His idea that our observations are just in our mind and that we cannot know if objects external to our mind exist or if they exist when we are not looking at them is completely irrational and leads to absurdities. — Ron Cram

So, if you think it's absurd that our observations are just in our minds, where do you think they are?

That there is an observer in all our observations that we need to consider is the major epistemological advance that Hume's philosophy caused. He at least reintroduced the problem of induction.

I think it is obvious that an external world exists. I don't think that Kant's proof or Moore's proof or any other proof has been persuasive so far and so I'm preparing a paper for a philosophy journal on a new proof of the external world.

Hume was not the first to bring up the problem of induction. Due to his view that the external world is not provable, Hume greatly overstates the problem of induction. Can you think of anything Hume wrote that is both original and valuable?

I think it is obvious that an external world exists. I don't think that Kant's proof or Moore's proof or any other proof has been persuasive so far and so I'm preparing a paper for a philosophy journal on a new proof of the external world. — Ron Cram

So it seems obvious, but at the same time eludes strict proof. It seems to me like Hume's scepticism is thereby validated.

Hume was not the first to bring up the problem of induction. Due to his view that the external world is not provable, Hume greatly overstates the problem of induction. Can you think of anything Hume wrote that is both original and valuable? — Ron Cram

It's difficult to vouch for the originality of anything in philosophy. Hume's ideas were original enough to contemporaries to influence later philosophies. His scepticism is valuable to get people to rethink things that seem obvious, particularly people who are new to philosophy, since Hume is relatively easy to read. I also think his realization that certain basic concepts, like causality, can not be gleaned by observation is important.

So it seems obvious, but at the same time eludes strict proof. It seems to me like Hume's scepticism is thereby validated. — Echarmion

Yes, the external world seems obvious to me and is also demonstrable. It is also clear that a great many philosophers have seen the external world as obvious but their "proofs" have failed to be persuasive. I don't see how it could be my fault that they did not present better proofs. Nor do I see their failure to do so as a validation of Hume's skepticism which was irrational from the start.

I also think his realization that certain basic concepts, like causality, can not be gleaned by observation is important. — Echarmion

Yes, you are correct that Hume does make the claim that we cannot observe causation. Again, this is clearly false and I will write a future paper on this. Let me explain briefly. Hume was not a student of natural philosophy. While a student at University of Edinburgh, Hume never completed his degree. The fourth year of study required him to complete a course in natural philosophy, but Hume never did. There is no evidence, for example, that Hume ever read the works of Galileo on motion or Johannes Kepler on mathematical physics or Christiaan Huygens on pendulums. If Hume had read Galileo, Kepler and Huygens, he would have had a better foundation to understand Newton. There is evidence that Hume read Newton but he clearly did not understand him. Hume attacked Newton badly in the Treatise. If Hume had studied natural philosophy, he would never have made the claims he made regarding causation.

Hume's illustration of the billiard ball was particularly ill-advised as Hume knew that Locke had discussed this. Although Locke was not a natural philosopher, Locke understood from Newton that one billiard ball can transfer its force by "impulse." When you see one billiard ball roll up and strike another, you are observing a transfer of kinetic energy. There is no question about this. Hume's argument that we jump to this conclusion because of habit or constant conjunction is clearly false. Take a small child to see his first pool table and the child instantly understands that one pool ball has caused the second ball to move. The child understands it the very first time he sees it. Every pool shark with $20 riding on a game has said "Eight ball in the corner pocket." He knows causation is involved. Without causation such predictions would not be profitable. For better philosophy, Hume should have spent more time playing billiards and less time playing backgammon.

The only ground from which one could question causation in this context is if the person held it was not possible to know that an external world exists. To anyone operating on the view the external world is real, then observation of causation is perfectly straightforward in these simple examples. This is also true of Hume's illustration of the burning match. You can watch the flame consume the match. There is no reasonable doubt one is watching causation here.

Again, is there anyone who can think of anything Hume wrote in Treatise Book 1 that is both original and valuable?

Take a small child to see his first pool table and the child instantly understands that one pool ball has caused the second ball to move. — Ron Cram

This is true. Humans intuitively understand events in the world as being causal. But the fact that we intuitively understand the world to be this way doesn't mean that our understanding is correct. We can observe the pool balls striking each other and then moving as a succession of events. But we can't observe the reason why this happens. So it isn't obvious that the first pool ball caused the second to move, only that the second ball moved after the first one struck it. Personally, I do believe that the first ball caused the second to move, so I'm open to the idea that it could be proved logically. I just don't think it's obvious from a philosophical point of view.

