The Humors in Hume's Skepticism

1. An Overlooked Question

In the striking concluding section (1.4.7) of the first book of A Treatise of Human Nature, David Hume pauses his project of “explain[ing] the principles of human nature” (T Intro.6, SBN xvi)¹ to survey his findings so far. Doing so fills him with “desponding reflections” about “the wretched condition, weakness, and disorder” of human cognitive faculties. Since Hume must use these faculties in his project, “melancholy” and “despair” replace his normal vigor for it, and “discourage [him] from further enquiries” (T 1.4.7.1–3, SBN 264–65).

By the end of the short section, however, Hume finds himself again in an “easy disposition” of “good humour.” He feels ready to “contribute a little to the advancement of knowledge”—to bring his science of man “a little more into fashion.” He invites his readers to “follow [him] in [his] further speculations” in the Treatise’s latter books (T 1.4.7.14, SBN 273).

Interpreters have placed great weight on this curious transformation. Understanding how Hume emerges from melancholy to again embrace philosophy has seemed to be the key to Hume’s considered views in the Treatise on the roles of skepticism and philosophy in human life.² And so it has seemed crucial to understand the transformation’s structure and details.

Any complete account of the transformation must note that it is far from immediate. Hume does not pass directly from his skeptical melancholy to resumed interest in philosophy. Rather, his transformation involves several distinct stages: After plunging into melancholy (1.4.7.1–8), Hume stops engaging in philosophy to enjoy social pleasures (1.4.7.9); then feels aggression toward philosophy (1.4.7.10); then composes his mind through restful activities (1.4.7.12); and finally finds himself curious and ready to resume his philosophy (1.4.7.12 and 14). The succession can be pictured as follows:

Hume’s stages in 1.4.7

melancholy

→

sociability

→

aggression

→

composure

→

curiosity

Why does Hume pass through these several stages, in this order, and no others? Interpreters often miss the question, despite their interest in Hume’s transformation. Or rather, many are content to attribute Hume’s passage through these stages to ‘nature’ without further explanation. Barry Stroud, for example, stresses “the naturalness and virtual inevitability of reflecting philsophically” (2011: 155). Hume does report at the end of the process that he is “naturally inclin’d” to reflect and “cannot forbear having a curiosity” about philosophical topics (T 1.4.7.12, SBN 270–71). But noting the naturalness of the process does not itself shed light on the significance or order of the stages that compose it. It does not explain why Hume’s specific progression, as opposed to any other, is the natural one.

Annette Baier distinguishes several “swings in moods” along the way, noting that the “transitions” Hume undergoes “are motivated … merely by the incompleteness of the initial mood, its natural fate of supplementation by a successor mood” (1991: 20–21). But she does not specify in what sense the moods are incomplete or bound to lead to some specific successor. Similarly, Don Garrett views Hume’s transformation as involving several shifts of what he calls “moods” or, after Hume, “bents of mind” (see Garrett 2002: esp. 231–37). But he does not explain why the aggressive mood is, as he puts it, a “natural successor to philosophical melancholy and delirium” (Garrett 2008: 165). Nor does he explain how it is a natural precursor to renewed interest in philosophy.

Some interpreters emphasize the role of two passions in Hume’s return to philosophy. When it comes to Hume’s decision “whether he should recommit himself to philosophy,” Henry Allison writes: “Fortunately for both Hume and us this decision is made for him by the re-emergence of the inclination to philosophize, fostered by the passions of curiosity and ambition” (2008: 324). On Karl Schafer’s view, “the real foundation of Hume’s rejection of radical skepticism and of his positive epistemology more generally” is “a distinctively Humean account of epistemic virtue” based in the satisfaction of passions like curiosity (2014: 4). According to Donald Ainslie, Hume’s “return to philosophy is driven primarily by his feelings” (2015: 225).³ But none of these interpreters offers an account of why these passions arise so prominently when they do. We seem forced again to point to nature, without understanding its operations.

I think we can say more. First, we can expose and clarify an interpretive question that has not received due attention. This is the question of why Hume undergoes the exact succession of stages he does—why he moves from melancholy to sociability, to aggression, to composure, and finally to curiosity. Second, we can answer the question. We can explain the significance, order, and completeness of the stages. In doing so, we uncover a striking and unappreciated view of skepticism and its role in human life.

One important clue is the distinctive language Hume uses when describing the succession of stages. There, he speaks of “melancholy” (T 1.4.7.1, SBN 264; 1.4.7.9, SBN 269) and “spleen” (T 1.4.7.11, SBN 270; see, also, “splenetic” at 1.4.7.10, SBN 269), and makes frequent allusions to the other “humours” (T 1.4.7.10, SBN 269; 1.4.7.11, SBN 270; 1.4.7.14, SBN 273) of ancient and medieval medicine. In what follows, I argue that Hume’s repeated invocation of the four humors is the key to understanding why he portrays himself as moving through the stages he does. For Hume views his recovery from melancholy as, or as mediated by, a series of shifts in the temperaments of humoral theory. I call this ‘the humoral reading’ of 1.4.7, and develop it in §2 below.⁴

I then consider two natural objections to the reading. §3 addresses what I call ‘the anachronism objection.’ This is the charge that it is anachronistic to claim that Hume drew inspiration from an ancient theory of medicine. In response, I argue that humoral theory not only appears throughout Hume’s own writings and early sources, but also retained a modest influence over early eighteenth-century Scottish medicine. §4 addresses what I call ‘the methodology objection.’ This is the charge that the humoral reading portrays Hume as violating an apparent methodological commitment to avoid appealing to the bodily causes of mental phenomena. In response, I explain that Hume makes frequent appeals to human physiology. But I suggest that his appeals are meant to offer models for thinking about the mind, without thereby committing him to any one theory of the parts or functions of the body. If that is right, Hume’s invocations of the humors throughout 1.4.7 suggest that he models his progression on the four temperaments of humoral psychology, without his needing to endorse the associated physiology.

In §5, I turn to the humoral reading’s most important philosophical upshots. The reading, I argue, sheds a new light on the nature and significance of skepticism. On that reading, 1.4.7 offers a picture of health or proper functioning as a balance of basic temperaments of mind. The humoral reading, together with other aspects of Hume’s discussions of skepticism, suggests that, for Hume, skepticism is primarily a temperament—a temperament which, when balanced with others, produces the proper doxastic disposition. This conception, I argue, helps to resolve an important puzzle about Hume’s view of skepticism. The puzzle concerns how Hume can consider skepticism to be both an illness and a cure. Conceiving of skepticism as a temperament resolves the puzzle, because a temperament can be an illness when overly predominant, and a cure when moderate. This resolution in turn presents additional evidence that Hume held such a conception.

Though this conception of skepticism is shaped by humoral theory, it can interest us even if the theory is false. We do not need to conceive of health as consisting in a proper proportion of humors in order to appreciate Hume’s idea that skepticism is a temperament which, according to its degree of predominance, can both threaten and restore the mind’s proper functioning. This is a unique and illuminating conception of the nature, source, and proper treatment of skepticism. On that conception, skepticism is not a theory as much as a temperament; its familiar and threatening manifestations do not arise from argument as much as from temperamental excess; and their proper resolution comes less through counterargument than through counterbalance by other temperaments.

