An Enquiry Concerning Human Understanding

“Reading Hume is like driving a new Maserati down a dead end street.” – Taylor Swift

I will admit I found a kind of allure in Hume’s work, when I had some distance from it. An Enquiry Concerning Human Understanding was engaging and lucid, even if I was quite unhappy with where we ended up at its conclusion. But having promised a less critical post to Tosha… well, Hume, yeah I think you’re cute, but I feel like you should know… I’m not the kind of girl to get messed up with you.

Hume’s empiricism seems to spawn or found the rest of his philosophy, and so it is his empiricism I will attempt to understand. I will consider his phenomenological account of of our perceptions, and the epistemology it entails, and if I don’t get too tired, I might look at Humean scepticism and/or his idea of philosophers*.

For Hume, our experience is made up of ideas (or thoughts) and impressions**. Ideas are the weaker of the two classes of perceptions, and Hume acknowledges the general view that ‘nothing… may seem more unbounded than the thought of man,” i.e. that man can create ideas of many different things, including things he has not had impressions of; this is a mistaken belief: “all our ideas or more feeble perceptions are copies of our impressions or more lively ones.” All ideas we have arise from our impressions of things, even if sometimes we separate, join, inflate, or deflate different ideas to make them into something new (such as joining the head and torso of a man with the body of horse to form the idea of a centaur).

Hume provides an example of an exception to this, one that has become infamous: A man who has seen a range of shades of blue – all shades of blue, except one, in fact. Hume acknowledges that though the man has never had an impression of this shade of blue, he may form an idea of it. However, “this instance is so singular, that it is scarcely worth our observing, and does not merit, that for it alone we should alter our general maxim.” Clearly the issue is not so straightforward as Hume might wish us to believe, or perhaps even  more simplistic than he lets on.  I am inclined to think that Hume has provided us with an example that is not really a contradiction of his ‘general maxim.’ Similar to the way Hume describes how we come to have an idea of God – by “reflecting on the operations of our own mind, and augmenting, without limit, those qualities of goodness and wisdom” – so to can one “augment” ideas of impressions of colors, in order to form an idea of a new or different shade. In fact, it might seem unclear that ideas, faint as they are, would be so accurate as to not mistakenly imagine a color one had never had an impression of. (see the link above for a more thorough discussion of this problem)

Hume writes: “All ideas, especially abstract ones, are naturally faint and obscure: The mind has but a slender hold of them: They are apt to be confounded with other resembling ideas; and when we have often employed any term, though without a distinct meaning, we are apt to imagine it has a determinate idea, annexed to it. On the contrary, all impressions, that is, all sensations, either outward or inward, are strong and vivid: The limits between them are more exactly determined: Nor is it easy to fall into any error or mistake with regard to them.”

Hume’s understanding of perception as divided into ideas and impressions is then translated into two objects of human reason: “All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact.” Relations of ideas are intuitively or demonstratively certain; “propositions of this kind are discoverable by the mere operation of thought, without dependence on what is any where existent in the universe.” It is possible that a circle never existed in nature, but Euclid’s demonstrative proofs would remain certain.

Understanding matters of fact seems based in the relation of cause and effect: “I shall venture to affirm, as a general proposition, which admits of no exception, that the knowledge of this relation is not, in any instance, attained by reasoning a priori; but arises entirely from experience, when we find, that any particular objects are constantly conjoined with each other.” The opposite of any matter of fact is not logically contradictory; it is not reason that tells us the sun will rise tomorrow morning, for if the sun did not rise there would be no contradiction with reason. We assume the sun will rise tomorrow because it always has; we associate morning with the rising of the sun because in our experience it has always been that way.

Hume argues that we understand cause and effect through experience alone; reason will never provide an explanation of causation: “Who will assert, that he can give the ultimate reason, why milk or bread is proper nourishment for a man, not for a lion or a tiger?” What Hume is getting at is that there is nothing discoverable by reason about a piece of bread in itself that would explain why it provides nourishment. In fact, there is nothing about what we perceive to be cause and effect – that a rock falls when dropped, that fire burns upon close contact – which is known through reason; it is a belief formed entirely through experience.