Humans intuitively understand events in the world as being causal. But the fact that we intuitively understand the world to be this way doesn't mean that our understanding is correct. We can observe the pool balls striking each other and then moving as a succession of events. But we can't observe the reason why this happens. — Dusty of Sky

"Humans intuitively understand events to be causal." This is at least partly true. Events are understood to be causal. This may be because of intuition and it may be due to the principle of sufficient reason which I take as a reliable axiom of philosophy.

"But we can't observe the reason why this happens." Yes, we can. When we see a billiard ball moving, we can understand that a moving billiard ball has kinetic energy. When the first ball strikes the second ball, the first ball has less kinetic energy (it may slow or stop) and the second ball begins to roll. The second ball now has the kinetic energy. You can watch the transfer of kinetic energy as it happens. There is no question about this. And it can be confirmed by mathematics.

Did you consider the burning match example?

Yes, we can. When we see a billiard ball moving, we can understand that the billiard ball has kinetic energy. When the first ball strikes the second ball, the first ball has less kinetic energy (it may slow or stop) and the second ball begins to roll. The second ball now has the kinetic energy. You can watch the transfer of kinetic energy as it happens. There is no question about this. And it can be confirmed by mathematics. — Ron Cram

What do you mean when you say we can observe kinetic energy being transferred? We can observe the first ball strike the second ball followed by the second ball moving. But you'd observe the same thing if you were watching an animation of pool balls. We can only observe phenomena, but not the reasons behind phenomena. Reasons are not available to our senses, only to our intellects. So I think proving that one pool ball causes the second to move would require a logical proof and not just an appeal to experience.

But you'd observe the same thing if you were watching an animation of pool balls. We can only observe phenomena, but not the reasons behind phenomena. Reasons are not available to our senses, only to our intellects. — Dusty of Sky

But we are not watching an animation. As long as you accept that the external world is real, there is no difficulty in understanding that a moving billiard ball has kinetic energy.

"Reasons are not available to our senses, only to our intellects." Our senses and our brains work alongside each other constantly. It is not possible to separate the actions of the two. The light flashing on our retinas sends signals to our brains which our brains must interpret. We easily interpret a moving billiard ball as having kinetic energy. This is so easy to do that a child will do it on the child's first exposure to colliding pool balls. Take a three year old to a pool table and ask them what happened when one ball causes another to move and they will tell you plainly that one ball caused the other to move.

What do you mean when you say we can observe kinetic energy being transferred? — Dusty of Sky

I think it is not a master of being able to see energy but of being able to feel it bodily. We feel the resistance, the force and the impact of external objects. We feel the force of the wind. We experience the resistance of the wall; it stops us. We feel the impact of the tennis ball on the racquet, and all the more when it strikes us in the face.

We also feel the energy of our own bodies; our capacity to move things, break things and make things. So it may be true that we don't see causality, but it is false to say we don't experience causality.

As long as you accept that the external world is real, there is no difficulty in understanding that a moving billiard ball has kinetic energy. — Ron Cram

So it may be true that we don't see causality, but it is false to say we don't experience causality. — Janus

Have either of you heard of Malebranche? He believed that the external world was real. However, he also believed that all events in the external world were caused by God. All events in our consciousness, such as feeling the impact of tennis balls, in his view, were also caused by God. God lines up the events in the external world and the events in human consciousness so that they correspond to one another. I think Liebniz believed something similar. How would you prove that they are wrong, that it's the first ball and not God which causes the second ball to move?

How would you prove that they are wrong, that it's the first ball and not God which causes the second ball to move? — Dusty of Sky

Because I don't believe God would deceive us. We can plainly see that one ball has kinetic energy. Kinetic energy is a well-understood, well-described force. For God to be the cause of the second ball moving, God would have to interrupt the action of the moving ball as cause and then insert his own more immediate cause in its place. To do so would be ludicrous, deceptive and unnecessary. Ockham's Razor would say that such an explanation is unnecessary speculation.

I think it is not a master of being able to see energy but of being able to feel it bodily. — Janus

I disagree. We absolutely can see kinetic energy. Anytime you see a falling object, you are looking at kinetic energy. You may not think of that term, but you instinctively know that you do not want to be under a falling boulder because that boulder will hurt you by its kinetic energy.

Also, whenever we look at flame we can see its destructive power. It quickly consumes whatever it is using as fuel. There's no reasonable doubt the flame is causing the fuel to be consumed. You can literally watch it happen.

If anyone knows any Hume followers, please invite them to this thread. If anyone can show me something both good and original in Hume's Treatise Book 1, I will appreciate it!

We don't literally see kinetic energy, we see objects moving and colliding and them moving in different directions. I agree we see flame and burning things being consumed. We also feel the heat of flame.

We don't literally see kinetic energy, — Janus

When you see an object moving, why do you think that you are not seeing kinetic energy?