2. A Cycle through the Humors

According to humoral theory, health requires a balance or proper proportion of four basic bodily liquids, called ‘humors.’ Disease, both mental and physical, occurs when one of these humors is overabundant or deficient, either throughout the body or in one of its parts.⁵

The theory’s four humors, canonized in the Hippocratic text Nature of Man, are blood, yellow bile (or choler), black bile (or melancholy), and phlegm.⁶ Hippocrates associated each humor with a season and stage of life in which it was thought to be abundant.⁷ Over the centuries, the humors took on further associations. Galen of Pergamon, for example, emphasized that each humor, like each season, was either hot or cold and either wet or dry, and was thus associated with one of the four elements of nature: air, fire, water, and earth.⁸ Later, each humor became associated with one of four temperaments—roughly, clusters of psychological and physiological traits and dispositions. Each temperament involved a tendency to feel characteristic passions, engage in certain actions, and develop physical features and ailments associated with related body archetypes. Though individuals, and whole nations, were often thought to be born with prevailing temperaments, a person’s temperament could sometimes change with shifts in life-stage, environment, or season. It was thought that the more of a given humor one had, the more its corresponding temperament was expressed, and vice versa.⁹

Humoral therapies aimed at restoring humoral balance by dissolving or curbing the production of excessive humors, or promoting the production or retention of deficient ones. This was accomplished first and foremost by the adoption of regimens for the so-called “six non-naturals”: food, evacuation of wastes, exercise, air, sleep, and passions. Activities like study, music, and various social pleasures were prescribed for the effects they had on one’s passionate, and so humoral, constitution. If the ailment was severe, more invasive treatment, like purgative herbs or blood-letting, was used to expel excessive humors. But this harsher treatment was generally reserved for cases in which diet and regimen would not suffice.¹⁰

Figure 1:

The four humors sorted as hot or cold, and wet or dry, with associated season, life stage, element of nature, and temperament. Descriptors of the temperaments are listed in italics

The rich set of humoral associations provided a framework for disease prognosis, diagnosis, treatment, and prevention. Because blood was thought to predominate in the spring and in youth, for example, special precautions would be taken in those times to avoid and treat ailments of excessive blood, like hemorrhaging. Sanguine youths, for example, were made to avoid meats and other ‘blood-rich’ foods, vigorous exercise in the heat, and excessive mirth.¹¹

One disease, perhaps more than any other, garnered perennial interest among writers in the humoral tradition. This was melancholy: a lingering agitation, depression, or madness, without fever, that was usually attended with baseless fear and sadness.¹² According to humoral theory, melancholy was the extreme expression of a dominating humor—in this case, black bile. Indeed, the word ‘melancholy’ comes from the Greek for black (melas) and bile (kholos). Cold, dry black bile was associated with reflection, pensiveness, idleness, and caution in moderate quantities, and depression, doubt, paralysis, and madness in excessive quantities. Black bile encouraged arduous, focused thought—the kind employed in mathematics, philosophy, and other sober or scholarly pursuits.¹³ And those pursuits encouraged more black bile, either directly¹⁴ or because they tended to inspire melancholic sentiments when they, through their content or difficulty, revealed our own cognitive limitations.¹⁵

Humoral allusions pervade Hume’s discussion of melancholy. Hume calls his melancholy a “deplorable condition” (T 1.4.7.8, SBN 269), and depicts it in a way that fits the classic humoral description of the ailment: a sustained depression with bouts of madness attended by unprompted fear and sadness. He describes his melancholy as a “delirium” (T 1.4.7.9, SBN 269) and himself as “affrighted” and “forlorn” (T 1.4.7.2, SBN 264). When Hume describes his survey of his philosophy’s skeptical strands as “heat[ing his] brain” (T 1.4.7.8, SBN 268), he alludes to one of the primary ways accumulated black bile was thought to cause melancholic delirium: Black bile in the abdomen or blood produces hot vapors which rise to the brain, heat it, and obscure thought.¹⁶ Accordingly, Hume describes himself as tormented with “clouds” (T 1.4.7.9, SBN 269) and a “storm” (T 1.4.7.2, SBN 264). Melancholics were thought to retreat to dark, solitary places and imagine themselves to have transformed into fearful beasts.¹⁷ In the throes of melancholy, Hume reports: “I fancy myself some strange uncouth monster, who not being able to mingle and unite in society, has been expell’d from all human commerce, and left utterly abandon’d and disconsolate …. inviron’d with the deepest darkness” (T 1.4.7.2, SBN 264; 1.4.7.8, SBN 269). This leaves Hume craving, among other things, the “warmth of the crowd” (T 1.4.7.2, SBN 264) to counterbalance black bile’s frigidity and tendency toward isolation.

Hume does in fact break free from his melancholy by joining the crowd. He dines, plays backgammon, and makes merry with friends (T 1.4.7.9, SBN 269). In enjoying social pleasures, he partakes in the most common humoral remedies for melancholy. According to humoral theory, melancholy tends to nurture itself by encouraging strained and obsessive thoughts. Social pleasures combat this vicious cycle, by distracting us from these thoughts and promoting blood.¹⁸ Hume emphasizes these two points. He tells us that a “person of a sorrowful and melancholy disposition is very credulous of every thing, that nourishes his prevailing passion” (T 1.3.10.4, SBN 120).¹⁹ And, in the Treatise’s second book, he explains that our natural aversion to melancholy urges us to seek out the excitements of social life:

Those, who take a pleasure in declaiming against human nature, have observ’d, that man is altogether insufficient to support himself; and that when you loosen all the holds, which he has of external objects, he immediately drops down into the deepest melancholy and despair. From this, say they, proceeds that continual search after amusement in gaming, in hunting, in business; by which we endeavour to forget ourselves, and excite our spirits from the languid state, into which they fall, when not sustain’d by some brisk and lively emotion. To this method of thinking I so far agree, that I own the mind to be insufficient, of itself, to its own entertainment, and that it naturally seeks after foreign objects, which may produce a lively sensation, and agitate the spirits. On the appearance of such an object it awakes, as it were, from a dream: The blood flows with a new tide: The heart is elevated: And the whole man acquires a vigour, which he cannot command in his solitary and calm moments. (T 2.2.4.4, SBN 352–53)

Here, Hume agrees with the misanthropes that our distaste for melancholy drives a “continual,” and so inevitable, “search for amusement.” Such amusements, he agrees, “produce a lively sensation,” dispelling the melancholy. Notably, Hume adds a further, physiological explanation: The amusement dispels the melancholy by causing a “new tide” of blood. While this remark can naturally evoke the mechanistic physiologies that emerged in the late seventeenth century,²⁰ it is equally at home in a humoral framework. In the latter, the connection to psychology is more direct. Warm, wet blood was thought to be the most abundant humor, and for that reason the most balanced and typically conducive to health. Accordingly, the sanguine temperament, brought about by a predominance of blood, was social, carefree, active, and optimistic, though sometimes headstrong. Hume’s use of the word ‘sanguine’ would seem to agree. For he speaks of “sanguine tempers” that are “social” and “sincere” but “impetuous” (H 3.24.31; 3.27.11; 3.27.20), as well as the “sanguine hopes of young adventurers” (H 5.41.43; see, also, H 3.25.27; EHU 1.12, SBN 12). It is thus plausible that he would see an increase in blood or circulation as helping to present philosophy in an attractive light—as an enterprise in which one may make real accomplishments. That could foster adventurous passions like curiosity and ambition.