When one one billiard ball hits another, stationary ball, we expect the first to transfer motion to the second. If someone throws a rock at our head, we expect it to hurt. But these beliefs are a result of the fact that every time in the past a rock has hit our heads, or one billiard ball has collided with another, the effect has been similar. There is no logical way to show that this time the effect will be the same. However, when a rock comes hurtling at your head, you move out of it’s way because frequent experience and testimony to the fact that a rock hitting you in the face will hurt has caused you to form a habit or custom that acts on the belief that getting hit in the face hurts: “We have said, that all arguments concerning existence are founded on the relation of cause and effect; that our knowledge of that relation is derived entirely from experience; and that all our experimental conclusions proceed up on the supposition, that the future will be conformable to the past.”

So it is experience, not reason, that leads me to believe that the sun will rise tomorrow, and that I will die alone because I tweet in Elvish. I operate successfully in the world because of the habits that I have acquired; I don’t expect things to hover in mid-air, or to not die when I walk in front of moving bus. But this doesn’t mean I know the reason for any of these effects, for “the powers and forces by which [nature] is governed, be wholly unknown to us.”

“In a word, then, every effect is a distinct event from its cause. It could not, therefore, be discovered in the cause, and the first invention or conception of it, a priori, must be entirely arbitrary  And even after it is suggested, the conjunction of it with the cause must appear equally arbitrary; since there are always many other effects  which, to reason, must seem fully as consistent and natural. In vain, therefore, should we pretend to determine any single event, or infer any cause or effect, without the assistance of observation and experience.”

If there is one thing this seems to have significant repercussions for, it is science. Hume asserts that “from causes, which appear similar, we expect similar effects. This is the sum of all our experimental conclusions.” We have seen already that metaphysics is essentially useless: reason and speculation can tell us little of the world and matters of fact, but ‘science’ – physics in particular – is then nothing but the sum of observations, and while it may have provided information by which we can make accurate judgments about the world and predictions for what will happen in the future, there is no certainty to this. For Hume, then, all of science relies on experiential understanding with no foundation in reason; there is no logical reason to believe that the principles of physics will be true*** in the next second, or minute, or year, or century. Of course, this seems a troublesome place to have arrived, especially for physicists (Peter!!!)****.

Hume goes on to argue that the idea of necessity is one we know only from the interaction of bodies in nature; that we see consistently similar effects from similar causes is how we come to understand the idea of necessity: “It seems evident, that, if all the scenes of nature were continually shifted in such a manner, that no two events bore any resemblance to each other, but every object was entirely new, without any similitude to whatever had been seen before, we should never, in that case, have attained the least idea of necessity, or of a connexion among these objects.” Indeed, the constancy of things in the world seems to be the basis of everything we understand (which seems quite obviously right), since without some constancy even “we” is an unintelligible concept. But no need to get further into the idea of necessity.

One question that must arise as one reads Hume’s epistemology is what difference there is then between the actions of humans and animals. Hume himself writes: “we may observe, that the animal infers some fact beyond what immediately strikes his senses; and that this inference is altogether founded on past experience, while the creature expects from the present object the same consequences, which it has always found in its observation to result from similar objects.” Hume responds by saying: 1. we significantly surpass the ability of animals in attention, memory and observation; 2. our greater minds are better able to comprehend the whole system of objects and their consequences; 3. we have observed that “one man is able to carry on a chain of consequences to a greater length than another;” 4. men often run in to confusion, but some much more frequently than others… Hume lists the differences between humans’ capacities of understanding, and uses these to then express the difference between human and animal. While I take no issue with the idea that humans and animals are on a spectrum of understanding, many others do (meat-eaters, I presume!).

