Hume Shifts
the Burden of Proof

After all, it was over 250 years ago that Hume observed that "the rules of morality are not the conclusion of our reason." Yet Hume's claim has not sufficed to deter most modern rationalists from continuing to believe -- curiously enough often quoting Hume in their support -- that something not derived from reason must be either nonsense or a matter for arbitrary preference, and, accordingly, to continue to demand rational justifications.

F.A. Hayek, The Fatal Conceit, The Errors of Socialism [University of Chicago Press, 1988, 1991, p.66]

Every one knows that judicious matter and charms of style have rendered Hume's history [of England] the manual of every student. I remember well the enthusiasm with which I devoured it when young, and the length of time, the research and reflection which were necessary to eradicate the poison it had instilled into my mind. It was unfortunate that he first took up the history of the Stuarts, became their apologist, and advocated all their enormities... Although all this is known, he still continues to be put into the hands of all our young people, and to infect them with the poison of his own principles of government. It is this book which has undermined the free principles of the English government, has persuaded readers of all classes that these were usurpations on the legitimate and salutary rights of the crown, and has spread universal toryism over the land.

Thomas Jefferson, "To Colonel William Duane," August 12, 1810, The Life and Selected Writings of Thomas Jefferson, edited and with an Introduction by Adrienne Koch and William Pedan [The Modern Library, Random House, 1944, 1972, 1993, p.555, boldface added]

Allein das der Metaphysik von je her ungünstige Schicksal wollte, daß er von keinem verstanden würde. Man kann es, ohne eine gewisse Pein zu empfinden, nicht ansehen, wie so ganz und gar seine Gegner Reid, Oswald, Beattie, und zuletzt noch Priestly, den Punkt seiner Aufgabe verfehlten, und, indem sie immer das als zugestanden annahmen, was er eben bezweifelte, dagegen aber mit Heftigkeit und mehrenteils mit großer Unbescheidenheit dasjenige bewiesen, was ihm niemals zu bezweifeln in den Sinn gekommen war, seinen Wink zur Verbesserung so verkannten, daß alles in dem alten Zustande blieb, als ob nichts geschehen wäre. Es war nicht die Frage, ob der Begriff der Ursache richtig, brauchbar, und in Ansehung der ganzen Naturerkenntnis unentbehrlich sei, denn dieses hatte Hume niemals in Zweifel gezogen; sondern ob er durch die Vernunft a priori gedacht werde, und, auf solche Weise, eine von aller Erfahrung unabhängige innre Wahrheit, und daher auch wohl weiter ausgedehnte Brauchbarkeit habe, die nicht bloß auf Gegenstände der Erfahrung eingeschränkt sei: hierüber erwartete Hume Eröffnung. Es war ja nur die Rede von dem Ursprunge dieses Begriffs, nicht von der Unertbehrlichkeit desselben im Gebrauche.

But Hume suffered the usual misfortune of metaphysicians, of not being understood. It is positively painful to see how utterly his opponents, Reid, Oswald, Beattie, and lastly Priestly, missed the point of the problem: for while they were ever taking for granted that which he doubted, and demonstrating with zeal and often with impudence that which he never thought of doubting, they so misconstrued his valuable suggestion that everything remained in its old condition, as if nothing had happened. The question was not whether the concept of cause was right, useful, and even indispensible for our knowledge of nature, for this Hume had never doubted; but whether that concept could be thought by reason a priori, and consequently whether it possess an inner truth, independent of all experience, implying a perhaps more extended use not restricted merely to objects of experience. This was Hume's problem. It was solely a question concern the origin, not concerning the indispensable need of using the concept.

Immanuel Kant, Prolegomena to Any Future Metaphysics, translated by Lewis White Beck [The Library of the Liberal Arts, Bobbs-Merrill Company, 1950, p.7]; «Prolegomena zu einer jeden künftigen Metaphysik», Werkausgabe V, Schriften zur Metaphysik und Logik I [Suhrkamp Taschenbuch Wissenschaft, Insel Verlag Wiesbaden, 1958, p.116-117]; color added.

At the beginning of his Enquiry Concerning Human Understanding, David Hume, having argued that all ideas come from antecedent impressions, describes a test of his theory:

Those who would assert that this position is not universally true nor without exception, have only one, and that an easy method of refuting it; by producing that idea, which, in their opinion, is not derived from this source. It will then be incumbent on us, if we would maintain our doctrine, to produce the impression, or lively perception, which corresponds to it. [Shelby-Bigge edition, Oxford, 1902, 1972, pp. 19-20]

Here the challenge and the burden of proof is clear enough: If we produce an idea that we contend is not derived from an original impression, or lively perception, then it is Hume's business to produce that impression or admit that his theory, his empiricism, is not correct.