Hume’s merriments over dinner and backgammon play a pivotal role in his recovery. The infusion of warm blood they provide raises him from the darkest depths. It cuts short his obsessive, despondent reflections and invigorates him, breaking his paralysis. But Hume’s recovery is not yet complete. Philosophical speculations do not yet interest him, but rather appear “so cold” in contrast to the invigoration of social life that Hume “cannot find it in [his] heart to enter into them any farther” (T 1.4.7.9, SBN 269). The contrast is perspicuous because the blood infusion does not fully vanquish Hume’s melancholy, leaving significant “remains of [that] former disposition” (T 1.4.7.10, SBN 269). The extent of this melancholic residue may reflect the severity of Hume’s initial humoral imbalance. While melancholic, he “fanc[ies himself] in the most deplorable condition possible, inviron’d with the deepest darkness, and utterly depriv’d of the use of every member and faculty” (T 1.4.7.8, SBN 269). Correcting that degree of excess calls for drastic medicine. When regimen does not suffice, a purge may be needed to restore balance.

Hume does not mention purgative medicines. But the next stage of his recovery is characterized by a desire for a purge of sorts. For Hume, the poison which must be expelled is philosophy. He reports, “I am ready to throw all my books and papers into the fire” (T 1.4.7.10, SBN 269). Of the four humors, yellow bile, or choler, was seen as most suited for purgation. Its heat and dryness were thought to encourage diarrhea and vomiting—hence, the name of the disease cholera. Likewise, many melancholy-purging drugs had hot and dry natures.²¹ This allowed them to dissolve and evacuate black bile which persisted through treatment by regimen. It is fitting, then, that Hume wishes to destroy his books with hot, dry fire—the element associated with yellow bile.

Hume describes himself in this stage as “governed” by a “splenetic humour” (T 1.4.7.10, SBN 269). One of the senses of the word ‘splenetic’ is ‘melancholic.’ So it is tempting to think Hume is returning to black bile here—after all, black bile is thought to reside in the spleen, and some melancholic diseases to result from spleen dysfunction.²² But ‘splenetic’ has another, quite different meaning of ‘given or liable to fits of angry impatience or irritability; ill-humored, testy, irascible.’ The Oxford English Dictionary lists this sense as particularly common throughout the eighteenth century, when Hume wrote.²³ And it seems to be the sense Hume has in mind, since the splenetic humor makes him impulsive and aggressive. These dispositions are more characteristic of the bilious or choleric temperament than the melancholic.²⁴ And the presence of fire imagery further suggests that it is a surge of yellow bile which clears Hume of melancholic residue.

Still, no curiosity or ambition emerges at this stage. For the yellow bile fosters a felt aggression toward philosophy, which now seems an enemy—“against the current of nature,” even “torture” (T 1.4.7.10, SBN 269–70). Hume’s curiosity and ambition return only after he has “tir’d with amusment and company, and [has] indulg’d a revery in [his] chamber, or a solitary walk by a riverside.” Only then does he report: “I feel my mind all collected within itself, and am naturally inclin’d to carry my mind” to philosophical topics (T 1.4.7.12, SBN 270). These quiet, calming activities and resulting composure are plausibly associated with the fourth and final humor: phlegm.²⁵ People with phlegmatic temperaments are generally peaceful, inactive, and equanimous, when not just slothful or indolent. And Hume’s “riverside” walk gives a subtle nod to phlegm’s association with water.²⁶

Hume’s phlegmatic activities are a fitting rejoinder to his previous splenetic humor, given that cool, wet phlegm is most opposed to hot, dry yellow bile. But they would have offered no therapy, and so would not have promoted balance, while Hume was under the influence of excessive black bile. At that stage, black bile would have filled those quiet and solitary moments with obsessive and despondent thoughts. But the same activities can be therapeutic now that blood has dissolved, and yellow bile expunged, the excessive black bile. With the added phlegm they provide, Hume can “collect” his mind. And once it is collected, he can emerge from the phlegm to engage in more focused thought.

Having made a full cycle through all four humors, Hume finds himself in humoral balance. Health is restored, and with it the inclination to indulge in some reflection. Only now does Hume feel the “curiosity to be acquainted with the principles of moral good and evil, the nature and foundation of government, and the cause of those several passions and inclinations, which actuate and govern [him]” (T 1.4.7.12, SBN 270–71). As if to drive home the requirement of balanced humors for curiosity, Hume invites readers “of the same easy disposition” as him to join him in further speculation, while advising those who are not to “wait the returns of application and good humour” (T 1.4.7.14, SBN 273).

We can summarize the humoral reading of the transformation as follows:

Hume’s stages in 1.4.7, with corresponding humors

melancholy	→	sociability	→	aggression	→	composure	→	curiosity
black bile	→	blood	→	yellow bile	→	phlegm	→	health

Earlier, I asked why Hume undergoes the particular succession of stages in 1.4.7. The humoral reading answers this interpretive question. It explains why there are five stages, in the order they appear, with the characteristic sentiments and activities they have. The melancholic humor and temperament urges an eventual invigoration of the blood through social activity; this leaves significant melancholic remains, which must be purged through the aggression of yellow bile; the restoration of phlegm must come last among the individual humors, because so long as significant melancholic excess remains, phlegmatic activities will fill Hume with desponding thoughts and plunge him back into melancholy; and health comes after that because it requires a balance of all the humors. If the humoral vocabulary and imagery throughout 1.4.7 offered nothing more than a dramatic tone, then the interpretive question would remain unaddressed. But in fact Hume’s language can clue us in to the framework in which he conceives of his recovery—a framework which explains the succession of its stages.

We can still ask: To what extent is this progression particular to Hume? Is Hume’s description of it meant to be more than a self-report? Is it more? If Hume’s imbalance is especially severe, his cure too might be somewhat unusual. It might not always be necessary, for example, to cycle through all four humors in order to reach a balance. Perhaps sometimes a new tide of blood from “some avocation” may suffice as medicine. Hume may perhaps even allow that a melancholic “bent of mind” could, in some cases, “relax” on its own (T 1.4.7.9, SBN 269).²⁷ Humoral theory does not always require the precise sequence of 1.4.7 to restore balance. Instead, the rich and systematic humoral language of 1.4.7 show vividly that Hume conceives of recovery in humoral terms.

3. The Anachronism Objection

The humoral reading portrays Hume as drawing systematically from an ancient theory of medicine. But Hume is in many ways a modern thinker. He wrote in a time of “enlightenment,” often characterized in terms of its replacement of classical scientific theories with remarkable innovations. Reading Hume as appealing to an antiquated, and to us occult, theory of medicine can then seem anachronistic and fantastic. I call this the anachronism objection. If the objection is correct, we might then read Hume’s uses of ‘melancholy’ to be like ours, referring to a sentiment divorced from any associated humor or temperament.²⁸ Indeed, we might wonder whether Hume was familiar with humoral theory at all.

A first step toward answering this objection is to show that Hume was indeed familiar with humoral theory. If the abundant humoral language of 1.4.7 does not convince us, there is strong evidence elsewhere in Hume’s corpus. In Dialogues Concerning Natural Religion, for example, Hume’s character Philo expresses a humoral conception of health: “On the mixture and secretion of the humours and juices of the body depend the health and prosperity of the animal,” as humors “frequently become pernicious, by [their] excess or defect” (DNR 11.11, KS 209–10). Soon after, Philo speaks of the “600 different muscles” and “284 bones” of Galenic anatomy (DNR 12.3, KS 215), suggesting the author’s knowledge of Galenic doctrines. In the Enquiry Concerning Human Understanding, Hume describes a painful case of gout as caused by “malignant humours in [the] body” (EHU 8.34, SBN 101). In the History of England, Hume describes no less than three historical figures as dying from melancholy.²⁹ And in the Treatise, he seems to endorse the theory when he says, for example, that “the mixture of humours and the composition of minute parts may justly be presum’d to be somewhat different in men from what it is in mere animals” (T 2.1.12.2, SBN 325). In these passages, Hume suggests that our bodies are composed of humors and that humoral imbalance causes disorders. These are the fundamentals of humoral theory.