Hume also places much value in the testimony of other men. In his lengthy section more or less refuting the possibility of miracles, he writes: “we may observe, that there is no species of reasoning more common, more useful, and even necessary to human life, than that which is derived from the testimony of men, and the reports of eye-witnesses and spectators.” For example, in the past, almost all of history testifies that when one dies, one is dead and stays dead. The fact that some hundred people claim to have seen a man rise from the dead, and use this as validation of their religious beliefs, should suggest to us that an alternative explanation – other than a man rising from the dead – is much more likely and reasonable. Moreover, it is because in all the history of the world, humans testify to seeing the sun rise in the morning, that we can trust in this experience. Hume goes on in great detail about miracles, but that is an issue for another blog.

I think that’s about enough Hume for today, which means, ominously, that I’m getting ever closer to reading Kant. Agh!

*”The mere philosopher is a character, which is commonly but little acceptable in the world, as being supposed to contribute nothing either to the advantage or pleasure of society; while he lives remote from communication with mankind, and is wrapped up in principles and notions equally remote from their comprehension… and though a philosopher may live remove from business, the genius of philosophy, if carefully cultivated by several, must gradually diffuse itself throughout the whole society, and bestow a similar correctness on every art and calling.”

**”The less forcible and lively are commonly denominated thoughts or ideas.”…”By the term impression, then, I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will.”

*** “This principle is custom or habit.”…”All inferences from experience, therefore, are effect of custom, not of reasoning.”…”Custom, then, is the great guide of human life.”…”Custom is that principle, by which this correspondence [nature and our ideas] has been effected; so necessary to the subsistence of our species, and the regulation of our conduct, in every circumstance and occurrence of human life.”

**** “If we examine those arguments which, in any of the sciences…are supposed to be the mere effects of reasoning and reflection, they will be found to terminate, at last, in some general principle or conclusion, for which we can assign no reason but observation and experience.”


3 thoughts on “An Enquiry Concerning Human Understanding

  1. That was a pretty spot-on summary of Hume. Oh, and you tweet in elvish. Sorry to break this to you, but a girl who tweets in elvish is pretty much every guy’s dream. Or every smart guy’s dream, which is even better.
    I feel kind of stupid that I read such a long text on Hume and just got fixated on that. You. Tweet. In. Elvish.
    That is awesome.

  2. Sorry for the delay in response. Among other things, I was at the APS March Meeting last week (“the superbowl of physics”, ha!), which might have helped me talk about this had I gone to any of the foundations of quantum mechanics sessions. But those tend to get a little wacky.

    As far as the “no logical reason to believe the principles of physics to be true” thing goes, well, yes! Spot-on, as David said. Physics is an experimental science (“experimental science” should be a redundant phrase), so once you go and measure, say, the (rest) mass of the electron, that’s all there is to it until you can come up with some underlying theory that you can test–which will then, of course, have other postulates that must be experimentally determined and taken as a given. Every QM course starts with some statement like “These are the postulates of quantum mechanics: (1) …” (and may god have mercy on your soul from there). Of course, you have some choices as to what you take as a postulate and what as a derivation, but that’s a detail, I guess. If you were much more clever than me you could probably tie this into Goedel’s incompleteness theorems but I’d be pretty far out of my depth there.

    The most fundamental postulate is that we can, you know, do science at all. Followed by things like experiments being repeatable (across space and time), etc., etc. To quote our Dear Leader (Einstein): “The eternal mystery of the universe is its comprehensibility.” (That’s actually carved on a rock outside the physics building here.)

    Being an experimentalist I’m naturally biased towards the primacy of experiment in physics. I think a theorist would argue (straw man alert) that one of the axioms of our universe is that theory works; i.e., it is possible to look at the existing postulates and derivations and come up with new ones that have a chance of being true, or some such nonsense. The history of physics generally bears this out, I suppose.

    So that’s all a long-winded way of saying that yes, there’s no logical reason science should work, there’s no logical reason logic should work, but it does, and isn’t that exciting! Of course, if we ever found some extreme environment where physics started breaking down, the True Physicist would be not disappointed, but thrilled, and say: “Look everyone! I’ve found New Physics! Someone get me a plane ticket to Stockholm!”

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