Shayne Wissler
“… to understand is, above all, to unify.” – Albert Camus

Criticizing David Hume’s Enquiry Concerning Human Understanding

April 15 2017

“[A] Philosopher who affects to doubt of the Maxims of common Reason, and even of his Senses, declares sufficiently that he is not in earnest, and that he intends not to advance an Opinion which he would recommend as Standards of Judgment and Action.”

— David Hume

This article is a criticism of David Hume’s An Enquiry Concerning Human Understanding. But even more it is a criticism of the army of Hume’s misinterpreters. Since I use aspects of Hume’s analysis in my REASON and LIBERTY, I have an interest in distancing myself from these misinterpretations[1]. Having bought in to what I now consider propaganda about Hume’s ideas – namely, that his ideas are tantamount to crass skepticism (the notion that all we know is that we know nothing, and not even that) – I had not been interested in reading this work until Fall 2012. So before critiquing Hume – who I regard as one of the intellectual giants of The Enlightenment – a critique of his critics is in order.

“Man, as the minister and interpreter of nature, does and understands as much as his observations on the order of nature… permit him; and neither knows nor is capable of more.”

— Francis Bacon

Certainly, Hume’s work questions the very foundations of our inductive knowledge. A superficial reading could lead one to think that, by attacking what is actually fake knowledge, he has rejected all knowledge. This is particularly true when the reader’s own base of knowledge is without foundation – since Hume repudiated the reader’s false foundation (which the reader yet dogmatically persists in), he feels that Hume has indicted all genuine knowledge whatsoever. And so this superficial reader quite naturally reports to the world that Hume is an arch-skeptic. But is Hume really an arch-naturalist, reporting on the nature of authentic human knowledge.

A related problem is that most who report on Hume’s ideas cite him on his A Treatise of Human Nature, not the more carefully crafted and mature Enquiry. This fallacious approach to Hume stretches all the way back to Hume’s time, who in the introduction to Enquiry wrote:

“Most of the principles, and reasonings, contained in this volume, were published in a work in three volumes, called A Treatise of Human Nature: a work which the Author had projected before he left College, and which he wrote and published not long after. But not finding it successful, he was sensible of his error in going to the press too early, and he cast the whole anew in the following pieces, where some negligences in his former reasoning and more in the expression, are, he hopes, corrected. Yet several writers who have honoured the Author’s Philosophy with answers, have taken care to direct all their batteries against that juvenile work, which the author never acknowledged, and have affected to triumph in any advantages, which, they imagined, they had obtained over it: A practice very contrary to all rules of candour and fair-dealing, and a strong instance of those polemical artifices which a bigotted zeal thinks itself authorized to employ. Henceforth, the Author desires, that the following Pieces may alone be regarded as containing his philosophical sentiments and principles.”

If anyone wishes to praise or criticize Treatise, that is fine, but they shouldn’t be unqualifiedly advertising it as “Hume’s ideas”. And if any self-styled scholar does so, he should be ashamed.

Several ways superficial readers of Hume have erred are that (1) they fail to consider that Hume’s program requires incorporating his discoveries about ideas into our entire vocabulary; (2) they interpret “constant conjunction” in the narrowest possible sense, rather than in the broadest possible; (3) they confuse Hume’s occasional injection of his own skeptical attitudes and moods with his actual arguments.

Regarding (1), they might say “Hume proved (or aimed to prove) that we can’t know anything about reality.” But in fact, Hume demonstrated that one sort of knowledge is fake, and another sort is legitimate. To which type then should the term “knowledge” apply? Hume’s point wasn’t that we can’t know, it was that when we do know, that the nature of that knowledge is that it’s rooted in constant conjunction, i.e. in our natural experience, we find that this is always and without exception associated with that. When people claim that Hume proved we can’t know anything about reality, all they are doing is confessing that, to them, the term “knowledge” refers to the illegitimate type of knowledge, i.e. metaphysical nonsense not rooted in naturalistic observation.

