David Hume

(1711-1776)

Home: Edinburgh, Scotland

School: Associationism. This was a philosophical school that recognized the limitations of sensory information. Learning was seen as beginning through the intake of error-riddled sensory information concerning "objective reality" and formed through repeated pairings of rewards/punishments tied to behaviors. While this is a thorougly behavioristic understanding of learning, Hume was also an Irrationalist in that he felt that it was emotions shaped human consciousness, not reason or logic - and even more than this, it was emotional preference that shaped the "oughts" of ethical and moral systems. Despite this view, or perhaps because of it, David Hume was a precursor to radical behaviorism - he held a hedonistic viewpoint towards motivation, built on reward and punishment, rejected the idea of the "Self" and maintained a positivistic viewpoint towards empirical and demonstrative data.

Rational/Empirical: Empiricist/Skeptic/Positivist. Don't mistake Hume's "Irrationalist stance" to mean that he himself valued being irrational - he was just acknowleding that human emotion was a motivator to thought and action. He was amongst the great empirical and scientific thinkers of all time. Hume created a Newtonian model for social science.

Greatest Achievement: One of the first purely modern views towards consciousness

Religious viewpoint: Skeptic.

Significant Works: A Treatise of Human Nature (3 vol., 1739-40) and An Enquiry Concerning the Human Understanding (which is covered in detail below.)

I am very happy to submit this new entry on David Hume. It now includes a detailed analysis of his work "An Enquiry Concerning the Human Understanding." (I also include key points from the useful, albeit contentiously written "Hume's Abject Failure" by John Earman.)

What follows first are some important quotes from his writings that capture the essence of the man:

"I am an American."
Mr. Hume never even visited America, let alone became a citizen, but with this statement he came out in favor of American ideals of liberty, self-determination and freedom of thought at a time when America most needed it. Bravo!

"Nothing is sacred or fixed"
Here we see Hume's argument against certain, objective knowledge - and in doing so he comes off as a seemingly prescient thinker, particularly in relation to. Einstein's theory of relativity.

"When men are most sure and arrogant, they are commonly the most mistaken. (Dogmatism)"
Surely no comment needed. Ironically one of Hume's most famous works may suffer from this arrogance.

"The Christian religion not only was at first attended with miracles, but even at this day cannot be believed by any reasonable person without one."
This represents Hume's view of "revelation". ==Custom, then, is the great guide of human life. An Enquiry Concerning Human Understanding, sct. 5, pt. 1 (1748). == This statement embodied Hume's belief in political obedience arising from habit, as opposed to consent through a "social contract.", or through obediance to God. We comply to rules because the very existence of rules. With rules come rewards and punishments and these concomitant rewards and punishments shape what we then come to believe are correct behaviors. =="Avarice, the spur of industry." Essays Moral, Political, and Literary, "Of Civil Liberty" (1742). == This reveals Hume's belief that it was a simple hedonistic drive, and not a desire for public welfare, that led to the foundations of states and society. Again, this is most certainly correct. See my entry on Ayn Rand who states that this "selfishness" is not only not immoral, but the only moral manner of motivation.

A brief review of Hume's philosophy as it pertains to psychology:
David Hume agreed with George Berkeley that we could never experience the physical world directly - we only have our central nervous system's limited and flawed perceptions of it. Hume wrote: "The mind has never any thing present to it but the perceptions and cannot possibly reach any experience of their connexion (sic) with objects." Hume distinguished between impressions that were strong, and ideas, which were just fading perceptions - he therefore, in opposition to Plato and Descartes, held that sensory perceptions were the most certain of our experiences, not the least.

To Hume, all simple ideas were once impressions. Once in the mind, they could be rearranged by the imagination into complex ideas, which explained why we could imagine "new" concepts that we had never actually perceived. Hume wrote: "... all our simple ideas in their first appearance, are derived from simple impressions, which are correspondent to them, and which they exactly represent". These views follow the tenets of Realism and Reductionism.

Did Hume Deny that the real world existed?
Like Berkeley, Hume did not deny the existence of physical reality, he denied the possibility of knowing 'it' directly - Kant's 'Thing in itself'. Hume and Berkeley both differentiated between reason and sensation. Hume, however, went further, endeavoring to prove that reason and rational judgments are merely habitual associations of distinct sensations or experiences.

Hume's Fork
Hume's Fork is a method of delineating two different forms of knowledge. Hume made a distinction between two forms of empirical knowledge: analytical experience and synthetic experience. Analytical experience dealt with concepts or ideas that we hold to be true because their contradiction is necessarily false, they are equivalences, symbols, logical arguments or mathematical equations. With analytical statements we have the certainty of truth at the cost of learning anything new - they provide us with NO information about the outside world, they merely are ways of restating what we know.

Synthetic statements are a posteriori in nature, they deal with facts, and we make them after we observe them with the senses. They provide us with information, but at the cost of metaphysical certainty.

Hume says that we should ask the following about any philosophical proposition:

Does it contain matters of fact? Is so, point to your evidence.