Hume’s familiarity with humoral theory is also suggested by its presence in the philosophical and critical texts Hume read while preparing the Treatise. Cicero’s Tusculan Disputations, for instance, draws an analogy between the “disorder” of a mind plagued by false education and “distempers and sickness … bred in the body from the corruption of blood, and the too great abundance of phlegm and bile” (Cicero 1877: Bk. IV, Ch. X, p. 136).³⁰ More notable yet are the vivid references to the theory of temperaments in Abbé J. B. Dubos’s 1719 Critical reflections on poetry, painting and music, which Hume no doubt read in preparation for his planned portion of the Treatise on “Criticism.”³¹ These appear, for example, in Dubos’s explanations of how painters “bring us acquainted with … the temperament” of their subjects, using physiognomy, hair color, and posture (1719/1748: 78). He writes of Charles-Antoine Coypel’s Susanna Accused of Adultery:

The painter has diversified the complexions of the famous old men [crowded around the accused]; one appears fresh and sanguine, and the other choleric and melancholy. The latter, pursuant to the proper character of his temperament, which is obstinacy, commits the crime with heat and resolution. Rage and fury spread through his whole countenance. The sanguine old fellow seems to relent, and, notwithstanding all the transport of his passion, feels a remorse that staggers his resolution. This is the natural character of men of that kind of complexion. (Dubos 1719/1748: 82–83) ³²

In this passage and others, Dubos invokes groupings of imagistic, physiognomic, and psychological tropes that have their root in Galenic writings—the choleric’s face betrays the “heat” of his rage and fury. Such passages surely contributed to Hume’s fluency with the psychology and imagery associated with the four temperaments.³³

But even had Hume never read Dubos, these associations would still have been familiar from the literary canon. To deny this would be to claim that Hume never encountered or appreciated Shakespeare’s “life … made of four” (Sonnet XLV), or Milton’s “melancholy damp of a cold and dry” (Paradise Lost, Pt. II, Bk. XI, lines 542–545), or any of Ben Jonson’s numerous “comedies of humours,”³⁴ not to mention the frequent humoral allusions throughout Molière’s plays.³⁵ Educated eighteenth century readers—Hume included—were well acquainted with the use of humoral tropes to capture certain well-worn character types and to explore pivotal facets of human nature—for example, our caprice, tendency towards extremity, incompleteness in romantic longing, or mortality.³⁶ In such a context, there was nothing bizarre about Hume’s drawing inspiration from humoral theory, whose imagery he rightly expected his readers to recognize.

If Hume had detailed knowledge of humoral theory, it is not unnatural to take the abundant humoral language of 1.4.7 at face value. Hume would have understood what he was so repeatedly alluding to. Nevertheless, those familiar with Hume’s scientific context may still doubt that Hume meant these allusions as more than dramatic flourishes. Despite its enduring presence in European culture and thought, humoral theory was in decline, and, at the academies of the young Hume’s Scotland, had largely been replaced by more modern medical theories. There, like much of the early eighteenth century British Isles, a mechanistic physiology prevailed.³⁷ Contemporary Scottish mechanists like George Cheyne viewed “the Human Body” as a “Machin of infinite Number and Variety of different Channels and Pipes, filled with various and different Liquors and Fluids” (1733: 4).

By itself, an understanding of Hume’s medical context can simply lead us to think that Hume himself was out of touch with current medicine. But, as interpreters have noted,³⁸ mechanistic views can also be found in Hume’s own writings. Throughout the Treatise’s “anatomy of the mind” (T 2.1.12.2, SBN 326; cf. 1.4.6.23, SBN 263; 3.3.6.6, SBN 620–21; A 2, SBN 646), Hume’s pervasive talk of the transfer of force and vivacity from impression to idea seems to draw on the notions of particle motion and fluid dynamics so central to mechanistic physiology. Describing this sort of transfer in the case of poetical associations, Hume says that the “vividness … is convey’d, as by so many pipes or canals” (T 1.3.10.7, SBN 122; cf. DP 6.19, Bea 29)—an image reminiscent of Cheyne’s body of “Channels and Pipes.” Moreover, Hume’s brief but repeating appeals to the ‘animal spirits’ in belief, association, and error reflect the brand of Cartesian mechanism which Hume encountered in the works of Malebranche and Mandeville. He seems to accept the thesis that the twists and turns of thought correlate with the motions of spirits, subtle fluids coursing through interconnected traces in the brain tissue.³⁹ These passages, and others, demonstrate the great influence of mechanistic physiology on his thought.

Perhaps more to the point in a discussion of Treatise 1.4.7, Hume had available non-humoral accounts of the nature and causes of melancholy. He shows his familiarity with one of these in a 1734 letter addressed to an anonymous physician, possibly Cheyne.⁴⁰ In the letter, Hume complains of a depressive “Distemper” with “repeated Interruptions” of his “Train of Thought,” initially diagnosed as “the Disease of the Learned” (HL 3.14–16). As interpreters have noted, this particular label for melancholic or “hypochondrical” disorders likely derives from Mandeville’s 1715 A Treatise of Hypochondriack and Hysterick Passions.⁴¹ That text favorably repeats mechanistic views, while mocking Galenism.⁴² According to Mandeville, melancholy occurs when “the labour of the Brain [has] exhausted … the finest Spirits” (1715: 149). Hume seems to employ this mechanistic account in his letter. He compares and contrasts his “present Condition” with a “Want of Spirits,” describes philosophical studies as “wasting” his spirits, and asks whether his “Spirits [will ever] regain their former Spring and Vigor” (HL 3.13, 14, 18). This strongly suggests that Hume had a mechanistic account of melancholy available, and indeed one that was more in line with his scientific context. Why insist that it is Hume who is out of touch, and not the humoral reading?

I think neither is out of touch. Despite the rise of newer physiologies, humoral theory continued to influence the medicine of Hume’s time. As medical historians have noted, humoral theory’s decline was “slow, one of evolution rather than revolution,” and still incomplete (Porter 1987: 47). ⁴³ Amidst all the innovation, Galenism remained surprisingly entrenched in Scottish medical practice. Early eighteenth century Scottish physicians and surgeons continued to diagnose and treat symptoms according to a humoral scheme, prescribing traditional remedies like blood-letting and purges. Their familiarity with humoral theory was reinforced by the medical education available. Before the founding of Edinburgh’s medical school in 1726, aspiring Scottish physicians traveled to mainland Europe, studying at the more affordable universities of Padua, Reims, and, especially, Leiden. Many of the university courses they attended consisted primarily in descriptive lectures on classical texts, including broadly humoral treatises from antiquity. At Leiden, for example, MD candidates were required to expound several Hippocratic aphorisms as a part of their examinations.⁴⁴ As a result, most Scottish physicians practicing during Hume’s youth stocked their libraries with the medical classics, especially Hippocratic texts (Dingwall 1995: 145).

Even the mechanistic medical texts of Hume’s contemporaries sometimes preserved or revived key elements of humoral theory. Cheyne is a good example. His 1724 Essay of Health and Long Life focuses on the management of the classic six “non-naturals”: “1. The Air we breath in. 2. Our Meat and Drink. 3. Our Sleep and Watching. 4. Our Exercise and Rest. 5. Our Evacuation and their Obstructions. 6. The Passions of our Minds” (1724: 2). This six-part division of the regimen structures the entire text. And Cheyne concludes with a call for balance strongly reminiscent of the Hippocratic doctrine of health as proper proportion, urging his readers to “observe the golden Mean in all their Passions, Appetites and Desires” (1724: 120). Similarly, Cheyne’s treatise on melancholy, The English Malady, revived the Hippocratic notion of a national temperament, shaped by atmospheric conditions and cultural mores, and involving a proneness to certain diseases—in England’s case, a variety of “nervous Distempers” (1733: i–ii).⁴⁵ Even if Cheyne’s mechanism abandoned the schema of four humors, his medicine still preserved important elements from the humoral tradition. These include the idea of health as a kind of balance; the idea that health is best maintained and restored through the management of the six non-naturals; and the idea that atmospheric and geographical conditions shaped national characters and diseases.