Point (2) is more difficult and even Hume wasn’t entirely clear and explicit (however, see Section 7 below), but it should be clear that if “constant conjunction” is the right basis of knowledge then it must really be a constant conjunction. That is, we aren’t here referring to only direct experiential constant conjunction (be drop a ball and it always falls to the ground), but also indirect constant conjunction regarding the theories we develop out of our direct experience. What I mean here is that if we lay out all the propositions that correspond to absolutely every belief we hold, then no belief should contradict another, for if it does, then that means there is no constant conjunction, and therefore, no authentic knowledge. This sort of ethic is the base of science: we find that when we drop some objects they fall, but others rise, and we seek to revise our propositions such that they really do represent constant conjuction, as opposed to a pragmatic, narrow, and barbaric “it is sort of the case that a dropped object falls most of the time.”

Are we guaranteed that our knowledge is ever permanent, that we won’t ever have to rectify it again? In a natural world, who would make such a guarantee? No, legitimate knowledge is always and forever open to revision. If our knowledge is always and forever open to revision, does that mean our beliefs are any less certain, or that we have any less fervent commitment to them than one who embraces the fraudulent closed idea of knowledge? No, it just means we learn our lessons when it turns out that we’ve been wrong, including the lesson of what sort of beliefs deserve our whole commitment and what sort do not. Such is part of the meaning of wisdom. It means we, unlike dogmatists, actually improve over time.

(3) It is evident that either Hume hasn’t fully integrated the implications of his own conclusions into his own psychology, or (perhaps more likely) he likes to playfully toy with the more superficial readers by dangling skeptical attitudes that do not actually logically follow from his main arguments in front of them, or he is at times insincere as a form of self-protection (see Section 1 below). Indeed, all three may be in play at different points in the text. But these occasional skeptical remarks by Hume have no logical impact on his argument.

When reading Hume, we have to separate Hume’s unsubstantiated skeptical attitudes about what he’s argued for from what he’s actually argued very well for. For example, he argues quite correctly that ultimately our knowledge of cause and effect is founded upon experience (and not apriori reasoning), but then indicts this as “defect” and “human blindness and weakness” and so on. In former he has made a perfectly valid case, but the latter is a gross non-sequitur and mere pining and complaining (or perhaps, sarcastic mockery of the dogmatist). It does not follow that if we know in a certain way, that therefore that way is “defective.” In order to rationally call something “defective”, you first need a rational standard by which you compare, but implicitly, the only standard Hume has in mind here is the Supernatural All-Knowing God, and it is by that nonsensical standard that he’s indicted us as “defective”, which is pure silliness. So silly in fact that he likely didn’t even mean it.

Supposing that Hume really was a Dr. Jekyll and Mr. Hyde character, a mixture of a careful path-breaking genius naturalist philosopher and a painfully superficial disillusioned-mystic-turned-skeptic, how should we take him? The latter are a dime a dozen; I choose to interpret Hume as he is at his very best, because that is where the most value lies.


The following is for readers of Hume’s Enquiry, so I will generally assume here that you have the text and are reading it. His Enquiry is broken into twelve sections, but I will only here be addressing the first eight of these. The edition I am using is the 2nd edition edited by Eric Steinberg, but you can probably figure out what I’m commenting on regardless of what version of Enquiry you have.

Enquiry may very imprecisely but accurately be summed up as: “What happens when we vigorously and intensively question a philosophic axiom?”

[link]Section 1: Of the Different Species of Philosophy[link]

Hume begins with sarcastic praise for what we might call “vulgar” philosophy – i.e. philosophy which the general public finds appealing, but which is bereft of philosophical justification. I think it it is sarcastic because Hume proceeds to give an insightful and ringing defense of what he, again tongue in cheek, calls “abstruse” philosophy, by which he really means a philosophy that is attempting to be precise, accurate, and well-substantiated.

Whether we fault Hume for his lack of clarity and sincerity depends on our judgment of the historic context of his remarks. It was a fashion of this era to design controversial philosophical expression such that it would be obscure to the stupid but clear to the intelligent. The reason for this is obvious: the stupid tend to attack or kill you merely because of your opinions, and a harassed or imprisoned or dead philosopher is good to no one.

[link]Section 2: Of the Origin of Ideas[link]

Hume makes his case for the origin of ideas, namely that they are rooted in what he calls “impressions”. This is a term to which he gives a special meaning, since no word exists for the idea he has in mind.