Does it offer a relationship of ideas? If so, provide your logical argument

If neither, then the statement is literally meaningless.

I'll return to Hume's fork after I write on his views of causality.

Hume and Causality
Hume's view of causality is controverisal. Like other empiricists, Hume believed the contents of the mind came only from experience. His "Association of Ideas" theory explained the similarity of ideas between all men: Resemblance and contiguity were the general guiding forms of all ideas. ('Contiguity' is Aristotle's idea that the learning of cause and effect relationships comes by seeing the 'cause' and the 'effect' paired at the same time/place)

Hume's causality was therefore a psychological phenomena, discoverable only through experience, and not reason. According to Hume's Fork, knowledge of matters of fact through reason is impossible! We cannot justify causality logically, because it's denial is not a logical contradiction. And we cannot prove causality from experience, because we cannot observe every event. While our minds reason in terms of cause and effect, we have no such actual knowledge empirically that this is the case. Yes, we observe Y following X, but we cannot observe that Y follows x in EVERY case. It's a very good assumption, even an axiom, but it's not a metaphysical certainity. There may well be effects without causes, or effects that proceed causes. We can't rule out such things a priori.

Hume used the same types of argument againgst the theistic contention that we could be sure that god created the universe. Hume stated that we could not be sure of causal connections in ANYTHING, even those things we have observed, let alone with the creation of universes, of which we had no experience whatsoever.

As a practical matter he freely acknowledged that people had to think in terms of cause and effect, and had to assume the validity of their perceptions, or they would go mad (See Vaihinger's philosophy of "As If"). So why did Hume bother in the first place? Because he felt it important to make the distinction between claiming that something must be the case and saying that, in practice, we have always found it to be the case. Causality is a habit of the imagination, based on past observation, not an undeniable objective rule of nature. Hume worked out how this process functions for us:

Hume's laws of Cause and effect:
1) The cause and effect must be contiguous (together) in the same space/time

2) The cause must be prior in time to the effect

(This goes against the "Big Crunch" cosmological theory)

3) There must be a constant union between the two

(This goes against magical means of creation)

4) The same cause must always produce the same effect, and vice versa.

By showing that causal connections are not an a priori constuct of the mind, nor a metaphysical reality of the universe, one might say that Hume paved the way for quantum theory.

Hume also attacked the concept of a soul. Hume's skeptical approach denied the existence of the spiritual substance postulated by Berkeley and the "material substance" of Locke. Dissatisfied with merely obliterating the outer universe, Hume denied the existence of the individual self with a brilliant observation that maintained that because people do not have a constant perception of themselves as distinct entities, they:


 * "...are nothing but a bundle or collection of different perceptions... The mind is no more than the perceptions we are having at any given moment. When I enter most intimately in what I call myself...I never can catch myself at any time without a perception, and never can observe anything but the perception. When my perceptions are removed for any time, I am insensible of myself...And were my perceptions removed by death... I should be entirely annihilated."

Finally, Hume found that emotions, unchanged for centuries, could account for the driving motivation for all men. His opinion was that the passions associated with ideas, not rationalism, ruled the mind. This theory known as Irrationalism, was a prelude to Freud, who felt that the concept of irrationalism as our true motivator in life represented a grand discovery. It's certainly still news to many people today.

Now, I would like to present:

An Enquiry Concerning The Human Understanding
Basic Assumptions of the Enquiry:


 * Empiricism: Ideas (or concepts) are entirely sense-impression based.


 * Psychologism: theory of knowledge should describe the operations of the mind by which knowledge is (or isn't) produced.

Hume begins the Enquiry by first showing that certainties such as our view of our selves as a "constant" being through time is an illusion:


 * It must be some one impression that gives rise to every real idea. But self or person is not any one impression, but that to which our several impressions and ideas are supposed to have a reference. If any impression gives rise to the idea of self, that impression must continue invariably the same, through the whole course of our lives; since self is supposed to exist after that manner. But there is no impression constant and invariable. Pain and pleasure, grief and joy, passions and sensations succeed each other, and never all exist at the same time. It cannot therefore be from any of these impressions, or from any other, that the idea of self is derived; and consequently there is no such idea. (Treatise I:4:vi)

Here, Hume attacks our very sense of the certainty of our senses by showing that we can't even be certain that the thing we call "self" exists as a continuous being, and in doing so he carries Locke's empiricism to it's inevitable skeptical conclusion:

Locke in talking about matter states that it is "something I know not what"

Berkely states that there is no matter independent of the mind.

Hume does him one better to deny that there is a mind!