Ultimately, the humoral reading, as I defined it, does not require commitment to the underlying physiology of the four humors. It attributes to Hume the view that health requires a balance of the temperaments of humoral theory. This conception of health was by no means long gone in Hume’s day, and it is not antiquarian to suggest that he took it seriously. Though certainly in decline, humoral medicine still had some currency in Hume’s Scotland. In this respect, the anachronism objection is itself anachronistic. Still, the objection raises an important question that has so far not been answered. Did Hume in fact believe in the underlying physiology of the four bodily humors? The evidence of his mechanism can leave a lingering doubt about the extent to which he accepted humoral theory. To answer this question, I turn next to Hume’s views about the role of physiology in his philosophical method.

4. The Methodology Objection

The humoral reading can seem fundamentally at odds with Hume’s experimental method in the Treatise. For Hume seems to express a methodological commitment to avoid appealing to any specific theory of human physiology. When leaving aside certain passions in the Treatise’s second book, Hume says: “the examination of them wou’d lead me too far from my present subject, into the sciences of anatomy and natural philosophy” (T 2.1.1.2, SBN 275–76).⁴⁶ The same commitment seems to underlie Hume’s introduction of “impressions of sensation” as “aris[ing] in the soul originally, from unknown causes” (T 1.1.2.1, SBN 7, my italics). By choosing not to specify the causes of such impressions, Hume can seem to relegate the laws by which they enter the mind to natural philosophy, excluding them from philosophy proper. His doing so can seem to suggest that he thinks such laws would fail to give properly philosophical explanations of mental phenomena.⁴⁷ And that would seem to suggest that Hume would bar physiological theories from doing explanatory work in his philosophy. If that is right, and Hume stays faithful to this methodological commitment, then he cannot appeal to humoral theory to explain the succession of impressions and ideas in 1.4.7. I call this the methodology objection.

One possible reply is to deny that Hume is fully faithful to this methodological commitment, if he holds it at all. For Hume seems to give numerous, straightforwardly physiological explanations of mental phenomena. He says, for example, that an “extraordinary ferment of the blood and spirits” is a cause of madness, and a “new tide” of blood interrupts melancholy (T 1.3.10.9, SBN 123; 2.2.4.4, SBN 352–53). In at least one passage, Hume explicitly announces that he “must … have recourse” to physiology to explain the mental phenomenon at issue. There, he is trying to “account for the mistakes that arise from [the] relations” of resemblance, contiguity, and causation. In other words, Hume wants to explain why, when thinking about some object, we unawarely replace it with another object that only resembles the first, or that we previously experienced nearby or in close succession with the first. To do so, he conducts “an imaginary dissection of the brain”:

I shall … observe, that as the mind is endow’d with a power of exciting any idea it pleases; whenever it dispatches the spirits into that region of the brain, in which the idea is plac’d; these spirits always excite the idea, when they run precisely into the proper traces, and rummage that cell, which belongs to the idea. But as their motion is seldom direct, and naturally turns a little to the one side or the other; for this reason the animal spirits, falling into the contiguous traces, present other related ideas in lieu of that which the mind desir’d at first to survey. This change we are not always sensible of; but continuing still the same train of thought, make use of the related idea, which is presented to us, and employ it in our reasoning, as if it were the same with what we demanded. This is the cause of many mistakes and sophisms in philosophy; as will naturally be imagin’d, and as it wou’d be easy to shew, if there was occasion. (T 1.2.5.20, SBN 60–61)

On the psychophysiological theory of mind Hume invokes, each idea is “plac’d” in a region of the brain. When the mind is about to “excite” a certain idea, it “dispatches” the spirits, sending them along traces in the brain tissue toward a “cell” which houses that idea. If the spirits reach the cell, we form the idea. But since the flow of the spirits is naturally a bit erratic, the spirits divert into nearby traces, and so arrive at different cells and lead us to form different ideas. So far, this falls short of a complete explanation of why the ideas we end up with bear relations of resemblance, contiguity, or causation to the first idea—the one toward whose cell the spirits were first “dispatched.” For that, we would need a further story about why ideas which bear these relations are located on contiguous brain traces. Hume does not give this story. He instead seems to presuppose his readers’ familiarity with it—that his talk of ‘spirits,’ ‘cells,’ and ‘traces’ would be sufficient to prompt his readers to fill in the relevant details.⁴⁸ We need not concern ourselves with the details here.

The passage is of interest insofar as it seems to be a stark example of Hume reaching for a physiological explanation. It is true that Hume apologizes for the explanation he gives here, noting that it is in conflict with the “first maxim” of his philosophy. But that maxim does not say or imply that he must avoid physiological explanation. It instead says “that we must rest contented with experience” as the test of our judgments. Hume’s “dissection” violates that maxim because the physiology he appeals to is “an imaginary dissection of the brain,” rather than one drawn from experience (T 1.2.5.20, SBN 60, my emphasis). In short, he apologizes not for his explanation’s being physiological, but for its being speculative.

This passage, and others, suggest that Hume does invoke physiological explanations after all. Their prevalence may lead us to question whether it is really a feature of Hume’s methodology to avoid appeals to physiology. Doubting that Hume holds such a commitment could perhaps motivate a reading of the seemingly methodological passages as merely delineating the topic of Hume’s inquiries. On that reading, Hume does not restrict what sorts of things can figure in his explanations, but rather what sorts of things he is to explain in the first place. He relieves himself of the obligation to give explanations that would take him deep into the details of human physiology. And he is prudent to do so, since such explanations would require “experiments” of a very different sort than his “cautious observation of human life … in the common course of the world, by men’s behaviour in company, in affairs, and in their pleasures” (T Intro.10, SBN xix). But this need not bar physiological explanations from appearing in Hume’s theory of the mind altogether. Perhaps some topics, like that of the sentiments and ideas which appear in a mind recovering from melancholy, may benefit from drawing on a rich tradition of physiological explanation.

I think this reply to the methodology objection holds water. But Hume’s “imaginary dissection” also provides a second and at least as compelling reply. For his discussion of the “dissection” suggests a general lesson about why Hume bothers to state the physiological causes of some of his topics of interest. Just before conducting the “dissection,” Hume says something very curious:

I shall only premise, that we must distinguish exactly betwixt the phænomenon itself [making mistakes across the three relations], and the causes, which I shall assign for it [the diversion of animal spirits across contiguous brain traces]; and must not imagine from any uncertainty in the latter, that the former is also uncertain. The phænomenon may be real, tho’ my explication be chimerical. The falshood of the one is no consequence of that of the other. (T 1.2.5.20, SBN 60)

Here, Hume tells us that his own physiological explanation for the relevant mistakes in reasoning might be “chimerical.” His caution here would be in keeping with his Scottish Newtonian predecessors, who took animal spirits to be an antiquated fiction.⁴⁹ Nonetheless, Hume reassures his reader that the “falshood” of the causal explanation he is about to offer would not imply the falsehood of the “principle” he is trying to explain. But this raises the question: What could be the point of invoking an admittedly dubious physiological cause? What does Hume hope to gain by doing that?