What Hume means by “impression” is what we mean when we say “experience”, except that “impression” is intended to refer to a particular instance of experience, such as a particular taste, a visual of a particular object, the sound of someone’s voice. We could add that there are also internal impressions, such as feeling tired or nauseated; and even conscious ones, such as feeling confused or angry or having a particular remembrance. Hume makes the case that all ideas whatsoever are ultimately rooted in impressions. Even novel ideas (Hume gives the idea of a “golden mountain”) are formed from mixing ideas formed from impressions (“gold” and “mountain”).

Parallel to this case Hume makes an error. Whereas impressions and ideas are actually distinct categories, Hume ranks them in the same line, congratulating impressions for their “vivacity” and indicting ideas for their alleged relative weakness: “The most lively thought is still inferior to the dullest sensation.”

But for human beings, it is ideas that give life to impressions: a child seeing a drop of liquid on his skin may consider it less significant than a raindrop, but to a scientist who knows he’s accidentally spilled a highly toxic poison it will trigger the height of fear and impulse to action. The difference of vivacity isn’t due to the impressions, which are similar, but to the ideas, which are very different.

To create a “vivacity” vs. “dullness” contest between senses and ideas and then to declare senses the “winner” is, at least psychologically, to purvey the kind of crass skepticism of ideas that Hume himself rebukes. Nor is there any particular reason (at least that I have discerned) why it was important to his case about the origin ideas to remark on the question of “Who is more vivacious – sensations or ideas?” Again, these are different categories and there’s no legitimate philosophic need to be ranking them relative to one another.

[link]Section 3: Of the Association of Ideas[link]

Hume offers three principles of association (“connexion”) between ideas, where, he says the introduction of one idea somehow leads us to the other idea, these being Resemblance, Contiguity in time or place, and Cause and Effect. He modestly proposes that these are “complete and entire”, that there are no other principles by which ideas are associated.

Hume remarks that, as far as he knows, no other philosopher has attempted to enumerate these, however the “laws of association” began with Plato, were elaborated on by Aristotle (Contiguity, Frequency, Similarity, Contrast), as well as analyzed by John Locke[2].

Also see Aristotle’s Four Causes, “ways we can know”; and his Categories, “what in basic terms we can know”.

[link]Section 4: Sceptical Doubts concerning the Operations of the Understanding[link]

Part 1 of this section identifies experience as the foundation of (inductive) knowledge; Part 2 asks if we can somehow justify this foundation, and answers in the negative: we are at the mercy of Nature, Nature is not to be subjugated to our reasoning.

In some sense this is an obvious conclusion. (Hume: “If I be right, I pretend not to have made any mighty discovery.”) Logic is one pillar of thought, and experience is another, and neither can be justified without relying upon both. But it is instructive for Hume to draw this case out at length, to intensively question what we take as axiomatic and thus underscore its axiomatic status.

[link]Part 1[link]

Hume begins by recognizing two modes of human understanding: which he calls Relations of Ideas and Matters of Fact, but which I will call logic (how we arrive at deductive truths) and induction (how we arrive at truths via experience). In a lapse of judgment and category error analogous to his “impressions are vivacious but ideas are dim” from Section 2, he calls deduction “certain” and induction not, and also as in Section 2, none of this attitude on his part undermines his overall point and is irrelevant to his thesis.

Of the deductive he says they are “certain”, but of the inductive he says “The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality.” But induction is not deduction, these are two distinct modes of human understanding and it is a category error to rank one relative to the other. Does a person feel more certain when he deduces that the square of two sides of a triangle equals the square of the hypotenuse, or when he reflects on the fact that touching a hot stove will burn his hand? This psychological question may have more to do with whether he’s recently actually been burned or not, but in any case, it is irrelevant to Hume’s argument.

Hume writes: “I shall venture to affirm, as a general proposition, which admits of no exception, that the knowledge of this relation [of cause and effect] is not, in any instance, attained by reasonings a priori; but arises entirely from experience, when we find that objects are constantly conjoined with each other.” – Does this seem like someone who is actually “skeptical” about his inductively reached conclusions? No.