 * For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception. When my perceptions are removed for any time, as by sound sleep, so long am I insensible of myself, and may truly be said not to exist. And were all my perceptions removed by death, and could I neither think, nor feel, nor see, nor love, nor hate, after the dissolution of my body, I should be entirely annihilated, nor do I conceive what is further requisite to make me a perfect nonentity. If any one, upon serious and unprejudiced reflection, thinks he has a different notion of himself, I must confess I can reason no longer with him. All I can allow him is, that he may be in the right as well as I, and that we are essentially different in this particular. He may, perhaps, perceive something simple and continued, which he calls himself; though I am certain there is no such principle in me. (Treatise I:4:vi )

and


 * [Selves are] nothing but a bundle or collection of different perceptions which succeed each other with an incomparable rapidity, and are in a perpetual flux and motion. Our eyes cannot turn in their sockets without varying our perceptions. (Treatise I:4:vi)

Now that Hume has shown that the very idea of object constancy of the human self is false, he proceeds to show that our view of causation is not a metaphysical certainty:

Regarding Hume's skeptical view of Causation
The mind is a kind of theatre, where several perceptions successively make their appearance; pass, repass, glide away, and mingle in an infinite variety of postures and situations. (Treatise I:4:v)

Hume states that the idea of necessary connection is entirely empirically baseless, hence the rational basis of induction (probable inference)is called into doubt

The comparison of the theatre must not mislead us. They are the successive perceptions only, that constitute the mind; nor have we the most distant notion of the place there these scenes are represented, or of the materials of which it is composed. (Treatise I:4:vi )

There is good news for free will supporters here, however. Hume sees the (dis)solution of the "free will" problem: free will & determinism are compatible. Free will is a rational concept, stemming from the reasoning of the mind, and determinism stems from observations of the world. This leads us to Hume's Fork:

Hume's Fork Part II
(c.f., Leibniz, Locke) states that knowledge is either of matters of fact: synthetic informative taken from observation or of relations between ideas: analytic and factually uninformative (tautological)

It is remarkable concerning the operations of the mind, that, though most intimately present to us, yet, whenever they become the object of reflexion, they seem involved in obscurity; nor can the eye readily find those lines and boundaries, which discriminate and distinguish them. (Enquiry I)

Regarding Ethics
Next, Hume moves on to ethics. Hume's Ethical Law states that: An "is" cannot entail an "ought". By this he means that morality is a matter of "Sentiment or mental Taste. It cannot be an absolute any more than a food preference can be an absolute." He writes:

[Morality] is entirely relative to the Sentiment or mental Taste of each particular Being; in the same Manner as the Distinctions of sweet and bitter, hot and cold, arise from the particular feeling of each Sense or Organ. (Enquiry I )

This is a particularly enlightening passage, because critics would be quick to cite that we certainly cannot change what appears to us to be "hot" or "sweet", so Hume must be wrong. For this reason, it would seem that morals are in fact universal and unchanging. Yet this line of thought makes the error of tacitly maintaining that such things can be objectively 'hot' or 'sweet' to all beings at all times. We cannot know this, let alone prove this! Again, our views of 'hot' or 'sweet' or even 'moral' are preferences based upon the sort of creatures we are. To mistake this preference for an objective fact is to fail to appreciate that our preferences are not universal!

Regarding Religion
Hume stated that reports of miracles can never rationally warrant belief, because incredible claims require incredible evidence to support them, and verbal reports cannot serve as incredible evidence. This is because an incredible claim, such as a miracle, requires us to invalidate theories of the world that are based upon a multitude of observations over eons of time. In order to overthrow such a massive body of evidence, one must provide more than anonymous 'testimony'. (Testimony cannot actually be anonymous, hence the quotes...)

Against Paley's Watch in the Desert Argument
Hume states that the Argument from Design is unsound because it commits a fallacy of false analogy. We have no experience observing universes being created, and ex nihilo creation is not the same thing as the colloquial usage of the word 'create', as in creating watches from pre-existent parts. Therefore we cannot rely on what we 'know' of 'creation' to soundly state how the universe was created. To build an argument from design from making a comparison to an object like a watch, that we know to be designed, merely assumes what it seeks to prove, and therefore, proves nothing. Paley's argument is nothing more than an emotional appeal.

Ideas & Impressions

 * Impresssions are "our more lively pereceptions, when we hear, or see, or feel, or love, or hate, or desire, or will" (Enquiry II )

Ideas are "less lively perceptions, or which we are conscious, when we reflect on" impressions.


 * [A]ll our ideas or more feeble perceptions are copies of our impressions or more lively ones. (Enquiry II)

Hume's Empiricism is the concept that all ideas arise from impressions directly, by reflection (cf. Locke's "simple ideas"), indirectly by concatenation: e.g. "Golden Mountain" or "God". (Possible exception: shades of color intermediate between two we have experienced might be imaginable without our ever having experienced exactly that color before. )


 * [A]ll this creative power of the mind amounts to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience. When we think of a golden mountain, we only join two consistent ideas, gold, and mountain, with which we were formerly acquainted. (Enquiry II)

And


 * The idea of God, as meaning an infinitely intelligent, wise, and good Being, arises from reflecting on the operations of our own mind, and augmenting, without limit, those qualities of goodness and wisdom. (Enquiry II)

Hume may also be implying that God is not only a creation of the mind through extrapolation, but representative of the mind creating it.