The answer, I think, is that citing a physiological cause invokes a larger physiological story or framework, which serves as a rich source of analogy for thinking about the mind. Such an answer is suggested by remarks earlier in the Treatise. Here, Hume discusses the importance of analogy to the “explication” of a certain mental phenomenon at issue—in this case, how our particular ideas can become general in their representation. He says: “To explain the ultimate causes of our mental actions is impossible. ‘Tis sufficient, if we can give any satisfactory account of them from experience and analogy” (T 1.1.7.11, SBN 22). Hume’s imaginary dissection does not provide us with an account from experience, since it is imaginary. But Hume’s story about diverted spirits, and the story about the formation of brain traces which Hume expects his readers to fill in, together with the general framework of fluid dynamics which both stories share, provide rich analogies for understanding the kind of error at issue. In this case, spatial and mechanical notions offer a way to think about how the mind makes its unnoticed substitutions of ideas across the three relations. Whether or not the stories have really got our physiology right is not crucial for Hume’s enterprise. One or more of the stories might turn out to be false, or impossible to judge, but no matter. The analogies they offer would still, in that case, give anyone familiar with the stories and frameworks a way of thinking about the mind—a way which could illustrate the “principle” at issue, and bring about a kind of satisfaction.

If that is right, Hume need not commit himself to the correctness of the exact physiological stories he gives. In the case of mechanistic explanation, his imaginary dissection does not require a belief in the existence of animal spirits. This may reveal a limited sense in which the methodological objection is on point: From time to time, Hume evinces wariness about committing himself to the literal truth of this or that physiological theory, even while he is willing to state its theses. As a result, it is often unclear from the text whether Hume endorses the physiological theses he states, even half-heartedly. But his level of endorsement does not always matter for his purposes. Even someone who rejects those theses could make room for the analogical use of physiological theses and frameworks, especially if she expected her audience to have prior familiarity with them.

We can now see that the humoral reading need not attribute endorsement of humoral physiology to Hume. In the end, I think it is genuinely unclear whether, or to what extent, Hume believed in humoral physiology. But it does not matter. For the humoral reading can interpret Hume’s talk of bodily humors as meant to offer analogies for understanding the workings of the mind. Presumably, such analogies would suggest that the mind, like humoral theory’s picture of the body, has four basic elements which, when balanced, constitute health or proper functioning. But that is precisely the core of humoral theory’s psychological part. The primary resource Hume borrows from humoral theory, then, is its robust temperament psychology.

When first expounding the humoral reading in §2, I described the progression of stages in 1.4.7 in largely physiological terms: an excess of black bile, dissolved by a “new tide” of blood, expunged by yellow bile, cooled by phlegm. Doing so helped to make perspicuous the various oppositions between the stages, and thus the logic behind their succession. But we can now take this language to be analogical, and so read Hume’s progression as modeled only on humoral psychology: melancholy, invigorated by sanguinity, scorned by biliousness, calmed by phlegm. We can then summarize the humoral reading finally in terms of a succession of temperaments:

Hume’s stages in 1.4.7, with corresponding temperaments

melancholy	→	sociability	→	aggression	→	composure	→	curiosity
melancholic	→	sanguine	→	bilious	→	phlegmatic	→	even-tempered

This would be a humoral reading which jettisons the underlying physiology of gross bodily fluids—a reading on which healthy mental functioning consists in the balance of four basic psychological temperaments, bearing the same relations of opposition as their physiological counterparts, each having tendencies to cause or be caused by characteristic sentiments and activities. That would still be a ripe source of explanation.

In summary, the methodology objection objects that Hume would bar physiological theories, such as that of humoral medicine, from doing explanatory work in his philosophy. The first reply I considered was that Hume includes a range of physiological explanations throughout the Treatise. The second reply was that Hume’s apparent invocations of humoral physiology can be read as analogies, rather than as literal endorsements, drawing on the precedent set by Hume’s remarks on the use of analogies in explaining the mind. One reply denies Hume’s exclusion of physiology; the other accommodates it. In either case, Hume’s invocation of the humors is consistent with his actual method. Either reply is enough to answer the methodology objection. And I am inclined to think both are correct. Hume makes apparently physiological claims throughout the Treatise, and 1.4.7 is no exception. And these claims are a rich source of analogy, whether or not Hume literally believes them. Either way, the stages of 1.4.7 can be seen as a cycle through the four temperaments en route to psychic balance.

5. Reconceiving Hume’s Skepticism

The four humors or temperaments, together with their characteristic activities and sentiments, explain Hume’s succession of stages in 1.4.7. They also provide insight into his views on skepticism. Hume’s association of skepticism with the melancholic humor or temperament encourages us to rethink both what he thinks skepticism is, and what role he takes it to play in human life.

First, the association suggests that skepticism itself can be understood as a temperament, or disposition to think, act, and feel in certain ways, which can be more or less dominant, and expressed to greater and lesser degrees. The melancholic temperament, which tends to inspire engagement in inquiry, caution in forming beliefs, and a felt doubt or unease concerning one’s limitations, is a natural candidate for the tendency of mind Hume labels “scepticism.” When such a temperament dominates, unchecked by the other temperaments, one loses one’s grip on reality and sinks into a gloomy “delirium.” But when the temperament is balanced with others, it can contribute the carefulness, focus, and awareness of one’s abilities needed for sober and scientific pursuits.⁵⁰

The humoral reading alone does not force us to see Hume as viewing skepticism as a temperament. It only suggests this interpretation. But the suggestion is supported by the language Hume uses when discussing skepticism. In the Treatise, he speaks of a “sceptical disposition” (T 1.4.7.10, SBN 269), and often uses the word ‘disposition’ in close proximity and interchangeably with ‘temper.’⁵¹ Hume acknowledges that this disposition or temper admits of varying degrees of intensity. In the Appendix to the Treatise, for example, he speaks of “a modest scepticism to a certain degree” (T 1.2.5.26n12, SBN 639). And in Treatise 1.4.3, he speaks of the “true philosopher” as embodying a “moderate scepticism” (T 1.4.3.10, SBN 224). These modest and moderate degrees contrast with an extreme skepticism, which Hume labels “total” (T 1.4.1.7, SBN 183; 1.4.7.7, SBN 268) and “extravagant” (T 1.4.2.50, SBN 214; 1.4.4.6, SBN 227–28; cf. EHU 12.17, SBN 155). We can read both of the latter labels as modifiers that express the intensity or extent of the skeptical temperament: ‘Total,’ on this reading, connotes reaching a maximum, total dominance; ‘extravagant’ connotes going too far, a lack of moderation, indulgence. Now, such a reading allows that “total skepticism” can at times refer to the scope of a doubt—to skepticism about all of our beliefs. But this is not the only way in which Hume conceives of skepticism as being or becoming “total.” In the section “Of scepticism with regard to reason” (1.4.1), he writes of an extreme loss of confidence:

When I reflect on the natural fallibility of my judgment, I have less confidence in my opinions, than when I only consider the objects concerning which I reason; and when I proceed still farther, to turn the scrutiny against every successive estimation I make of my faculties, all the rules of logic require a continual diminution, and at last a total extinction of belief and evidence. (T 1.4.1.6, SBN 183)

The melancholic temperament involves a disposition to reason, often repetitively or obsessively, and often with regard to one’s own weakness or fallibility. One who, like Hume in this passage, does not just reflect on her fallibility once, but “proceeds still farther, to turn this scrutiny against every successive estimation” could be seen, at that moment, as exhibiting an extremely skeptical temperament—indeed, a temperament that has become so ‘total’ that it now entirely characterizes her mental landscape, eclipsing all opposing dispositions to judge and feel, and so destroying her confidence in her beliefs. We may read the ‘total scepticism’ of 1.4.1, then, as the complete domination by a skeptical temperament. As Cleanthes puts it in Hume’s Dialogues Concerning Natural Religion, “total scepticism” arises “in a flush of humour” (DNR 1.6, KS 132–3).