Because all you are seeing is an object moving. try this: what does kinetic energy look like to you? For example: how large is it? What colour is it? What shape does it have?

what does kinetic energy look like to you? — Janus

Kinetic energy looks like an object moving, such as an object falling or a ball rolling down an incline plane. If you had read of Galileo's experiments or Huygens work on pendulums or the experiments by s'Gravesande, this would be obvious. But even without those experiments, don't you instinctively feel that a falling boulder is dangerous? If you saw a boulder rolling quickly down a hill, wouldn't you want to get out of the way? Of course you would! Ask yourself why! You know the boulder moving quickly has force and energy and would do you great damage.

This is, at least in part, why Galileo studied motion, Huygens studied pendulums and s'Gravesande studied kinetic energy. s'Gravesande would use objects of different weights and drop onto soft clay from different heights. Then he would measure the depth of the impression the object made in the clay as a way to measure the object's kinetic energy. Of course, he wasn't calling it that. The term "kinetic energy" wasn't coined until the 1800s, but that is what he was measuring.

Objects have different types of energy as well. There is potential energy, rest energy and inertial energy. When an object is moving, you are looking at kinetic energy. It is plainly visible and can be mathematically modeled. Kinetic energy can be of any size, any shape and any speed. Kinetic energy doesn't have color because color is a secondary quality.

An object moving does not look like kinetic energy, because if it did you would be able to gauge from the mere appearance the degree of kinetic energy present.

Of course if I saw a boulder rolling down a hill I would get out of the way, but that is not on account of how it appears but of my bodily experience with the impact of heavy objects. The boulder I see rolling down the hill might be made of styrofoam in which case I would be mistaken to think I was in danger.

Kinetic energy can be of any size, any shape and any speed. Kinetic energy doesn't have color because color is a secondary quality. — Ron Cram

And that's the problem with what you are claiming, Things we can see are always of some colour and tone (excluding monochromal objects which are tonal only, and transparent objects). But the latter always reflect their environment to some degree and so still look like they are coloured and tonal.

I am already aware enough of the different categories of energy, so no need to school me on that. If we can see kinetic energy then we ought to be able to see "potential energy, rest energy and inertial energy" (which are really all just potential energy as far as I remember) but we can't. When we see an object at rest we cannot see its potential energy which depends on its mass, which we cannot see. A moving object's kinetic energy also depends on its mass and we can't see that there either.

I have heard of Malebranche and was vaguely aware that his view is similar to Leibniz'. It seems odd to say that God causes, for example, the feeling of impact when we are struck by an object. Sure, this world could be a simulacrum created by God, but to what purpose would he create a simulacrum rather than the real thing? Is God lazy or something? Having said that it might be more effort to create the simulacrum because that would keep him constantly busy, whereas the real thing could be left to unfold causally under its own initial momentum.

I cannot grasp why anyone would think Hume a good philosopher or would claim that he has advanced knowledge. — Ron Cram

I suggest reading An Enquiry Concerning Human Understanding.

Here's a passage on causation.

54. The generality of mankind never find any difficulty in accounting for the more common and familiar operations of nature—such as the descent of heavy bodies, the growth of plants, the generation of animals, or the nourishment of bodies by food: But suppose that, in all these cases, they perceive the very force or energy of the cause, by which it is connected with its effect, and is for ever infallible in its operation. They acquire, by long habit, such a turn of mind, that, upon the appearance of the cause, they immediately expect with assurance its usual attendant, and hardly conceive it possible that any other event could result from it. It is only on the discovery of extraordinary phaenomena, such as earthquakes, pestilence, and prodigies of any kind, that they find themselves at a loss to assign a proper cause, and to explain the manner in which the effect is produced by it. It is usual for men, in such difficulties, to have recourse to some invisible intelligent principle as the immediate cause of that event which surprises them, and which, they think, cannot be accounted for from the common powers of nature. But philosophers, who carry their scrutiny a little farther, immediately perceive that, even in the most familiar events, the energy of the cause is as unintelligible as in the most unusual, and that we only learn by experience the frequent Conjunction of objects, without being ever able to comprehend anything like Connexion between them. — Hume

Here's something on the external world.

118. It seems evident, that men are carried, by a natural instinct or prepossession, to repose faith in their senses; and that, without any reasoning, or even almost before the use of reason, we always suppose an external universe, which depends not on our perception, but would exist, though we and every sensible creature were absent or annihilated. Even the animal creation are governed by a like opinion, and preserve this belief of external objects, in all their thoughts, designs, and actions.

It seems also evident, that, when men follow this blind and powerful instinct of nature, they always suppose the very images, presented by the senses, to be the external objects, and never entertain any suspicion, that the one are nothing but representations of the other. This very table, which we see white, and which we feel hard, is believed to exist, independent of our perception, and to be something external to our mind, which perceives it. Our presence bestows not being on it: our absence does not annihilate it. It preserves its existence uniform and entire, independent of the situation of intelligent beings, who perceive or contemplate it.