Empiricist Criterion of Meaning - Words without attached ideas are meaningless - there is no idea without constituent impressions:


 * [A]ll our ideas or more feeble perceptions are copies of our impressions or more lively ones. (EnquiryII)

And


 * When we entertain ... suspicion that a philosophical term is employed without any meaning or idea ... we need but enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will ... confirm our suspicion. (Enquiry II)

III: Of the Association of Ideas
Hume begins this section by speaking on the Principle of Association

It is evident that there is a principle of connexion between the different thoughts or ideas of the mind, and that in their appear-ance to the memory or imagination, they introduce each other with a certain degree of method and regularity. (Enquiry II)

Hume sees evidence of Association found in trains of discourse or logical thought and he sees it as almost inescapable. There is coherence even in "our wildest . . . reveries": even these run "not altogether at adventures"

He also points to to commonalities in language as support for his point.

Among different languages, even where we cannot suspect the least connexion or communication, it is found, that the words, expressive of ideas, the most compounded, do yet nearly correspond to each other: a certain proof that the simple ideas, comprehended in the compound ones, were bound together by some universal principle, which had an equal influence on all mankind. (Enquiry III) Hume finally underlines the Three Principles of Connection

To me, there appear to be only three principles of connexion among ideas, namely, Resemblance,Contiguity in time or place, and Cause or Effect. (Enquiry III )

Resemblence: "a picture naturally leads our thought to the original" Enquiry III)

Contiguity: "mention of one apartment naturally introduces and enquiry or discourse concerning the others" (Enquiry III)

And

Cause or Effect: "if we think of a wound, we can scarcely forbear reflecting on the pain" (Enquiry III)

IV: Skeptical Doubts Concerning the Operations of the Understanding
Here we can make use of Hume's Fork again: Knowledge concerns either relations of ideas or matters of fact. Relations of Ideas are known as a priori knowledge: "discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe" Their truth is necessary: their opposites would be logical impossibilities or contradictions. (tautologies). Matters of Fact require experience: known as a posterioriknowledge, their truth is not necessary: their opposites are not contradictory, they're logically possible. Hume writes:

The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. That the sun will not rise to-morrow is no less intelligible a proposition, and implies no more contradiction than the affirmation, that it will rise.

and

[W]hat is the nature of that evidence which assures us of any real existence and matter of fact, beyond the present testimony of our senses, or the records of our memory[?] (Enquiry IV)

The Epistemological Problem of Induction
What warrants predicting that the sun will rise tommorow if matters of fact are uncertain? We reason by applying what we know of our yesterdays to our tommorrows - in a causal fashion. But of such knowledge we can never be certain.

All reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect. By means of that relation alone we can go beyond the evidence of our memory and senses. (Enquiry IV)

Concerning our Knowledge of Cause and Effect

Cause and effect thinking is not a priori thinking, it is based on experience of constant conjunctions of "cause" and "effect".

I shall venture to affirm, as a general proposition, which admits of no exception, that the knowledge of this [cause-effect] relation. . . arises entirely from experience, when we find that any particular objects are constantly conjoined with each other... When we reason a priori, and consider merely any object or cause, as it appears to the mind, independent of all observation, it never could suggest to us the notion of any distinct object, such as its effect; much less, show us the inseparable and inviolable connexion between them. (Enquiry IV )

The problem with Induction is that our thinking is a bit circular, because we assume that the future will be just like the past. But we can't assume this at all.

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 upon the supposition that the future will be conformable to the past. To endeavour, therefore, the proof of this last supposition by probable arguments, or arguments regarding existence, must be evidently going in a circle, and taking that for granted, which is the very point in question. (Enquiry IV )

Assuming that the future will be just as the past is an unjustifiable assumption. It is not a truth of reason, nor is it a truth of fact. Induction, as Hume saw it, makes very bizarre statements:

The future always has been like the past, in the past.

And

The future will continue to be like the past.

Hume concludes therefore, that our belief in induction has no rational basis -- but only a psychological basis - a "custom or "habit" if you will. This does not mean that our belief is irrational, for there is no logical contradiction inherent in inductive thinking, but it does mean that we appear to be without a rational basis for inductive thinking.

In vain do you pretend to have learned the nature of bodies from your past experience. Their secret nature, and consequently all their effects and influence, may change, without any change in their sensible qualities. This happens sometimes, and with regard to some objects: Why may it not happen always, and with regard to all objects? ...[I]t is not reasoning which engages us to suppose the past resembling the future, and to expect similar effects from causes which are, to appearance, similar. (Enquiry IV)

V. Skeptical Solution to These Doubts
"All inferences from experience, therefore, are effects of custom, not of reasoning." "All these operations are a species of natural instincts, which no reasoning . . . is able either to produce or prevent." (Enquiry V)

Reasonings from experience (or inductions) are not based on reason but instinct or habit or custom.