The difficulty with this test for Hume is that he himself discovers many ideas which evidently have not been derived from an original impression. Thus, later in the same Enquiry, we find Hume saying:

There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connection.... [pp.61-62]

When we look about us towards external objects, and consider the operation of causes, we are never able, in a single instance, to discover any power or necessary connection; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other.... Consequently, there is not, in any single, particular instance of cause and effect, any thing which can suggest the idea of power or necessary connection. [p. 63]

...but the power or force, which actuates the whole machine [the universe], is entirely concealed from us, and never discovers itself in any of the sensible qualities of body.... It is impossible, therefore, that the idea of power can be derived from the contemplation of bodies, in single instances of their operation; because no bodies ever discover any power, which can be the original of this idea. [pp. 63-64]

Now, in terms of Hume's own challenge, one might say that he has discovered several ideas that refute his empiricism. However, he has already protected himself against such refutation: Having proposed his test, Hume almost immediately took it back and shifted the burden of proof:

When we entertain, therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but too frequent), we need to enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will serve to confirm our suspicion. [p. 22]

Now if we produce an idea, like power or necessary connection, that we maintain is not derived from an antecedent impression, it is not incumbent upon Hume to produce the impression or abandon his empiricism. Instead, Hume can say this means that our idea is "without any meaning or idea." This is indeed what Hume says:

And as we can have no idea of any thing which never appeared to our outward sense or inward sentiment, the necessary conclusion seems to be that we have no idea of connection or power at all, and that these words are absolutely without any meaning, when employed either in philosophical reasonings or common life. [p. 74, boldface added]

This is the beginning of an evil tradition in the history of philosophy to dismiss many perfectly sensible terms in philosophy and ordinary language as "meaningless" according to some new philosophical theory of meaning.

Intentionally or not, Hume's shifting of the burden of proof serves to protect his theory from refutation, according to the obvious avenue of refutation that he had just recognized himself. Such a theory simply begs the question, and it is hard to imagine that an acute thinker like Hume would fail to recognize that. In any case, having incautiously offered the terms of his test, he quickly enough prepared the way for his rejection of inconvenient concepts.

Even so, Hume doesn't quite dismiss the ideas of "power, force, energy or necessary connection" as "without any meaning or idea." He better not; for power, force, and energy especially are not "obscure and uncertain" concepts from metaphysics: They all have clear and useful definitions in physics. "Force" had already been defined by Isaac Newton himself in the famous equation, F=ma -- force equals mass times acceleration. But Hume can never recover from his presuppositions that because there is no impression, we cannot know that there is anything there in nature. So, the best that Hume can do is to attribute our belief in power, force, energy, and necessary connection to the psychological conditioning brought about by the "custom" or "habit" of experiencing the constant conjunction of causes with effects:

This connexion, therefore, which we feel in the mind, this customary transition of the imagination from one object to its usual attendant, is the sentiment or impression from which we form the idea of power or necessary connection. Nothing farther is in the case. [p. 75]

Although Hume may think that he has formally met his challenge to account for the ideas of power and necessary connection, his answer has the drawback of no longer being about the world, but just about the operations of the mind. If we reject this answer as being irrelevant to knowledge, committing a material fallacy of relevance, and we hold him to a ground of knowledge in objects, then he can only say that "we have no idea of connexion or power at all, and that these words are absolutely without any meaning..."

The subjective approach through psychological "habit" has several important consequences:

  1. Only concepts that relate to the objects of experience, albeit without corresponding to "impressions" themselves, can be saved. Thus, although causality, force, and the like can be saved for physics, moral concepts like free will, or religious concepts like God or the soul, cannot be saved. They will truly be for Hume "without any meaning or idea." However, since Hume himself views the convictions of custom and habit as perhaps wise provisions of Nature against the imperfections and uncertainties of our reason, there is in principle no reason why Nature should not also have provided us with convictions that do not relate directly to perceptual objects in the manner identified by Hume. If Hume is offering up a description of human nature, he obviously overlooks the circumstance that human nature in all times and places has tended to turn to religious expression. Hume actually edits "human nature" according to his own Scottish and Epicurean preferences. Kant, who also limits theoretical knowledge to the world of experience, nevertheless allows "postulates of practical reason" for moral or religious issues that do not relate directly to scientific knowledge.