The language of varying degrees is a point of continuity with Hume’s discussions of skepticism in the first Enquiry.⁵² In Section XII, he discusses four varieties of skepticism, grouped into two pairs. Strikingly, within each pair one variety is excessive, and a threat to reasoning and inquiry, while the other is moderate and useful.

Hume’s main concern in this section is the two varieties of skepticism which are “consequent to science and enquiry.” These are adopted only after discovering the “absolute fallaciousness” or “unfitness” of our mental faculties for their common and speculative uses (EHU 12.5, SBN 150). One of these varieties Hume calls “excessive scepticism,” and associates with the Pyrrhonian skeptics of ancient times (EHU 12.23, SBN 159; 12.24, SBN 161; cf. 12.21, SBN 158–59). The label ‘excessive’ suggests that the skepticism has been taken too far or become too dominant. It is characterized by an attempt to preserve a widespread doubt and sense of “universal perplexity and confusion” (EHU 12.24, SBN 162). The other variety Hume calls “mitigated scepticism” (EHU 12.24–25, SBN 161), and associates with the academic skeptics. ‘Mitigated’ suggests a lessening of intensity through interaction with other forces—hence, it suggests a kind of balance. And, indeed, Hume says that mitigated skepticism just is the excessive skepticism “in some measure, corrected” by other tendencies of the mind. The result is a kind of “modesty and reserve” (EHU 12.24, SBN 161).⁵³

The other two varieties of skepticism Hume discusses are “antecedent to all study and philosophy” and are meant to serve as “preservative[s] against error and precipitate judgment” (EHU 12.3, SBN 149). The first of these, which Hume associates with “Des Cartes,”

recommends an universal doubt, not only of all our former opinions and principles, but also of our very faculties; of whose veracity, say they, we must assure ourselves, by a chain of reasoning, deduced from some original principle, which cannot possibly be fallacious or deceitful. (EHU 12.3, SBN 149–50)

According to Hume, such a skepticism would be a poor preparation for philosophy, for it would leave us in perpetual suspension of judgment. By continually declining to assent to any judgement until we have assured ourselves of the veracity of our faculties, we effectively deprive ourselves of assenting to any “principle” which could provide that assurance. As a result, “no reasoning could ever bring us to a state of assurance and conviction upon any subject” (EHU 12.3, SBN 150). In the next paragraph, however, Hume acknowledges that the very same “species” of skepticism,

when more moderate, may be understood in a very reasonable sense, and is a necessary preparative to the study of philosophy, by preserving a proper impartiality in our judgments, and weaning our mind from all those prejudices, which we may have imbibed from education or rash opinion. (EHU 12.4, SBN 150, my emphasis)

This “more moderate” variety still advises us “[t]o begin with clear and self-evident principles.” But it does not demand that we show, through a chain of reasoning, that such principles can never deceive. For a skeptic of this moderate sort, it is enough to embody a degree of caution—“to advance by timorous and sure steps, to review frequently our conclusions, and examine accurately all their consequences” (EHU 12.4, SBN 150). In adopting antecedent skepticism, then, one develops a propensity to step back and withhold any assent which is too quick and easy. This may involve checking the steps of one’s reasoning, examining before judging, making sure one has not made a mistake or imported a bias, and, when possible, looking for firmer foundations. But the “Cartesian” variety takes this to excess. One who goes so far can never find a foundation firm enough and so ends up in a continual search.

None of this is to deny that Hume sometimes uses the term ‘scepticism’ to refer to a particular, historical, philosophical sect or tradition or its core principles. Hume clearly uses the term this way at points. In the first Enquiry, for example, Hume seems to regard skepticism as a body of “philosophical principles” (EHU 12.2, SBN 149; see also 12.21, SBN 158–59; 12.23, SBN 160) that can be supported by argument or reasoning: He says that skeptics give “profound arguments against the senses” (EHU 12.6, SBN 151) and “philosophical objection[s] to the evidence of sense” (EHU 12.16, SBN 155), and that they “attempt … to destroy reason by argument and ratiocination” (EHU 12.17, SBN 155). In the Treatise, he speaks of “sceptics” as a “fantastic sect” that offers up “cavils” for their “opinions” about the “uncertainty” of our judgments (T 1.4.1.7–8, SBN 183). At first, a conception of skepticism as a temperament seems ill fit to accommodate these uses. A temperament is not a “philosophical principle,” or body thereof, or a tradition or method. And though a temperament could perhaps be adopted or inculcated as the result of reasoning, it cannot itself be the conclusion of an argument.

But a temperament can be the source of the reasoning or tendency which leads one to adopt a body of principles. Hume tells us as much when he claims that the “decisions” and “pursuits” of “almost every” philosopher are dictated by his “predominant inclination, to which his other desires and affections submit, and which governs him, though, perhaps, with some intervals, through the whole course of his life” (E Sc 1–2, Mil 159–60).⁵⁴ In this way, a temperament can stand behind, shape, and lend character or content to a body of principles. The “sceptical … system of philosophy” referred to in the title of the fourth part of the Treatise’s first book can then be read as a collection of arguments or principles that a person of a strongly inquisitive temperament would be apt to make. Such a collection could include within it a long philosophical tradition insofar as the tradition resulted from the same predominating temperament—one of continual questioning, repeated applications of reason, and the doubt which follows on their coattails. And Hume can call his philosophical exploration of the human understanding “sceptical” insofar as its repeated application of causal reasoning “tends to give us a notion of the imperfections and narrow limits of human understanding” (A 27, SBN 657).

The idea that a philosophical sect or system can be characterized by a predominating temperament can seem foreign. But in viewing the skeptical system in this light, Hume in effect takes a more classical perspective on the character of philosophical traditions. That perspective views them primarily in terms of competing ways of living, and secondarily in terms of the arguments or principles which could be used to justify those lived dispositions. In that light, the ‘skeptikos’ is first and foremost just what that word means: a person who ‘scopes out,’ observes, considers, examines, or inquires.⁵⁵ Though the historical sects may have, as a matter of fact, been characterized by an excess in these activities, a more moderate kind is possible.

As we have seen, Hume characterizes skepticism both as a temperament and as a doctrine, rather than only as a temperament. But the temperamental conception appears to be primary. Hume uses the skeptical temperament to explain the appearance of skeptical doctrines. And a preponderance of temperamental language reveals a widespread emphasis on the temperamental conception. This conception finds textual support in Hume’s repeated invocation of the humors, his talk of skepticism as a disposition, his emphasis on varying degrees of skepticism and on its moderation or excess, and his association of skepticism with caution. These are not easily accommodated by a conception of skepticism as a doctrine or theory.

The conception of skepticism as a temperament also allows us to resolve a puzzle about skepticism’s role in Hume’s theory of human nature. For Hume seems to say conflicting things. He calls skepticism a “malady” (T 1.4.2.57, SBN 218), and describes its unpleasant symptoms in great detail. But he also treats it as an aid, prescribing “tinctures” of it to “abate” certain ailments (EHU 12.24, SBN 161), and saying: “[i]n all incidents of life we ought still to preserve our scepticism” (T 1.4.7.11, SBN 270). How can a single phenomenon, skepticism, be both disease and medicine? The likening of skepticism to the melancholic temperament of humoral theory offers an answer. A humor or temperament has varying degrees of intensity; it can both dominate, destroying healthy psychic balance, and be moderate, restoring or maintaining this balance. Hume can call skepticism a “malady,” because it is harmful when it is overabundant and grips the mind with too much intensity. And Hume can treat skepticism as a medicine: In appropriate doses, usually small, it can temper excesses in the other humors or temperaments, and contribute its share of the dispositions that together constitute a healthy mind.