But this universal and primary opinion of all men is soon destroyed by the slightest philosophy, which teaches us, that nothing can ever be present to the mind but an image or perception, and that the senses are only the inlets, through which these images are conveyed, without being able to produce any immediate intercourse between the mind and the object. The table, which we see, seems to diminish, as we remove farther from it: but the real table, which exists independent of us, suffers no alteration: it was, therefore, nothing but its image, which was present to the mind. These are the obvious dictates of reason; and no man, who reflects, ever doubted, that the existences, which we consider, when we say, this house and that tree, are nothing but perceptions in the mind, and fleeting copies or representations of other existences, which remain uniform and independent. — Hume

In short, we see the table, but the table isn't in our so-called mind. Its image or representation is.

Here is Hume on skepticism.

There is a species of scepticism, antecedent to all study and philosophy, which is much inculcated by Des Cartes and others, as a sovereign preservative against error and precipitate judgement. It 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. But neither is there any such original principle, which has a prerogative above others, that are self-evident and convincing: or if there were, could we advance a step beyond it, but by the use of those very faculties, of which we are supposed to be already diffident. The Cartesian doubt, therefore, were it ever possible to be attained by any human creature (as it plainly is not) would be entirely incurable; and no reasoning could ever bring us to a state of assurance and conviction upon any subject.

It must, however, be confessed, that this species of scepticism, 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 judgements, and weaning our mind from all those prejudices, which we may have imbibed from education or rash opinion. To begin with clear and self-evident principles, to advance by timorous and sure steps, to review frequently our conclusions, and examine accurately all their consequences; though by these means we shall make both a slow and a short progress in our systems; are the only methods, by which we can ever hope to reach truth, and attain a proper stability and certainty in our determinations. — Hume

I think of Hume as a sensible, serious guy.

But even without those experiments, don't you instinctively feel that a falling boulder is dangerous? If you saw a boulder rolling quickly down a hill, wouldn't you want to get out of the way? Of course you would! Ask yourself why! You know the boulder moving quickly has force and energy and would do you great damage. — Ron Cram

I agree that we would move out of the way. We would be afraid. Call it instinct. A big noisy thing coming at us scares us out of its path. But how does this apply to the Hume I know? I take it as a given that we act on perceived regularities in experience. We expect them to continue, without being able to justify it deductively. To me that's the fascinating part. 'Pure' reason is mostly impotent. Science has an 'irrational' (non-deductive) ground. This chair will continue to hold me, I think, because it has so far. If I look for the logic in that, it leaps away from me --though the temptation is a circular argument that assumes the very uniformity of nature that it wants to prove. 'The future will resemble the past, because in the past the future resembled the past. ' To see that there is no argument for this instinctual expectation is not to quench this expectation (which is impossible.) Instead it leaves a central faculty of the mind mysterious to that same mind.

Anyway, one more passage on Hume's sensible skepticism.

But a Pyrrhonian cannot expect, that his philosophy will have any constant influence on the mind: or if it had, that its influence would be beneficial to society. On the contrary, he must acknowledge, if he will acknowledge anything, that all human life must perish, were his principles universally and steadily to prevail. All discourse, all action would immediately cease; and men remain in a total lethargy, till the necessities of nature, unsatisfied, put an end to their miserable existence. It is true; so fatal an event is very little to be dreaded. Nature is always too strong for principle. And though a Pyrrhonian may throw himself or others into a momentary amazement and confusion by his profound reasonings; the first and most trivial event in life will put to flight all his doubts and scruples, and leave him the same, in every point of action and speculation, with the philosophers of every other sect, or with those who never concerned themselves in any philosophical researches. When he awakes from his dream, he will be the first to join in the laugh against himself, and to confess, that all his objections are mere amusement, and can have no other tendency than to show the whimsical condition of mankind, who must act and reason and believe; though they are not able, by their most diligent enquiry, to satisfy themselves concerning the foundation of these operations, or to remove the objections, which may be raised against them.
...
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. The greater part of mankind are naturally apt to be affirmative and dogmatical in their opinions; and while they see objects only on one side, and have no idea of any counterpoising argument, they throw themselves precipitately into the principles, to which they are inclined; nor have they any indulgence for those who entertain opposite sentiments. To hesitate or balance perplexes their understanding, checks their passion, and suspends their action. They are, therefore, impatient till they escape from a state, which to them is so uneasy: and they think, that they could never remove themselves far enough from it, by the violence of their affirmations and obstinacy of their belief. But could such dogmatical reasoners become sensible of the strange infirmities of human understanding, even in its most perfect state, and when most accurate and cautious in its determinations; such a reflection would naturally inspire them with more modesty and reserve, and diminish their fond opinion of themselves, and their prejudice against antagonists. The illiterate may reflect on the disposition of the learned, who, amidst all the advantages of study and reflection, are commonly still diffident in their determinations: and if any of the learned be inclined, from their natural temper, to haughtiness and obstinacy, a small tincture of Pyrrhonism might abate their pride, by showing them, that the few advantages, which they may have attained over their fellows, are but inconsiderable, if compared with the universal perplexity and confusion, which is inherent in human nature. In general, there is a degree of doubt, and caution, and modesty, which, in all kinds of scrutiny and decision, ought for ever to accompany a just reasoner. — Hume