  2. The certainty that Hume attributes to the necessary connection of causality and the laws of nature has been a matter of confusion ever since. Since our own psychological certainty obviously has nothing to do with any necessity among the objects of nature, it is easy to infer that Hume did not believe there was any certainty. It should then be surprising to find how easily Hume rules out, not just miracles, but also free will and even chance just because all would involve violations of causality, as he understands it. This goes back to the kind of Skeptic that Hume is, not a Pyrrhonian, who suspends all judgment because of lack of objective knowledge, but an Academic Skeptic, who continues making the reasonable judgments of ordinary life, regardless of lack of objective knowledge -- these differences were already sorted out in Hellenistic philosophy. Hume's subjective certainty as a Skeptic is thus just as strong as the certainty of those who might believe in objective necessity among objects:  Indeed, Hume's certainty often seems greater; for it does not follow from a belief in necessity among objects that there should be certainty in beliefs about them, and anyone who believes in necessity among objects can easily be more sceptical than Hume, in the ordinary sense, about what those necessities are. There are thus two false inferences to guard against: (1) that Hume was "uncertain" about his beliefs because he knew that experience could not justify them; and (2) that we should deny necessity among objects just because we are uncertain about our beliefs. Hume's own certainty, indeed, rises to the level of dogmatism, disparaging, not just the "superstition" of Roman Catholicism, but even attacking geometry, along with metaphysics, for the problems of infinite divisibility. [Note]

  3. Hume's attack on geometry is instructive:

    No priestly dogmas, invented on purpose to tame and subdue the rebellious reason of mankind, ever shocked common sense more than the doctrine of the infinite divisibility of extension, with its consequences; as they are pompously displayed by all geometricians and metaphysicians, with a kind of triumph and exultation. [p. 156]

    Although Hume has already said, "Though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retain their certainty and evidence" [p. 25], he must turn against geometry where it conflicts with his empiricism: Quantities too small to be seen correspond to no "impression" and are thus "without any meaning or idea." The division of such quantities into even smaller quantities is that much the worse. Unfortunately for Hume, his attack here cannot just be on "geometricians and metaphysicians," it must also be on physicists, for Newton's calculus of infinitesimal quantities is part of the geometry of infinite divisibility. It might be argued, indeed, that an infinitesimal is something that is the result of a finite division; but it is also certainly something that is not a discernible quantity, which must necessarily offend Hume's empiricism. "Too small to be detected, but there" is not a formula for Empiricist mathematics. Perhaps Hume did not notice, as Berkeley did, that his epistemological presuppositions might put him on a collision course with a modern physics dependent on many mathematical ideas that have "shocked common sense."

  4. The attack on geometry is a clue to something larger: Hume's empiricism, while ruling out various metaphysical entities (free will, the soul, God, etc.), to the applause of his many admirers, also ruled out many of the future developments of science, which few admirers this side of deconstruction are likely to applaud:

    Our senses inform us of the colour, weight, and consistence of bread; but neither sense nor reason can ever inform us of those qualities which fit it for the nourishment and support of a human body. [p. 33]

    These ultimate springs and principles [of events in nature] are totally shut up from human curiosity and enquiry. Elasticity, gravity, cohesion of parts, communication of motion by impulse[sic]; these are probably the ultimate causes and principles which we shall ever discover in nature. [p. 30]

    The course of science in the 19th and 20th centuries would have astonished Hume, as it certainly discredits the foundation of his predictions for the future of human knowledge. That proteins, vitamins, carbohydrates, minerals, etc. explain the basis of human nutrition, and that electromagnetism and atomic, nuclear, and particle physics explain much of the fundamental behavior of matter, are not just things that escaped Hume's imagination -- they escaped everyone's imagination until the discovery of them was effected -- but they are things that occupy a cognitive space whose very existence Hume explicitly denied: They do not correspond to "impressions" any more than God or the soul do. By Hume's criterion they are "without any meaning or idea." In turn, "impulse" is the theory of motion introduced by John Philoponus in the 6th century, which was replaced by Galileo and Newton with the modern theory of forces and momentum. Hume isn't quite up to date on his physics.

