distinguish the effects of natural instinct: reposing faith in our senses, believing that something external exists, and believing that the very thing we sense is the external object. We see that the Dependence Conclusion contradicts only the last of these effects, the vulgar belief. So philosophers are unable to endorse the vulgar belief. This need not amount to a wholesale rejection of instinct. Further, once he distinguishes the effects of instinct, the scientist of human nature discovers that instinct plays a fundamental role in the philosophical double existence theory. The scientist of human nature thus comes to realize the unavoidability of natural instinct in beliefs about external existence.

Thus it is in two different senses that reason "necessitate[s]" that philosophers adopt the double existence of objects and perceptions (EHU 12.10; SBN 152). The Dependence Conclusion is a logical consequence of reasoning about perceptual relativity. The Dependence Conclusion contradicts the vulgar belief. But the first stage of instinct requires that philosophers qua human animals believe that something exists externally. So philosophers, upon rejecting the vulgar belief, are moved to distinguish objects from perceptions. Thus reason necessitates the Dependence Conclusion as a logical consequence; but the Double Existence Conclusion is not entirely a logical consequence of reasoning about perceptual relativity. Instead, reason cooperates with instinct in the philosophical invention.

The Non-Argument Interpretation

The puzzle with which this paper began was that DTA, particularly the Double Existence Conclusion, seems to be at odds with the Treatise's DVA and subsequent discussion of how philosophers come to adopt the double existence theory. In the development of the skeptical tension between reason and instinct, Hume argues that no argument can be offered for the Double Existence Conclusion. So the diminishing table passage cannot be interpreted as an argument that on its own establishes the Double Existence Conclusion. Thus the Enquiry is not at odds with the Treatise. In my interpretative reconstruction, I have shown that the Enquiry retains the insight (developed more fully in the Treatise) that natural instinct is fundamentally operative in the development of the philosophical double existence hypothesis.

One might claim that there is no tension (apparent or real) between the Treatise and the Enquiry, because no argument is offered in the diminishing table passage. Instead, Hume merely describes the received view of his philosophical predecessors.⁴¹ Michael G.F. Martin considers this interpretation:

Although we have the appearance here of argument, an indicated premiss concerning a case of illusion, and a conclusion drawn as such, in fact we lack the argument proper itself. No additional reasons are offered to support the conclusions drawn, apart from the supposition that how the table looks is not how it is.⁴²

Martin does not pursue this interpretation in depth, but it is possible to develop it somewhat more fully here.

First, we have already noted that in the Enquiry, unlike in the Treatise, Hume does not provide an extended discussion of the psychological propensities that produce the vulgar belief. We should not be surprised if he similarly fails to provide an extensive discussion of how those very same psychological principles help to shape the philosophical double existence theory. Since his non-skeptical philosophical predecessors typically adopted the double existence theory, he states its tenets as the "obvious dictates of reason" without further explanation.⁴³

Furthermore, it is reasonable to assume that the intended contemporary audience of Hume's Enquiry would be familiar with the philosophical positions of Descartes, Locke, among others. So it plausibly could be seen as unnecessary to rehearse their arguments for their respective double existence theories. On this interpretation, the "non-argument" involving the table is merely an illustration of the consequences of the philosophical hypothesis: what is perceived directly and immediately is a perception and varies with bodily changes, whereas what exists externally is the object, whose changes occur independently of bodily changes.⁴⁴

I do not find this interpretation attractive. Within the diminishing table passage itself, there appears to be an argument:

The table, which we see, seems to diminish, as we remove farther from it: But the real table, which exists independent of us, suffers no alteration: It was, therefore, nothing but its image, which was present to the mind.

(EHU 12.9; SBN 152)

It is natural to interpret "therefore" as signalling logical implication. On both the Rationally Realist and Reductio Interpretations, these apparent premises establish the Dependence Conclusion. In that respect it seems appropriate to treat the passage as presenting an argument—at a minimum, an argument for the Dependence Conclusion.

While I cannot argue conclusively against the "non-argument" interpretation, nevertheless I think any interpretation has to adopt my distinctions to understand Hume's discussion of the first "more profound" skeptical argument against the evidence of sense. First, one has to distinguish the effects of the first and second stages of instinct. Let's suppose, for the sake of argument, that there is no distinction to be drawn regarding instinct; instinct is simple and undifferentiated and always yields the vulgar belief. Philosophers who reason about perceptual relativity show the falsity of the vulgar belief and reject instinct entirely. By their own conclusion, philosophers would be unable to draw upon anything other than reason to establish their philosophical system; yet reason is insufficient to do so. As we have seen, philosophers (unwittingly) draw upon instinct. But if we did not distinguish the different stages of instinct, the instinct that philosophers (unwittingly) draw upon would be one and the same instinct that produces the vulgar belief. Philosophers thus would be engaged in a flat contradiction.⁴⁵ But the flatly contradictory system is not what philosophical endorse; philosophers do not say that what I directly and immediately perceive both has and does not have external existence. Rather they distinguish what I directly and immediately perceive from something else. The belief that there is something else that has external existence cannot be understood as being produced by an instinct that always leads to the vulgar belief, but must be understood as being produced by an instinct that, if unrestricted, will produce the vulgar belief. Thus there are different stages and effects of instinct.