An object moving does not look like kinetic energy, because if it did you would be able to gauge from the mere appearance the degree of kinetic energy present. — Janus

But you can! Kinetic energy is motion. To measure or estimate the kinetic energy, you multiply mass times velocity. At the same speed, the larger the object the greater the kinetic energy. Also, at the same mass, the faster it's moving the greater the kinetic energy.

Let's take for example, a thrown baseball. You can see that a 45 mph pitch is not moving as fast as a 95 mph pitch. And you intuitively know that the 95 mph pitch has more kinetic energy and would hurt far more than a 45 mph pitch.

In the same way, if a car bumps into you at 0.5 mph, it won't hurt much. But if a car hits you at 35 mph it will probably kill you. You can literally see the kinetic energy is much greater and much more dangerous at 35 mph.

Now let's look at the kinetic energy in hurricane force winds. The air molecules (nitrogen, oxygen, argon, carbon dioxide, etc.) being blown about are so small you cannot see them. Because there are so many small molecules you calculate the kinetic energy differently and it's much more complicated. See https://planetcalc.com/4773/

We have to use instruments for some of the inputs for that calculation. However, you can see trees blowing about as an effect of the wind and you can estimate the speed of the wind from its effects. To your point, we can also feel the power of the wind. To my point, we can observe its effects and estimate its speed and we can use instruments to study the kinetic energy of wind more precisely.

I am already aware enough of the different categories of energy, so no need to school me on that. If we can see kinetic energy then we ought to be able to see "potential energy, rest energy and inertial energy" (which are really all just potential energy as far as I remember) but we can't. When we see an object at rest we cannot see its potential energy which depends on its mass, which we cannot see. A moving object's kinetic energy also depends on its mass and we can't see that there either. — Janus

No, potential energy, mass rest energy and inertial energy are not the same. And yes, we can see them all if we know what we are looking at. I won't bore with a full report, but let's look at rest mass energy for a moment. We learned from Einstein that matter is convertible into energy and energy into matter. That's what his famous equation E=mc^2 was all about. You can easily compare the rest mass energy of one small object to the rest mass energy of another small object. Rest mass energy also contains the kinetic energy, so if one of them is moving - that complicates things.

Hume admitted in the Treatise that he did not understand motion. When he discusses motion, he talks about "unknown causes." The causes are not unknown to the natural philosophers of his day, only to Hume because he didn't complete his degree.

I think of Hume as a sensible, serious guy. — joshua

I have read Hume's first Enquiry. Have you read his Treatise?

Hume says that his philosophy is the same in both books, I believe this to be mainly accurate although there are a few changes. In addition, the Treatise is much more specific about why he holds the views he does. The Treatise is also much more honest about the absurdities his philosophy creates. Hume goes into great deal about this in Treatise 1 iv 7. Have you read it?

Sometimes Hume struggles to maintain his idea that external objects do not have a real or continued existence when not being observed:

I am here seated in my chamber with my face to the fire; and all the objects, that strike my senses, are contained in a few yards around me. My memory, indeed, informs me of the existence of many objects; but then this information extends not beyond their past experience, nor do either my senses or memory give any testimony to the continuance of their being. When therefore I am thus seated, and revolve over these thoughts, I hear on a sudden a noise as of a door turning upon its hinges; and a little after see a porter, who advances toward me. This gives occasion to many new reflections in reasonings. First, I never have observed, that this noise could proceed from anything but the motion of a door; and therefore conclude, that the present phenomenon is a contradiction to all past experience, unless the door, which I remember on the other side of the chamber, be still in being. Again I have always found, that a human body was possessed of a quality, which I call gravity, and which hinders it from mounting in the air, as this porter must have done to arrive at my chamber, unless the stairs I remember be not annihilated by my absence. But this is not all. I receive a letter, which upon opening it I perceive by the handwriting and subscription to have come from a friend, who says he is two hundred leagues distant. It is evident I can never account for this phenomenon, conformable to my experience in other instances, without spreading out my mind the whole sea and continent between us, and supposing the effects and continued existence of posts and ferries, according to my memory and observation. To consider these phenomena of the porter and letter in a certain light, they are contradictions to common experience, and may be regarded and may be considered objections to these maxims, which we form concerning the connections of causes and effects. I am accustomed to hear such a sound, and see such an object in motion at the same time. I have not received in this particular instance both these perceptions. These observations are contrary, unless I suppose that the door still remains, and that it was opened without my perceiving it: And this supposition, which was at first entirely arbitrary and hypothetical, acquires a force and evidence by its being the only one, upon which I can reconcile these contradictions…. Here then I am naturally led to regard the world, as something real and durable, and as preserving its existence, even when it is no longer present to my perception. Location 2910, 32%, Treatise 1.4.2