[I]n all reasonings from experience, there is a step taken by the mind which is not supported by any argument or process of the understanding. (Enquiry V)

The discovery that induction has no rational basis does not cause us to desist from inductive "reasoning". Its basis is instinstinctive, not rational. Hume then suggests a fanciful thought experiment to explore this point futher and in doing so, he creates the "man from outer space" paradigm that we use today. In looking at the acquisition of the  idea of causation, he states:

"Suppose a person . . . brought on a sudden into this world." They would observe succession of objects or events but not the causing or necessitating of one by another. A person suddenly brought into the world] would not, at first, by any reasoning, be able to reach the idea of cause and effect; since the particular powers, by which all natural operations are performed, never appear to the senses; nor is it reasonable to conclude, merely because one event, in one instance, precedes another, that therefore the one is the cause, the other the effect. Their conjunction may be arbitrary & casual. (Enquiry V)

But we, aquainted with the world, assume such a causality. And this thinking has lead to numerous silly superstitions that we clearly recognize as such. Can it be that our present views are equally superstitiuos?

Conclusion: repeated experiences of constant conjunction form the habit or custom of passing from the thought of the first to the second: "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. (Enquiry V)

[Having] observed familiar objects or events to be constantly conjoined together. . . . He immediately infers the existence of one object from the appearance of the other. Yet he has not, by all his experience, acquired any idea or knowledge of the secre power by which the one object produces the other; nor is it by any process of reasoning, he is engaged to draw this inference. (Enquiry V )

VI. Of Probablity
Hume begins this section by denying the reality of chance and thereby appearing to support a strict determinist model of the universe. This is unfortunate, for Hume says many things that appear prescient of quantum theory, and yet with these comments he appears to blow the chance of being seen as a real prescient thinker in following this line of thought (unless of course, quantum theory is eventually refuted...):

Though there be no such thing as Chance in the world; our ignorance of the real cause of any event has the same influence on the understanding, and begets a like species of belief or opinion. (Ignorance leads to specualation which leads us to believing we know something when we do not...)

He notes that the metaphysical probability of anything = 1 or 0, but we in the real world are stuck with only probabilities that lie somewhere in between. Therefore, we can only talk about apparent causes.

Two sorts of apparent causes are the "Universal and the "Probable"

There are some causes, which are entirely uniform and constant in producing a particular effect; and no instance has ever yet been found of any failure or irregularity in their operation. Fire has always burned, and water suffocated every human creature: the production of motion by impulse and gravity is an universal law, which has hitherto admitted of no exception. But there are other causes, which have been found more irregular and uncertain; nor as rhubarb always proved a purge, or opium a soporific to every one, who has taken these medicines. (Enquiry VI)

Therefore, "universal", facts which have been supported through countless experiences and never negated: The Law of universal gravitation holds without exception and probable facts that are backed by evidence, but have been shown to be negated in some situations.

Probable v. Deterministic Reasoning

Hume holds that determinism as a scientific-philosophic assumption is irrelevant to our experience-based inferences.

It is true, when any cause fails of producing its usual effect, philosophers ascribe not this to any irregularity in nature; but suppose, that some secret causes, in the particular structure of parts, have prevented the operation. Our reasonings, however, and conclusions concerning the event are the same as if this principle had no place. (Enquiry VI)

We see that deterministic reasoning is just a special case of probable reasoning where p=1.

Being determined by custom to transfer the past to the future, in all our inferences; where the past has been entirely regular and uniform, we expect the event with the greatest assurance, and leave no room for any contrary supposition. But where different effects have been found to follow from causes, which are to appearance exactly similar, all these various effects must occur to the mind in transferring the past to the future, and enter into our consideration, when we determine the probability of the event. (Enquiry VI)

Causal thinking remains because of it's psychological value, and for its practically: probabilities must serve where certainties don't exist.

VII. Of the Idea of Necessary Connection
Complex ideas, may, perhaps, be well known by definition, which is nothing but an enumeration of those parts or simple ideas, that compose them. But when we have pushed up definitions to the most simple ideas, and find still more ambiguity and obscurity; what resource are we then possessed of? (Enquiry VII)

Hume finds that among the most obscure and uncertain ideas that occur in metaphysics are those very concepts that we rely on the most.

There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion, of which it is every moment necessary for us to treat in all our disquisitions. (Enquiry VII)

He points out that while we see some events preceeding others, that we never observe any force that makes this necessary...

There is not, in any single, particular instance of cause and effect, any thing which can suggest the idea of power or necessary connexion. (Enquiry VII )

We don't observe that B has to follow A, all we observe is just that B does follow A.

"From the first appearance of an object, we can never conjecture what effect will result from it." ... 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 connexion; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other. We only find, that the one does actually, in fact, follow the other. (Enquiry VII )

Hume then states that no impression of necessary force comes from "reflection on our own minds" contradicting both Locke and Berkeley

The motion of our body follows upon the command of our will. Of this we are every moment conscious. But the means, by which this is effected; the energy, by which the will performs so extraordinary an operation; of this we are so far from being immediately conscious, that it must for ever escape our most diligent enquiry. (Enquiry VII)

And that introspection reveals no such thing either.

