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Hume’s Understanding of Understanding

  • Hume 1 – Enquiry

    "David Hume," by Mitch Francis

    “David Hume,” by Mitch Francis


    Painting of David Hume

    Painting of David Hume

    David Hume (1711-1776) was a Scottish philosopher, more famed in his day for his History of England than for his philosophical work on knowledge. As an empiricist, Hume traced the sources of knowledge to experience – as opposed, for instance, to Plato’s account of real knowledge as knowledge of Forms which exist in a realm beyond experience. The following discussion and excerpts are based on Hume’s 1748 An Enquiry Concerning Human Understanding.

    Hume distinguished impressions (such as a perception of the glaring sun or the feeling of rising anger) from ideas (such as a recollection of the sun, or the thought that I might “blow my top”), less lively “copies” of impressions. He argued that all ideas are copies of materials encountered in experience. We have here, Hume thus argued, a principle for by-passing much nonsense.

    When we entertain therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but too frequent), we need but enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will serve to confirm our suspicion. By bringing ideas into so clear a light we may reasonably hope to remove all dispute, which may arise, concerning their nature and reality.

    Does anyone claim impressions of the soul? of God? of Plato’s Form of the Good? These, then, were suspect for Hume.

    Hume recognized only two types of knowledge: what is known to be true as a matter of concepts (what he called “relations of ideas,” such as that triangles have three sides) or what is a matter of experience (which he called, somewhat confusingly to modern ears, “matters of fact”). The latter include things we purport to know based on experience, and not on concepts alone – for instance, that November 28, 2012 is the date of a lunar eclipse, or even that the sun will rise tomorrow.

    Notice that much of our most cherished “knowledge” is a matter of experience – such as that Mom loves me, that Bob Marley was a Rastafarian, that our planet is warming. So Hume investigated this type more deeply. What is the basis of such “knowledge”? Hume claimed that in every case, the reasoning that supports such propositions is cause-effect reasoning. “By means of that relation alone we can go beyond the evidence of our memory and senses.” Why believe that Mom loves me? It’s because of the causal connection I suppose to hold between her inner state and what I experience (she says, “I love you” and shows care). The connection is that of cause and effect. Why believe that Joe is in Spain? It’s because of the connection I suppose to hold between his location and the postmark from Salamanca on the card he sent. Cause and effect.

    A probing philosopher, it’s not surprising that Hume’s spade broke deeper ground: “If we would satisfy ourselves, therefore, concerning the nature of that evidence, which assures us of matters of fact, we must enquire how we arrive at the knowledge of cause and effect.” It cannot, he argued, be known “by reasonings a priori,” which means “by thinking that is uninformed by experience.”

    Adam, by Lucas Cranach the Elder

    Adam, by Lucas Cranach the Elder (16th century, German Renaissance).

    “Knowledge” of cause and effect is not derived from reason alone.

    Let an object be presented to a man of ever so strong natural reason and abilities; if that object be entirely new to him, he will not be able, by the most accurate examination of its sensible qualities, to discover any of its causes or effects. Adam, though his rational faculties be supposed, at the very first, entirely perfect, could not have inferred from the fluidity and transparency of water that it would suffocate him, or from the light and warmth of fire that it would consume him…. nor does any man imagine that the explosion of gunpowder, or the attraction of a loadstone, could ever be discovered by arguments a priori….

    We fancy, that were we brought on a sudden into this world, we could at first have inferred that one Billiard-ball would communicate motion to another upon impulse; and that we needed not to have waited for the event, in order to pronounce with certainty concerning it. Such is the influence of custom, that, where it is strongest, it not only covers our natural ignorance, but even conceals itself, and seems not to take place…. When I see, for instance, a Billiard-ball moving in a straight line towards another; even suppose motion in the second ball should by accident be suggested to me, as the result of their contact or impulse; may I not conceive, that a hundred different events might as well follow from that cause? May not both these balls remain at absolute rest? May not the first ball return in a straight line, or leap off from the second in any line or direction? All these suppositions are consistent and conceivable.

    “Knowledge” of cause and effect must thus be derived from experience. How well does experience support such “knowledge”?