For most people, Hume’s experience would be adequate to persuade then that a world of objects external to their mind really exists. But Hume has embraced this idea that sense data cannot convey the existence of objects external to the mind and so he’s in a quandary. For those among us who are convinced of the external existence of objects, it is easy to believe in their continued existence when not being sensed. Hume’s idea that the stairs should be annihilated by his absence seems absolutely bizarre to us, but follows, if uncomfortably, for those who are not convinced in the existence of external objects.

Hume continues his “reasonings”:
But whatever force we may ascribe to this principle, I am afraid it is too weak to support alone so vast an edifice, as is that of the continued existence of all external bodies; and that we must join the constancy of their appearance to the coherence, in order to give a satisfactory account of that opinion. As the explication of this will lead me into a considerable compass a very profound reasoning; I think it proper, in order to avoid confusion, to give a short sketch or abridgement of my system, and afterwards draw out all its parts in their full compass. This inference from the constancy of our perceptions, like the precedent from their coherence, gives rise to the opinion of the continued existence of body, which is prior to that of its distinct existence, and produces that latter principal. Location 2943, 32% Hume, Treatise, 1.4.2

And so despite the logical need for stairs to exist for the porter to climb, in spite of the logical need for his friend to continue to exist in order to write him a letter, in spite of his friend’s statement of being 200 leagues distant - even so, Hume cannot find a reason to believe in the continued existence of an external world. Hume loves sceptical thoughts too much to let them go.

In his Abstract, which Hume wrote to increase sales of his Treatise, Hume writes about himself and his philosophy in the third person. Paragraph 28 reads:

By all that has been said the reader will easily perceive that the philosophy contained in this book is very sceptical, and tends to give us a notion of the imperfections and narrow limits of human understanding. Almost all reasoning is there reduced to experience; and the belief, which attends experience, is explained to be nothing but a peculiar sentiment, or lively conception produced by habit. Nor is this all; when we believe anything of external existence, or suppose an object to exist a moment after it is no longer perceived, this belief is nothing but a sentiment of the same kind. Our author insists upon several other sceptical topics; and upon the whole concludes that we assent to our faculties, and employ our reason, only because we cannot help it. Philosophy would render us entirely Pyrrhonian, were not nature too strong for it. (Abstract, Para 28)
http://web.mnstate.edu/gracyk/courses/web%20publishing/hume'sabstract.htm

This is a telling paragraph. While Hume began with doctrines designed to support full Pyrrhonian scepticism, when he arrived at his destination he found it unlivable. Hume reports that “nature is too strong for it.” This is an interesting phrase. If an external world cannot be known, what is this 'nature' Hume refers to?

Later Hume will attempt that to make his philosophy livable one must adopt an unprincipled "on-again, off-again" scepticism. This is what you call "sensible scepticism." His attempt doesn’t really work, because it is inconsistent and Hume retains the doctrines that lead to full scepticism.

Changes in Hume’s philosophy between his A Treatise of Human Nature (THN) and An Enquiry Concerning Human Understanding (EHU) have been noted by others. One change was that Hume was unhappy with his reasonings on personal identity in THN and so he does not address the subject in EHU. The present point is that the beginning of EHU contains little hint that Hume doubts the existence of an external world. However in Section 119 of EHU, Hume shows that he still holds this view:

119. By what argument can it be proved, that the perceptions of the mind must be caused by external objects, entirely different from them, though resembling them (if that be possible) and could not arise either from the energy of the mind itself, or from the suggestion of some invisible and unknown spirit, or from some other cause still more unknown to us? It is acknowledged, that, in fact, many of these perceptions arise not from anything external, as in dreams, madness, and other diseases. And nothing can be more inexplicable than the manner, in which body should so operate upon mind as ever to convey an image of itself to a substance, supposed of so different, and even contrary a nature.