Hume finds the mind-body interaction mysterious, and wonders how so many other can be certain of a phenomena that no one can directly observe. He puts forth an argument from the incorrigibility & immediacy of reflective awareness...

what the mind is directly perceives (ideas and impressions) are known immediately (no further experience is required) and infallibly or incorrigibly

Hume then uses an argument from anatomy that he will return to later...

How indeed can we be conscious of a power to move our limbs, when we have no such power; but only that to move certain animal spirits, which, though they produce at last the motion of our limbs, yet operate in such a manner as is wholly beyond our comprehension? (Enquiry VII)

The same arguments apply with regard to mind's power to cause motions of ideas or trains of thought - careful introspection doesn't find any such thing:

We only feel the event, namely, the existence of an idea, consequent to a command of the will: but the manner, in which this operation is performed, the power by which it is produced, is entirely beyond our comprehension. (Enquiry VII)

The mind's self-command has limits discoverable only by experience. Presumably here there is "some secret mechanism or structure of parts, upon which the effect depends" (Enquiry VII)

Conclusion: the "necessity" and "force" of which metaphysians speak is incomprensible: experience reveals only frequent or constant conjunction of things not any necessary connection between them.

[W]e only learn by experience the frequent Conjunction of objects, without being ever able to comprehend anything like Connexion between them. (Enquiry VII)

Oddly enough, Hume finds that the idea fault with the idea of Divine Causation in that it makes god seem small, not big. God as a hands on creator is just a deus ex machina. The concept is actually irreligious: better God should delegate or design things so they work by themselves.

It argues more wisdom to contrive at first the fabric of the world with such perfect foresight that, of itself, and by its proper operation, it may serve all the purposes of providence, than if the great Creator were obliged every moment to adjust its parts, and animate by his breath all the wheels of that stupendous machine.(Enquiry VII)

He stresses the point that convoluted arguments carrying us far from common life and experience are untrustworthy.

We are got to fairy land, long ere we have reached the last steps of our theory [of the universal operation of the Supreme Being] (Enquiry VII).

VIII. Of Liberty and Necessity
Some definitions:

Necessity- All events are causally determined; i.e., necessated by antecedent events. Freedom: Some human choices are free. Incompatibility: An event is free only if not causally determined.

Hume puts forth a concept that I agree with - that controvery in matters of freedom and determinism are due to the ambiguous use of words; when the expressions are clarified, arguers often agree.

From this circumstance alone, that a controversy has been long kept on foot, and remains still undecided, we may presume that there is some ambiguity in the expression, and that the disputants affix different ideas to the terms employed in the controversy. (Enquiry VIII)

Concerning necessity, Hume sees two sourcse of the idea:

Our idea, therefore, of necessity and causation arises entirely from the uniformity observable in the operations of nature, where similar objects are constantly conjoined together, and the mind is determined by custom to infer the one from the appearance of the other. These two circumstances form the whole of that necessity, which we ascribe to matter. Beyond the constant conjunction of similar objects, and the consequent inference from one to the other, we have no notion of any necessity or connexion. (Enquiry VIII)

Application to the Free Will Problem

Well, for one thing, the same motives produce the same actions

It is universally acknowledged that there is a great uniformity among the actions of men, in all nations and ages, and that human nature remains still the same, in its principles and operations. The same motives always produce the same actions: the same events follow from the same causes.

And...

A man who at noon leaves his purse full of gold on the pavement at Charing-Cross, may as well expect that it will fly away like a feather, as that he will find it untouched an hour after.

Hume sees in morality the same problems we see in a scientific endeavor: [T]his experienced uniformity in human actions is a source whence we draw inferences concerning them. We are making the same mistakes in the fields of morals as we are in science - as in other cause-effect associations, which give rise by custom to inductive inferences (preditions & generalizations) about people's thoughts and behavior.

[T]his experienced uniformity in human actions is a source whence we draw inferences concerning them.

But we can no more assume the truth of these inferences in the field of morals than we can in the field of science. So we are forced to concede that character & motive necessitate conduct, not universal laws.

It seems almost impossible, therefore, to engage either in science or action of any kind without acknowledging the doctrine of necessity, and this inference from motive to voluntary actions, from characters to conduct.

Hume states that "all mankind have always agreed in the doctrine of necessity according to the foregoing definition and explication of it" He supports this contention by pointing out " how aptly natural and moral evidence link together, and form only one chain of argument."

Seeing the truth in this line of thought, Hume finds a need to examine why the rest of humanity would be resistant to the idea, or...

"why all mankind, though they have ever, without hesitation, acknowledged the doctrine of necessity in their whole practice and reasoning, have yet discovered such a reluctance to acknowledge it in words" But being once convinced that we know nothing farther of causation of any kind than merely the constant conjunction of objects, and the consequent inference of the mind from one to another, and finding that these two circumstances are universally allowed to have place in voluntary actions; we may be more easily led to own the same necessity common to all causes.