According to Hume, we can never know the “ultimate springs and principles” of nature, and therefore “the observation of human blindness and weakness is the result of all philosophy, and meets us, at every turn, in spite of our endeavors to elude or avoid it.” Let us grant Hume the former – that we will never probe to the final foundation of reality (LHC collider experiments only demonstrate some aspects of physical reality within the limits of achievable energy levels.) Still, the latter is non-sequitur and in no way follows from the former. Yes, if we’d wanted to be Gods, we are going to be disappointed. But to call the most magnificently intellectually powerful creature that (as far as we know) exists blind and weak is to overreact. We should not let our mere imagination of a Perfect Knowing Being cloud our evaluation of the very real powers we do possess.

“Nor”, he says, “is geometry, when taken into the assistance of natural philosophy, ever able to remedy this defect, or lead us into the knowledge of ultimate causes, by all that accuracy of reasoning, for which it is so justly celebrated.” Again: To indict the real limits of our inductive faculties as a “defect” is mere rhetorical flourish here; Hume’s indictment is wholly distinct from that which he indicts, and is a non-sequitur. It does not follow that because we have limits, that this is somehow a “defect.” To call something “defective” we need a standard by which to compare, and as there is no call for a rational person to use supernatural Magical Knowing Powers as the standard, we use that knowable standard that is the best that human beings have ever achieved, Issac Newton being an exemplar in his pursuits in natural philosophy.

[link]Part 2[link]

Hume recognizes inexorable tautology/circularity in any attempt to logically prove the validity of induction. However, he neglects observing that logic itself has the same quality: one can’t logically prove the validity of logic. It is unfortunate that he doesn’t explicitly note the fact that logic and experience are parallel foundations of knowledge, and that all Hume is really doing is underscoring what Aristotle originally observed: that in rational explanation there can be no infinite regress.

Anticipating or perhaps inciting future intellectual chaos, Hume writes “[inductive] arguments must be probable only.” But is it really merely probable that touching a hot stove will burn rather than freeze your hand? What should we mean by “probable?” Should it be used as a paranoid hedge against our active imaginations? No: when all the evidence points in the same direction and none away then we should be confident, and reserve this hedging language for when it is actually called for, which as it turns out, is often.

Channeling Kant, Hume says that “In vain do you pretend to have learned the nature of bodies from your past experience.” Does this include Hume’s own learning of the nature of what you have learned? This message is inconsistent with what he has written elsewhere, which is that what we mean by “learned the nature of” is precisely observing a constant conjunction. He continues with “Their secret nature, and consequently, all their effects and influence, may change, without any change in their sensible qualities”, but in order to know they “may change” he would have to have learned from past experience, which he just prohibited. Hume’s failure to fully understand the axiomatic status of induction occasionally leads him to such absurdities.

He writes “When a child has felt the sensation of pain from touching the flame of a candle, he will be careful not to put his hand near any candle; but will expect a similar effect from a cause… If you assert, therefore, that the understanding of the child is led to this conclusion by any process of argument or ratiocination, I may justly require you to produce that argument…” Here Hume wishes to know how it is we can reasonably infer from experience. Ordinarily, people do not “reasonably” (in the sense of complete philosophic justification) do anything. A child trusts his own experience naturally, not reasonably. But there is a difference between child and scientist, so once we have answered that a child trusts because of Habit, we should ask why the case is any different for a scientist.

The answer is: integration. This does not introduce a new aspect at the foundation – even a scientist is at the mercy of Nature’s actual behaviors, and may not receive from it any certified guarantees. But to systematically integrate is a new aspect and brings deeper wisdom and capacity to predict. When a child sees the Sun rise each morning and believes it will continue to rise, this is an entirely different sort of understanding than the scientist has. The scientist knows from a great context of knowledge that the Sun is an object in space, he knows why it rises in the morning, and he knows just how consequential it would be for it to not do so. For the Sun to not rise, it is not this mere effect that would be different, but entire bodies of knowledge standing for virtually unlimited experiences would have been proven false. So it is one thing for a barbarian to entertain the idea that the Sun won’t rise in the morning, but a qualitatively different sort of thing for a rational mind to do. For to treat effects as isolated is qualitatively different than intensively explaining and integrating them into a rational system. And this integration ultimately rests on the widest of philosophic axioms of existence: the principle of uniformity of nature. This principle cannot be contested without tacitly relying upon it (for otherwise no conversation, which is itself physical artifact, could be comprehended), so it too is an axiom.