It is a question of fact, whether the perceptions of the senses be produced by external objects, resembling them: how shall this question be determined? By experience surely; as all other questions of a like nature. But here experience is, and must be entirely silent. The mind has never anything present to it but the perceptions, and cannot possibly reach any experience of their connexion with objects. The supposition of such a connexion is, therefore, without any foundation in reasoning.

Clearly, Hume denies the possibility of knowing if objects external to the mind actually exist or not. Interestingly, Hume does not discuss in EHU the difficulties such a view visits on daily life, as he did on THN.

Hume's "sensible scepticism" is really just an admission that his philosophy is irrational and unlivable.

Hume's "sensible scepticism" is really just an admission that his philosophy is irrational and unlivable. — Ron Cram

One might be overlooking contexts. Hume’s Treatise was in many a way a reply to both Descartes and Berkeley. Understand the logic used by these two predecessors and one might, maybe, hold a more empathetic view of Hume’s logic, for it serves to counteract the effects of Cartesian skepticism and that of Berkeley’s subjective idealism. This by illustrating how all our knowledge is built out of habituated thoughts inductively put together – thereby impelling one to reappraise the logic used by both Descartes and Berkeley. But I get it; Hume’s not to your liking. To each their own. And no, I've no interest in composing a thesis to support the just mentioned perspective.

As to what is both original and good in Book 1 of the Treatise, good to whom? This possible trick question has some degree of importance to it.

Hume’s detailed musings on what would nowadays be most properly termed experientialism (and not empiricism) and of what he termed probabilistic reasoning (due to the possibility of error – which is nothing else but the pragmatist notion of fallibilism) are original in the details they present, but I take it you don’t deem them to be good. So be it.

On the other hand, bundle theory (which you’ve alluded to) was originated in the western world via book 1 of the Treatise – Hume’s noted dissatisfaction with it at the end of the treatise aside. This theory has persisted as an important ontological hypothesis since. So it is both original to at least western thought and good to a large number of individuals.

But again, by what standards do you demarcate the goodness of ideas?

But again, by what standards do you demarcate the goodness of ideas? — javra

This is a good and fair question. In general terms, the goodness of ideas is found in their truthfulness and their benefit. Truth is that which is in accord with reality. Reality, in the words of the great philosopher Dallas Willard, is "what you run into when you are wrong." Running into reality can be painful. By knowing more of the truth, then you will experience less pain - which we can all agree is a benefit.

More specifically, in terms of philosophy, I'm wondering what in Hume's Treatise Book 1 has shown itself to be true and beneficial? Hume's claim that we cannot know that external objects exist is irrational (and disproven in the paper I'm preparing). Hume's idea that causation cannot be observed is counter to our everyday experience and completely irrational. Hume's attack on induction is original but vastly overstated.

Perhaps you are wondering if any philosopher has ever lived up to the lofty standards I am expecting of Hume. Yes! For example, Aristotle's physics are terrible. He was wrong about many things. But he is also the author of deductive logic. It is not that Aristotle was the first to use deductive logic, but he was the first to write down the rules. Of course, the rules have been clarified and enlarged over the centuries and new forms of logic have arisen. But Aristotle's work here is both original and good. Aristotle has added to our store of philosophical knowledge. Hume has not.

No, potential energy, mass rest energy and inertial energy are not the same. — Ron Cram

Can you explain the difference between them?

I still don't think it is reasonable to say that we can see energy, nothing you have said convinces that it is, so we'll just have to agree to disagree about that.

Rather than get lost in details, I'll try to focus the issue. I don't think Hume doubted the existence of the external world. His 'ruling passion' was a love of literary fame. If you read his own brief description of his life (written as it was ending), you'll see that he was a man of the world.

https://davidhume.org/texts/mol/

Philosophy would render us entirely Pyrrhonian, were not nature too strong for it. — Hume

I think one ought to read this line anti-metaphysically and even anti-philosophically if philosophy is understood in its abstruse and ridiculous aspect. Nature is indeed too strong for our merely theoretical doubts. When such doubts aren't just toys for the exhibition of cleverness and creativity, they are perhaps useful against positive metaphysical assertions (theological confusions, etc.)

The idea that one should bother with a proof of the external world strikes me as absurd. Only a person in the grip of madness doubts the external world, and they might as well doubt the legitimacy of a complicated 'proof' of this world as well. So I think we agree that doubting the external world is just ridiculous. But I think we disagree on what kind of chap Hume was.

Nature being to strong means Hume,in the terms you are using, thinks there are external objects.

We are affected by nature in certain ways. Things happen to us, all around us, within are experiences. The sceptic is destined to fall to what appears in our impressions. From beginning to end, someone can whine they don't have "proof" a billiard ball is about it hit them in the face, but then it does. Nature is too strong for our wish for "proof" to matter.