Hume sees the same mistaken notion of necessity at work in external cause-effect relations. Yet people feel no such connections in themselves when they voluntarily choose to act or refrain wrongly infer "there is a difference between the effects which result from material force, and those which arise from thought and intelligence" Buttressed by " a false sensation of seeming experience which we have, or may have, of liberty or indifference, in many of our actions"

We feel, that our actions are subject to our will, on most occasions; and imagine we feel, that the will itself is subject to nothing, because, when by a denial of it we are provoked to try, we feel, that it moves easily every way, and produces an image of itself. . . even on that side, on which it did not settle.

Concerning Liberty

By liberty, then, we can only mean a power of acting or not acting, according to the determinations of the will; this is, if we choose to remain at rest, we may; if we choose to move, we also may. Now this hypothetical liberty is universally allowed to belong to every one who is not a prisoner and in chains. Here, then, is no subject of dispute.

Here Hume means to ask if we after making a choice, if we really had the freedom to have acted otherwise. He does not mean a complete acausality - an absolute freedom of uncaused choice. This supposed freedom is madness - randomness, which he again disparages:

And if the definition [of necessity] above mentioned be admitted; liberty, when opposed to necessity, not to constraint, is the same thing with chance; which is universally allowed to have no existence. "[H]ypothetical liberty is universally allowed to belong to everyone who is not a prisoner in chains."

The Moral & Religious Implications of Hume's View

Hume was attacked by theologians such as Beattie and Thomas Reid. They feared the implications of his work, and tended to rely ad hominem attacks (particularly Beattie) and on the logical fallacy of arguing to consequences. He responds thusly:

There is no method of reasoning more common, and yet none more blameable, than, in philosophical disputes, to endeavour the refutation of any hypothesis, by a pretence of its dangerous consequences to religion and morality.

IX. Of the Reason of Animals
All our reasonings concerning matter of fact are founded on a species of Analogy, which leads us to expect from any cause the same events, which we have observed to result from similar causes. ...any theory, by which we explain the operations of the understanding, or the origin and connexion of the passions in man, will acquire additional authority, if we find, that the same theory is requisite to explain the same phenomena in all other animals. (Enquiry IX)

Hume found notable likenesses between humans and animals, both anatomically and behaviorally. He felt that our induction is unconscious or precognitive like theirs

" It seems evident, that animals as well as men learn many things from experience, and infer, that the same events will always follow from the same causes" (Enquiry IX ) The conclusion that Hume draws from this is that we learn much like them - through instince and through the habit-based acquisition of knowledge of the irrational brutes.

and

In all these cases, 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. (Enquiry IX )

However, Hume found notable differences as well.

Due to our possession of language and larger brain we are more self-awares about the learning process, better able to grasp complicated matters, able to chain together much longer inferences, able to form explicit generalizations and capable of far greater information access - through extra-mental devices such as language and writing, we can learn from other's experiences.

Final conclusion: animals are not all that unlike us: they have thought and "knowledge" of matters of fact like ours in kind, although to a lesser extent.

[T]he experimental reasoning itself, which we possess in common with beasts, and on which the whole conduct of life depends, is nothing but a species of instinct or mechanical power, that acts in us unknown to ourselves; and in its chief operations, is not directed by any such relations or comparisons of ideas, as are the proper objects of our intellectual faculties. (Enquiry IX)

X. Of Miracles
A famous chapter in Hume's work.

[A] weaker evidence can never destroy a stronger. A wise man, therefore, proportions his belief to the evidence. In such conclusions as are founded on an infallible experience, he expects the truth the event with the last degree of assurance, and regards his past experience as a full proof of the future existence of that event. In other cases, he proceeds with more caution: He weighs the opposite experiments: He considers which side is supported by the greater number of experiements: to that side he inclines, with doubt and hesitation: and when at last he fixes his judgement, the evidence exceeds not what we proberly call probability. (Enquiry X)

Hume saw correctly that miracles are violations of the laws of nature. To  den this and call them natural acts is to redefine the word out of utility.

A miracle may be accurately defined a transgression of a law of nature by a particular volition of the Deity, or by the imposition of some invisible agent.

Since the laws of nature are based on literally trillions of observations by billions of people, miracles are events of the utmost improbability. Therefore, second hand testimony of miracles is always more likely to be false..

''[N]o testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavors to establish. (Enquiry X)''

...particularly when we recognize the problems of human credulity, misapprehension, and dishonesty. (Recall that the catholic church even supported deception for the sake of religious matters.) When we take into consideration what some devout religious people might do to support their wish filled beliefs, we see that we need extraordinary evidence to support extraordinary propositions.

There must, therefore, be a uniform experience against every miraculous event, otherwise the event would not merit that appellation.