Hume describes this function in the first Enquiry:

If any of the learned be inclined, from their natural temper, to haughtiness or obstinacy, a small tincture of Pyrrhonism might abate their pride, by shewing them, that the few advantages, which they have attained over their fellow, are but inconsiderable, if compared with the universal perplexity and confusion, which is inherent in human nature. (EHU 12.24, SBN 161)

Hume does not specify which humor or temperament characterizes the “natural temper” he has in mind.⁵⁶ But he comes closer in Treatise 1.4.7, where he describes the kind of person who can benefit from skepticism as having a “warm imagination.” Someone with a warm imagination, Hume says, dogmatically embraces philosophical “hypotheses … merely for being specious and agreeable” (T 1.4.7.14, SBN 272). If uneducated, such a person is prone to a kind of religious frenzy or raving which Hume calls ‘enthusiasm.’ For Hume, warmth of the imagination proceeds from “luxuriant health” and “a bold and confident disposition” (E SE 3, Mil 74)—all of which are characteristic of the temperament associated with excessive blood. We can thus conclude that Hume attributes obstinacy and dogmatism to excessive sanguinity. An overly sanguine temperament, he thinks, can be treated by a brief experience of skeptical philosophy. A short glimpse of the depressing state of our cognitive faculties can contribute the “degree of doubt, and caution, and modesty, which, in all kinds of scrutiny and decision, ought for ever to accompany a just reasoner” (EHU 12.24, SBN 162).

Hume can then be read as offering the skeptical strands of his own philosophy as the preferred melancholic tonic. Because such a tonic can treat other humoral or temperamental excesses—especially the unbridled enthusiasm and dogmatism of excessive blood or sanguinity—it belongs within our arsenal of cures as human beings interested in living balanced, healthy lives.

This, I imagine, is Hume’s primary intention in considering skepticism in the context of a recovery from melancholy described in humoral terms. He shows us not only how to emerge from our own intellectual depressions, but also how the experience of that depression can be an education—how it can prepare us to cure ourselves and others of other disorders or imbalances.

If the humoral reading of 1.4.7 is right, then the common interpretation that Hume rejects a kind of skeptical theory in that section is distorting in two important ways. According to that interpretation, what Hume rejects is a theory of human knowledge on which we can know very little—presumably, a theory implied or inspired by some of Hume’s findings earlier in the Treatise. In contemporary philosophy, the word ‘skepticism’ often refers to just that: a negative or austere theory of human knowledge adopted on philosophical grounds. It is “the view that we know nothing, or that nothing is certain, or that everything is open to doubt” (Stroud 1984: vii) or “that we know very little or nothing of what we think we know” (Nozick 1981: 197).⁵⁷ But importing this sense of the word into Hume’s thought can obscure the fact that he generally conceives of skepticism at least largely as a temperament. After all, a theory is not a disease, or cure, or disposition. Secondly, Hume does not exactly reject skepticism in 1.4.7, any more than he simply accepts it. Rather, he tempers it. On his view, eradicating skepticism would be unhealthy. Instead, he moderates skepticism, considered as a temperament, by counterbalancing it with our other tendencies of thought and feeling.

6. Conclusion

At this point, we might wonder: What are Hume’s views about the substantive doctrines associated with skepticism? What should we make of his arguments for or against those doctrines? The humoral reading suggests a way to approach these questions. We can use humoral theory’s conception of health to help determine whether skeptical doctrines arise from a healthy state of mind. We can then ask whether Hume draws a close connection between health and balance on the one hand, and truth and justification on the other.⁵⁸ If he does, considerations of health and balance would play a crucial role in Hume’s views about what we should believe.

I have not attempted to address these further questions here. Instead, I have offered a defense of the humoral reading, and have used it to reconceive Hume’s skepticism and resolve two important puzzles. First, the humoral reading answers our interpretive puzzle about the succession of the stages in 1.4.7. As I have argued, Hume’s pervasive humoral vocabulary and imagery reveal that he views his recovery from melancholy as a cycle through the four humors or temperaments, leading finally to their balance. Second, the humoral reading helps to explain how Hume can see skepticism as both a disease and a cure. It does so by encouraging us to see Hume as viewing skepticism as a temperament, subject to both excess and moderation.

Why is this reading novel? Why have Hume’s humoral allusions gone mostly unnoticed? The answer, I suspect, is this: Because humoral theory has long since fallen from favor, contemporary readers are apt to view the allusions as mere artful flourishes, rather than the terms of art they are. Michael Williams calls 1.4.7 “one of the most dramatic expositions of skeptical doubt ever set down” (2004: 267). Ainslie goes a step further, imagining it “must be the most literary stretch of writing in the English-language philosophical canon” (2015: 218).⁵⁹ While this praise may be deserved, I think it has sometimes obscured the extent to which Hume’s choice of words and images in 1.4.7 serves not only his aesthetic ends, but also his philosophical ones. What can look like lyricism or eighteenth century “charm” is in fact a substantive doctrine.

That doctrine is a conception of health as a balance of temperaments, each of which contributes its share of dispositions to reason and believe in certain ways. The melancholic, or skeptical, temperament contributes doubt, caution, and modesty to our reasoning and inquiry. The sanguine temperament contributes hope and confidence. The bilious and phlegmatic, though they receive less discussion, still plausibly contribute resolve and equanimity, respectively.⁶⁰ In excess, any of these dispositions becomes pernicious: The melancholic grows into widespread doubt and madness; the sanguine into hasty dogmatism and zealotry; the bilious into short-sightedness; and the phlegmatic into dullness. But, when cooperating through mutual checks and balances, they produce a “just reasoner” (EHU 12.24, SBN 162). Sanguine confidence gets inquiry off the ground, while melancholic caution keeps it from soaring too high. Even the “indolence” of the phlegmatic temperament, Hume thinks, contributes a safeguard against tarrying too long in abstruse reflection (EHU 1.12, SBN 12).

The core of this conception is separable not only from humoral physiology, but also from the humoral psychology of the four temperaments. Its basic idea is that proper mental functioning involves a balance of tendencies to reason and believe in certain ways, and that certain epistemic vices, such as skepticism and dogmatism, are the extreme expression of the very same tendencies. These vices are then more a matter of degree than of doctrine. As a result, even skeptics and dogmatists can lead us toward proper mental functioning, when adopting some share of their dispositions helps us correct our own imbalances. We do not need to accept humoral theory, or even its psychological portion, in order to appreciate or accept this idea. Nonetheless, it is an idea that Hume’s invocations of humoral theory can lead us to see for the first time.

So is Hume, then, offering a kind of ‘virtue epistemology’? Hume’s use of humoral theory suggests a way in which it is not misleading to say that Hume thinks of skepticism in terms of virtue: a skeptical temperament, to the right degree, contributes to excellence in reasoning and believing. But this is not the broadly pragmatic conception of virtue we find later in the Treatise, centered on the usefulness and agreeableness of a character trait. It is, instead, the more typically Aristotelian picture of proper functioning, and especially of balance, that plays the decisive role in Hume’s conception and treatment of skepticism.⁶¹ This balance is a mean with respect to various dispositions, each of which tempers the others. It is in this context that skepticism emerges for Hume as a stage, a temperament, a malady, and a cure.