From here, we can actually extend scepticism to a proof of external objects. The motivation of the sceptic is entirely driven by the existence of external objects. What is the monster we fear so much as a sceptic? Making a mistake, taking an unjustified/untrue position, the world being other to what appears own our experiences.

To participate in any sceptical project is a tact acceptance of the externality of objects. If there were no external objects there couldn't be a mismatch between what appears to us and what was true. Scepticism would be incoherent. It needs a world which can be other to our experience.

A world other than our experiences also has implications for how a scepticism can conceivably function. It must turn not only on certain assertions of what is true (as they might be wrong), but also on any sceptical rejection of a claim (as a claim might also be true). The coherent sceptic must, like Hume, oscillate between scepticism of one claim and accepting it (i.e. scepticism of rejecting it).

Hume isn't laying out a rejection of external objects, knowledge or philosophy. He's analysing the relationship of our reason to knowledge, trying to break with a philosophy which holds our reason or concepts are how our knowledge obtains (as in poor surface readings of Descartes and Berkeley).

We might say Hume is trying to recognise the life of the external world, that it is the things outside us which determine their existence, rather than us having an experience or concept. In this metaphysical space, he is constantly sceptical because he recognises our concepts are distinct from how something is true/made true.

Can you explain the difference between them? — Janus

Yes. Potential energy is the energy an object holds relative to other objects. Think of a boulder perched on the side of a cliff above a highway. Someone or something, perhaps gravity, dislodges the boulder so that it begins rolling down the hillside. Once it begins rolling, you are looking at kinetic energy. Before it begins rolling, you are looking at potential energy. Another way to conceive of potential energy is the store of energy necessary to put the boulder back in its original position above the highway. To put the boulder back would require you to expend energy. The energy you expend in that effort is now the potential energy stored in the boulder once it is back in place.

Mass rest energy I explained last time. To repeat, Einstein came up with the equation E=mc^2. This equation explains conversion of energy to matter and matter to energy. Matter to energy is easy to explain by thinking of a fire in the firepit. The wood, coal or natural gas in the firepit is the matter. By burning it, you turn matter into heat energy. That's one example.

Inertial energy is the energy an object has at rest. This may seem confusing because it sounds similar to mass rest energy, because relates to objects at rest. But only the names are similar. Inertial energy doesn't have to do with conversion but to motion. The more massive the object, the greater its inertial energy. The shape of the object also contributes to its inertial energy. One billiard ball can easily move another billiard ball because the second billiard is round, it rolls easily and is the same size as the first billiard ball. But if you put a much bigger, flat boulder on the billiard table, the billiard ball would not be able to move it even when moving quickly. The boulder has a lot more inertial energy than the ball.

Newton described vis inertia in his Principia but this is one of the issues Hume never understood. Motion, power, energy, inertia were all mysteries to him. But lack of facts never stopped Hume from pontificating from his position of suspension of judgment.

The idea that one should bother with a proof of the external world strikes me as absurd. Only a person in the grip of madness doubts the external world, and they might as well doubt the legitimacy of a complicated 'proof' of this world as well. So I think we agree that doubting the external world is just ridiculous. — joshua

If your only exposure to Hume is his Enquiry Concerning Human Understanding, I can see why you might think that. Hume does not even hint at his doubt of the external world in the early part of the book (but read section 119 closely). However, in his Treatise Book 1, Hume is highly skeptical and he is very upfront about it. He was much influenced by Pyrrhonism.

The goal of Pyrrhonism is the “suspension of judgement” resulting in a lack of knowledge or belief about everything, including what things absolutely and really exist. By suspending judgement, Pyrrhonists believe they will achieve a state of happiness marked by freedom from distress and worry. Pyrrhonism was distilled into the “ten modes of Aenesidemus” or the “five modes of Agrippa.” Hume has developed his own series of doctrines which have the same goal as Aenesidemus and Agrippa, suspension of judgement. Hume describes and attempts to support these doctrines in the first part of the Treatise Book 1.

Kant read Hume and was "awakened" from his "dogmatic slumbers." Kant said it was a scandal that philosophy had never offered a solid proof of an external world and he then described a proof that he claimed was the only possible proof. People found it wanting. Others have tried and their efforts have also been found wanting. You can read Moore's famous proof here. http://joelvelasco.net/teaching/4330/moore-onskepticism.pdf

You are correct that most people, even most philosophers accept the reality of objects external to their minds. But there is a significant minority of Hume followers who do not accept that it is proven, even though they may agree it is probable. Hume followers do not have much faith in probability.

If you want to know more about Hume and his view of the external world, you can read Hume in Treatise Book 1 or you can read the book by HH Price.
https://www.amazon.com/Humes-Theory-External-Habberley-1940-12-06/dp/B01HC14VU4/