Conclusion: Reports of miracles are never beliefworthy

''[I]f the spirit of religion join itself to the love or wonder, there is an end to common sense; and human testimony, in thse cirucumstances, loses all pretensions to authority. ...[n]o human testimony can have such force as to prove a miracle and make it a just foundation for any system of religion" (Enquiry X)''

Caveat: Hume's argument appears to begin with a probabistic declaration that weaker evidence cannot prevail over strong evidence (which is reasonable and uncontroversial) and appears to conclude that miracle reports are never trustworthy. This is often read as a negative universal categorical statement, which in turn would appear to rule  out out miracles a-priori. If this is the case then Hume's conclusion does not follow from his argument. In "Hume's Abject Failure" John Earman identifies and attempts to explain what he believed contributed to Hume's error: an inadequate understanding of inductive argumentation (following up a set of inductive claims with a deductive conclusion) and  a lack of an existing probability theory  (I.e. such as Bayesian theory).

However, the Hume Society responded to Earman's claims by stating that Hume's conclusion only ruled out a posteriori methodology's ability to affirm miracles. http://www.humesociety.org/hs/issues/v28n1/levine/levine-v28n1.pdf   They point out that Earman's points against Hume are not original (making Earman's own claim of the unoriginality of Hume ironic) and that there is disagreement as to whether Hume's argument is deductive or inductive.

What a mess!

Conclusion:  I would still argue that Hume's argument ends with too strong a claim as it still appears to argue that it is impossible to observe a miracle. I'd say a rain of Bibles over the planet accompanied by Handel's 'Messiah' would at least point to the possibilty of the supernatural!

While Hume's message about the doubtful quality of miracle reports remains a helpful epistemological guide, his conclusion should be rejected. Ruling out miracle reports a priori or even a posteriori is not only illogical it is unnecessary. To say: Extraordinarly claims require extraordinary evidence suffices.

XI. Of a Particular Providence and of a Future State
The Design Argument states that there is order and structural design in nature and then argues that nothing but the deliberate work of an intelligent creator could have made something so orderly and well-structured. Therefore therefore nature (or the world) be the product of God, an infiinitely powerful, good, and intelligent Designer. (What a leap in logic!)

You. . . have acknowledged, that the chief or sole argument for a divine existence. . . is derived from the order of nature; where there appear such marks of intelligence and design, that you think it extravagant to assign for its cause, either chance, or the blind and unguided force of matter. You allow, that this is an argument drawn from effects to causes. From the order of the work, you infer, that there must have been project and forethought in the workman. If you cannot make out this point, you allow, that your conclusion fails; and you pretend not to establish the conclusion in a greater latitude than the phenomena of nature will justify. (Enquiry XI)

Further Critique of the Design Argument
"When we infer any particular cause from an effect, we must proportion the one to the other, and can never be allowed to ascribe to the cause any qualities, but what are exactly sufficient to produce the effect." (Enquiry XI)

Hume notes some rather clear and obvious realities that deny the argument further. He notes that the natural world is finite and imperfect. Therefore, we are at most warranted in inferring a finite & imperfect creator: not God. In other words, to take the theist at his word, he must infer from our imperfect world that there can be not perfect god.

The knowledge of the cause being derived solely from the effect, they must be exactly adjusted to each other; and the one can never refer to anything farther, or be the foundation of any new inference and conclusion show only the need to assign a designer intelligent enough to create so much order as actually exist. (Enquiry XI

XI. Of the Academical of Sceptical Philosophy
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 (Enquiry XII).

Two species of skepticism distinguished:

Hume first tears to pieces Cartesian doubt, which he refers to as "antecedant skepticism" or skepticism before we observe, which "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" (Enquiry XII) And he is basically right. As a psychologist, I have learned that a patient who believes that he does not exist (extreme nihlism) is exceedingly difficult to help.

Hume then puts forth "consequent" skepticism, the skepticism natural to science and enquiry. But Hume maintains that this skepticism is also an unattainable ideal -- nature is too strong.

Casting aside these two impossible ideals, Hume puts forth two modes of knowledge, which he holds as forms of moderate skepticism. A priori knowledge of relations of ideas: known with certainty: limited to mathematics. And "knowledge" of matters of fact: uncertainly based on experience: science and common sense.

Hume goes rather hard against the pretensions of metaphysics in giving us knowledge of matters of fact :

If we take into 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. Consign it then to the flames: For it can contain nothing but sophistry and illusion. (Enquiry XII )

(Well, we would be better off without such nonsense, but let's leave book burning to the christians.)

He even questions their ability to give us knowledge of the external world...

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. (Enquiry XII)

or how it came about... (the concept of ex nihilo nihil fit )

That impious maxim of the ancient philosophy, Ex nihilo, nihil fit, by which the creation of matter was excluded, ceases to be a maxim, according to this philosophy. Not only the will of the supreme Being may create matter; but, for aught, we know a priori, the will of any other being might create it, or any other cause, that the most whimsical imagination can assign. (Enquiry XII)

He lastly questions their ability to give us knowledge of objective moral values, saying that morals...

and criticism are not so properly objects of the understanding as of taste and sentiment. (Enquiry XII)

Summary
. As Socrates said, the wise man knows what he does not know, and Hume clearly fits the bill.