    So the only remaining possibility is that we arrive at such “knowledge” based on experience – not abstract reasoning, but on our recollection of things past. In a thousand similar circumstances, I have witnessed one moving object colliding with another, and it is on those experiences that I base my expectations pertaining to this Billiard-ball:


    all inferences from experience suppose, as their foundation, that the future will resemble the past, and that similar powers will be conjoined with similar sensible qualities.

    This is often called the “Principle of the Uniformity of Nature.”

    If there be any suspicion that the course of nature may change, and that the past may be no rule for the future, all experience becomes useless, and can give rise to no inference or conclusion.

    Thus, so much of our most cherished “knowledge” depends upon this Principle of Uniformity. Wouldn’t it be nice, then, if we could provide a rational argument in favor of it? One might even think that task is required to provide an adequate justification of our knowledge, to prove we’re not just spellbound by “shadows on the wall.” But this is where Hume was most revolutionary. On the one hand, he denied that this principle could be proved in the manner of “relations of ideas,” like a truth of definition, arithmetic, or geometry could. On the other hand, that left only experience to which to appeal.

    It is impossible… that any arguments from experience can prove this resemblance of the past to the future; since all these arguments are founded on the supposition of that resemblance. Let the course of things be allowed hitherto ever so regular; that alone, without some new argument or inference, proves not that, for the future, it will continue so.

    Hence, Hume became one of the most renowned doubters in history, arguing that this foundational principle is unprovable, and human knowledge is left in mid-air, as it were. We don’t argue to the Principle of Uniformity so much as through it. In effect, he pointed out an unnoticed flaw in our certainty. Consider the following argument in favor of the Principle:

    Premiss: The future’s been like the past in the past.

    Conclusion: So the future’ll be like the past in the future.

    Compare to this circular argument:

    Premiss: According to Consumer Reports, the most reliable consumer magazine is Consumer Reports.


    Conclusion: So the most reliable consumer magazine is Consumer Reports.

    The conclusion only follows logically if Consumer Reports is reliable; but that is precisely what this argument aims to establish. Assuming the reliability is “viciously circular.”

    Is it a strong argument? Hume showed why it is not: The premiss does not justify the conclusion unless we assume the Principle of Uniformity. But that is precisely what was to be proved! Hence, this effort to solidify our knowledge is circular, leaving much of our cherished knowledge in question.

    At this point, one might wonder whether Hume is hypocritical. After all, he presumably supposes his chair will support him, just as it always did in the past; he presumably believes the bread will nourish him, and that the sun will rise tomorrow, just like always. He enters the plea, “Not guilty,” and clarifies:

    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. No reading, no enquiry has yet been able to remove my difficulty, or give me satisfaction in a matter 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?

    No one has yet responded to Hume effectively on this issue, although many continue to spill ink in response to his challenge.


    Where does this leave us? What rationally demonstrable principle, then, governs our cherished “knowledge”? Hume’s conclusion was that the governing principle was not a child of reason after all:

    This principle is Custom or Habit…. Perhaps we can push our enquiries no farther, or pretend to give the cause of this cause; but must rest contented with it as the ultimate principle, which we can assign, of all our conclusions from experience. It is sufficient satisfaction, that we can go so far, without repining at the narrowness of our faculties because they will carry us no farther. And it is certain we here advance a very intelligible proposition at least, if not a true one, when we assert that, after the constant conjunction of two objects — heat and flame, for instance, weight and solidity — we are determined by custom alone to expect the one from the appearance of the other. This hypothesis seems even the only one which explains the difficulty, why we draw, from a thousand instances, an inference which we are not able to draw from one instance, that is, in no respect, different from them. Reason is incapable of any such variation. The conclusions which it draws from considering one circle are the same which it would form upon surveying all the circles in the universe. But no man, having seen only one body move after being impelled by another, could infer that every other body will move after a like impulse. All inferences from experience, therefore, are effects of custom, not of reasoning.

    Custom, then, is the great guide of human life.

    Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past…. All these operations are a species of natural instincts, which no reasoning or process of the thought and understanding is able either to produce or to prevent.

    Contrary to Plato and Descartes, who celebrated the prospect of humanity’s ascent to quite lofty knowledge and freedom from our “lower nature,” Hume uncovered a new way in which instinctual “animal-nature” is also very much a part of our humanity.

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