Thus, when Hume shifts the burden of proof to protect his empiricism, he shuts off any possible understanding, not just of metaphysics and religion, but of much of mathematics and science. That is a price some, like Wittgenstein and Rorty, are still willing to pay: That mathematics and science really tell us nothing about the world but are elaborate tricks we have devised that unaccountably produce results that we want in practical matters. Such a dismal aspiration can be found to have motivated few, if any, historic scientists. As Roger Penrose says in a footnote to The Emperor's New Mind:

I have taken for granted that any 'serious' philosophical viewpoint should contain at least a good measure of realism. It always surprises me when I learn of apparently serious-minded thinkers, often physicists concerned with the implications of quantum mechanics, who take the strongly subjective view that there is, in actuality, no real world 'out there' at all! The fact that I take a realistic line wherever possible is not meant to imply that I am unaware that such subjective views are often seriously maintained -- only that I am unable to make sense of them. [p. 299]

The desire to know that drove Galileo, Newton, or Einstein cannot be addressed by a philosophical theory of knowledge that denies that any such knowledge can be had. No one who thought that "knowledge" was simply a "device for calculation" would bother to spend years in purely theoretical research; nor would anyone bother to trouble themselves with all the difficulty of mathematical study and scientific research if they believed the next step in nihilistic theory, that scientific "knowledge" is an arbitrary construction of power relationships. In that case, "knowledge" would tell us nothing either about the world or about practical results but simply would embody the power relationships that distribute goods according to the race, class, and gender construction built into it.

While Hume does not go as far as much more recent theory, it is rarely recognized, as it was by Kant, that he shut off much of science as well as religion with his empiricism. Since many great defenders and devotees of science in the 20th century, like the Logical Positivists, thought that Hume's philosophy was very nearly sufficient for a proper philosophy of science, this has been a very dangerous oversight. But this whole direction of error can be forestalled just by noticing the trick at the very beginning: An "idea" without an "impression" is not to be dismissed as "without any meaning" but is actually counter-evidence against Hume's whole empiricism. Until Hume shifts the burden of proof, his own work provides some of the best evidence against empiricism, as Kant himself appreciated.

When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.

This famous passage, which ends the Enquiry Concerning Human Understanding [op.cit. p.165], with its rather chilling call for book burning, starkly exposes the kind of petard upon which Hume's own project is hoist; for Hume's own books, including the Enquiry and the Treatise both, contain no mathematics or experimental science. By his own criteria, they are thus to be committed to the flames. To be sure, Hume thought that he was doing empirical "experiments" in his books; but he was confused about this and has never really been considered a scientist by anyone. No, he is a philosopher, discussing the form and implications of an Empiricist theory of knowledge. He therefore paints himself into the same corner as any philosopher advocating scientism or positivism, that his own theory rules out the possibility or meaning of his own theory. This would become an occupational hazard in some of his spiritual successors. The Logical Positivists could never admit the absurdity of the doctrine of their school on the basis of the principles of that very doctrine. The younger Wittgenstein did recognize that the Tractatus was nonsense in terms of its own theory, but then the older Wittgenstein, abandoning scientism, nevertheless did not admit that his later theory was not ordinary language, which for him became normative, but was actually a "private language," whose possibility he denied.

Hume and all these successors thus cannot escape an accusation that could easily have been made by either Socrates or Kant:  that they insensibly practice metaphysical thinking and appeal to metaphysical principles even when they do not think they are doing so and even while they try to argue against the possibility of such things. As Plato said of Protagoras, they thus manage to refute themselves.

Confusions about Hume in Antony Flew

On Miracles

Key Distinctions for Value Theories, and the Importance of Hume

Substance and Essence

A Lecture on the Good


History of Philosophy

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Hume Shifts the Burden of Proof, Note;
Confusions about Hume in Antony Flew

I have found a very explicit demonstration of common confusions about Hume in a recent book, There Is A God, by Antony Flew [HarperOne, 2007]. Flew himself was the product of the linguistic "Oxford Philosophy" of his supervisor, the infamous (in my eyes) Gilbert Ryle. As it happens, Flew's book recounts his transformation from a militant and notorious atheist to a deist (or something -- he favorably references many theistic arguments, some of which seem incompatible with deism, i.e. the doctrine of an impersonal God who now leaves the world alone to follow the mechanical laws that God with infinite prescience designed at the beginning); but we also get some retrospective on the analytic tradition of philosophy he has always represented, a tradition that purportedly reveres, and can certainly be expected to understand, Hume. Yet Flew says:

Hume denied causation in the first Inquiry [sic -- should be "Enquiry"] and claimed that all the external world really contains is constant conjunctions; that is, events of this sort are regularly followed by events of that sort. We notice these constant conjunctions and form strong habits associating the ideas of this with the ideas of that. We see water boiling when it is heated and associate the two. In thinking of real connections out there, however, we mistakenly project our own internal psychological associations. Hume's skepticism about cause and effect and his agnosticism about the external world are of course jettisoned the moment he leaves his study. Indeed, Hume jettisions all of his most radical skepticism even before he leaves his study. There is, for instance, no trace of the thesis that causal connections and necessity are nothing but false projections onto nature in the notorious section "Of Miracles" in the first Inquiry. [p.58, boldface added]

Each of the expressions that I have quoted in boldface represents a misunderstanding of Hume, something which must go back to Flew's failure to appreciate the difference, cited by Hume himself, between a Pyrrhonian and an Academic Skeptic. Thus, Hume never "denied causation" but simply argued that it was not the result of any rational inferences based on instances of perception. This meant that Hume never asserted that the "external world" contained nothing but constant conjunctions. Such an assertion would be no kind of Skepticism. Similarly, Hume would never assert that we "mistakenly" project our internal psychological associations onto the world.

Indeed, Hume holds in mind a possible objective ground of the subjective associations, namely Human Nature, to which the title of his first book makes reference. He reflects in the Enquiry that it is probably better for our survival if our knowledge of cause and effect is produced instinctively by association than by some fallible chain of rational inferences from objective knowledge. It is hard to imagine that Flew actually overlooked this whole dimension of Hume's philosophy. But he did. Indeed, Flew writes as though in his youth he accepted without qualification that Hume "denied causality," while later in the perspective of mature reflection he realized that Hume "jettisoned" his Skepticism in regard to various applications. However, Hume never denied causality nor was he so careless as to inconsistently allow causality in order to deny miracles, etc. Flew's mature reflection still hasn't gotten it quite right.

No one who has noticed Hume's explicit assertion that none of his Skepticism will have any effect on ordinary practice, or that after philosophical reflection we still leave the room by the door and not by the window, would be surprised, as Flew is, that even in his study Hume rejects chance, free will, and miracles all because they violate causality. Flew's statement that "causal connections and necessity are nothing but false projections" shows how badly he, and probably most of his teachers and colleagues, construed Hume's philosophy.

My practice, you say, refutes my doubts. But you mistake the purport of my question. As an agent, I am quite satisfied in the point; but as a philosopher, who has some share of curiosity, I will not say scepticism, I want to learn the foundation of this inference [i.e. from cause to effect]. No reading, no enquiry has yet been able to remove my difficulty, or give me satisfaction in a manner of such importance. Can I do better than propose the difficulty to the public, even though, perhaps, I have small hopes of obtaining a solution? We shall at least, by this means, be sensible of our ignorance, if we do not augment our knowledge. [An Enquiry Concerning Human Understanding, op.cit., p.38, boldface added]

Nor need we fear that this [Sceptical] 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. [ibid., p.41, boldface added]

Hume says, "There is, indeed, a more mitigated scepticism or academical philosophy, which may be both durable and useful, and which may, in part, be the result of this Pyrrhonism, or excessive scepticism, when its undistinguished doubts are, in some measure, corrected by common sense and reflection" [ibid., p.129, boldface added]. "The great subverter of Pyrrhonism or the excessive principles of scepticism is action, and employment, and the occupations of common life" [p.126].

Kant already understood Hume better than Hume's contemporary critics or his own later Analytic admirers, like Antony Flew or Gilbert Ryle. Hence Kant famously says:

But Hume suffered the usual misfortune of metaphysicians, of not being understood. It is positively painful to see how utterly his opponents, Reid, Oswald, Beattie, and lastly Priestley, missed the point of the problem; for while they were ever taking for granted that which he doubted, and demonstrating with zeal and often with impudence that which he never thought of doubting, they so misconstrued his valuable suggestion that everything remained in its old condition, as if nothing had happened. The question was not whether the concept of cause was right, useful, and even indispensable for our knowledge of nature, for this Hume had never doubted; but whether that concept could be thought by reason a priori, and consequently whether it possessed an inner truth, independent of all experience, implying a perhaps more extended use not restricted merely to objects of experience. This was Hume's problem. It was solely a question concerning the origin, not concerning the indispensable need of using the concept. Were the former decided, the conditions of the use and the sphere of its valid application would have been determined as a matter of course. [Prolegomena to Any Future Metaphysics, p.259, translated by Lewis White Beck, Library of the Liberal Arts, 1950, pp.6-7, boldface added].

Kant's comment is often quoted, but it cannot be properly understood if the confusions of Flew's tradition stand in the way. They exemplify Kant's point.

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