[link]Section 5 – Sceptical Solution of these Doubts[link]

I have no criticism to offer for this section, I only note that here Hume testifies in support of my own interpretation of his work as against his many misinterpreters:

“Nor need we fear, that this philosophy, while it endeavours to limit our enquiries to common life, should ever undermine the reasonings of common life, and carry its doubts so far as to destroy all action, as well as speculation. Nature will always maintain her rights, and prevail in the end over any abstract reasoning whatsoever. Though we should conclude, for instance, as in the foregoing section, that, in all reasonings from experience, there is a step taken by the mind, which is not supported by any argument or process of the understanding; there is no danger, that these reasonings, on which almost all knowledge depends, will ever be affected by such a discovery. If the mind be not engaged by argument to make this step, it must be induced by some other principle of equal weight and authority; and that principle will preserve its influence as long as human nature remains the same.” [emphasis mine]

[link]Section 6 – Of Probability[link]

I have no criticism to offer for this section.

[link]Section 7 – Of the Idea of Necessary Connexion[link]

Here Hume repudiates the notion that there is any certifiable guarantee that the same effects will always in infallibly follow from the same causes; at bottom, we merely observe and then expect the repeatability, without any part of any observation carrying any kind of guarantee. We utterly rely on Nature, there are no supernatural guarantees.

Hume impugns moral reasoning as less exact than mathematical but as I have argued in REASON and LIBERTY, mathematical reasoning is a species of moral reasoning.

Hume claims we never learn the “secret connexion” that binds cause to effect, and at any frontier of knowledge this is true, but it is overstating things if not technically then by omission (the difference in kind of scientific, integrated knowledge), for we do find that brain actuates limbs by means of nerves; that nerves work by means of synapses, etc. This is knowledge that was “secret” at one time but now is not (but clearly, beneath that lies more “secret” knowledge, which we may yet discover, up to a limit that no one may prescribe.) The rational understanding of “necessary connexion” results from 1) the uniformity of nature; 2) institutional integration of knowledge. But this is not a “guaranteed connexion” – there is no higher authority than Nature, and we are only its fallible interpreters.

It is thus not one mere instance nor merely a succession of instances that gives to us “connexion”, but rather their relation and integration to an ocean of experience, including not merely our own but everyone else’s as well.

When we say “cause” we can only mean either 1) this impression has always been followed by that one; 2) upon seeing this impression we always anticipate that one. Which is to say not that we can’t know, but that the mind is utterly subordinate to Nature, that knowledge may only be reliably acquired through a recognition of this subordination (also see Francis Bacon’s Novum Organum). Hume demonstrates that all knowledge is alike in its subordination to Nature, that no authority is higher than or different in principle from the constant observation that this follows from that.

[link]Section 8 – Of Liberty and Necessity[link]

This section is noteworthy for again affirming my interpretation of Hume as against his misinterpreters:

“Our idea, therefore, of necessity and causation arises entirely from the uniformity, observable in the operations of nature…”

“The vulgar, who take things according to their first appearance, attribute the uncertainty of events to such an uncertainty in the causes as makes the latter fail their usual influence… But philosophers, observing, that, almost in every part of nature, there is contained a vast variety of springs and principles, which are hid, by reason of their minuteness or remoteness, find, that it is at least possible the contrariety of events may not proceed from any contingency in the cause, but from the secret operation of contrary causes. This possibility is converted into certainty by farther observation; when they remark, that, upon an exact scrutiny, a contrariety of effects always betrays a contrariety of causes, and proceeds from their mutual opposition. A peasant can give no better reason for the stopping of any clock or watch than to say that it does not commonly go right: But an artist easily perceives, that the same force in the spring or pendulum has always the same influence on the wheels; but fails of its usual effect, perhaps by reason of a grain of dust, which puts a stop to the whole movement. From the observation of several parallel instances, philosophers form a maxim, that the connexion between all causes and effects is equally necessary, and that its seeming uncertainty in some instances proceeds from the secret opposition of contrary causes.”

Vulgar indeed is how we should describe the philosophy profession, which has so grossly distorted Hume!

  1. I am not Hume’s sole defender, a minority of academics agree with me that Hume Is Not A Skeptic about Induction, for instance, Xinli Wang.

  2. http://webspace.ship.edu/cgboer/psychbeginnings.html