Secondly, I think one has to recognize the distinction between the Dependence Conclusion and the Double Existence Conclusion. First, Hume states them in two different clauses: "So far, then, are we necessitated by reasoning to contradict or depart from the primary instincts of nature, and to embrace a new system with regard to the evidence of our senses" (EHU 12.10; SBN 152). Secondly, these two conclusions are contrasted in the skeptical argument. One is taken to be established successfully by reasoning about perceptual relativity. If reason did not succeed in this much, the skeptical argument would not be able to oppose reason to instinct. The other conclusion is taken to be insufficiently supported by reason alone—it lacks "rational evidence."

If one makes these distinctions, however, why not interpret the diminishing table passage as an argument? The premises needed to draw the Dependence Conclusion are stated in the diminishing table passage, and the effects of instinct required to combine with reason to produce the Double Existence Conclusion are stated earlier in the first paragraph concerning the effects of instinct.

Criticism of My Interpretative Strategy

Throughout this paper, I have insisted that Hume treats the development of the philosophical belief in a parallel manner in the Treatise and Enquiry. Recall that I initially criticized the Rationally Realist Interpretation for departing from Hume's comments about the scope of conclusions from perceptual relativity in the Treatise, by holding that DTA logically entails the double existence of perceptions and objects. (The supplemental premises from natural instinct mitigate this criticism.) It may be objected that my interpretative strategy assumes too much—perhaps Hume changes his mind in the later work.

It is possible that Hume presents different arguments in the Treatise and the Enquiry. Nevertheless, as I have argued, the skeptical objection requires that reason successfully displaces the vulgar belief and that reason alone fails to establish the double existence theory. These points were made more straightforwardly in the Treatise as observations about the logical consequences of DVA. Furthermore, as I have argued, the philosophical belief does not simultaneously reject and accept the content of the vulgar belief; rather it rejects the vulgar belief and accepts the vulgar faith in our senses, including the vulgar conviction that something has external existence. So if we pursue interpreting the diminishing table passage as an argument, it must be supplemented with additional premises. The first stage of natural instinct is all that is available. And its effects are sufficient to connect the Dependence Conclusion to the Double Existence Conclusion. Hume makes clear that the first stage of instinct supplies us with the belief that something external exists. Since the Dependence Conclusion shows the falsity of the vulgar belief, philosophers invent objects. And we saw that "faith in [our] senses" can produce the belief in causation and resemblance between objects and perceptions. Thus upon closer examination of natural instinct's contribution, the parallel between the accounts of the development of the philosophical belief from the vulgar belief in the Enquiry and the Treatise becomes undeniable.

Concluding Remarks

In the beginning of this paper, I argued that the vulgar beliefs that Hume describes in the Treatise and the Enquiry are fundamentally the same with regard to content, strength, and objective situation. In the Treatise, Hume claims that DVA (or any other similar argument from perceptual relativity) shows only that the vulgar belief that I perceive a stone, for example, is false. (That is, the argument shows that what we directly and immediately perceive does not have distinct existence and therefore does not have external existence.) The argument does not support the philosophical belief in the external existence of objects that cause and resemble our perceptions. Instead, such a belief depends fundamentally on the persistent effects of imaginative propensities. In the Enquiry, after describing the vulgar belief, Hume presents the conclusions of the "slightest philosophy." In it, he describes another case of perceptual relativity, from which it is concluded that the vulgar belief is false and that objects cause and resemble perceptions. I have argued that Hume has not changed his mind in the later work; DTA, like DVA, shows the falsity of one and the same vulgar belief. Moreover, on my interpretation, in the Enquiry Hume still holds that no reasoning about the raw data of sense alone can lead us to the Double Existence Conclusion; such a belief depends upon the influence of lasting effects of instinct.

Furthermore, I have argued that the effects of instinct that Hume briefly describes in the Enquiry capture the effects of the fundamental imaginative propensities that Hume describes more fully in the Treatise. My account makes sense of why Hume separates the description of the effects of instinct into two paragraphs in the Enquiry. My account also reveals Hume to be a scientist of human nature who reflects on the Pyrrhonian argument and comes to discover the unavoidable contribution of instinct to any belief, vulgar or philosophical, in external existence.

One might wonder whether Hume should be interpreted as endorsing a double existence theory.⁴⁶ I have not argued one way or the other here. However, what I have said bears on the matter in the following way. If one wishes to interpret Hume as endorsing the double existence theory, one cannot simply point to the diminishing table passage.⁴⁷ While that passage states the Double Existence Conclusion, it does not support the conclusion by itself. In order to reach the Double Existence Conclusion, the argument has to be supplemented with premises drawn from natural instinct. It lies outside the scope of this paper to evaluate the prospects of the double existence theory any further, but complications will immediately arise concerning the second "more profound" skeptical objection to the philosophical primary-secondary quality distinction (EHU 12.15; SBN 154–5).