Book Summary: An Enquiry Concerning Human Understanding / David Hume

Section I: Of the Different Species of Philosophy

According to Hume, “moral philosophy, or the science of human nature, may be treated after two different manners” (p.1). The first type of philosophical thinking he refers to is one that considers man born for action, considers his taste and sentiment, borrows help from poetry and eloquence, and treats its subjects in an easy and obvious way, making us feel the difference between vice and virtue. The second species of philosophers consider man as more of a reasonable rather than an active being, focusing on abstract speculations, make things unintelligible to common readers. Hume calls these “easy and obvious philosophy” and “accurate and abstruse philosophy” respectively. He prefers the former one to the latter one as it enters more into common life, molds the heart and affections, and bring man closer to perfection; while the latter “vanishes when the philosopher leaves the shade, and comes into open day” (p.3).

Hume also has in his mind an ideal character of a philosopher. According to him, a philosopher ought to have a moderate character, at times enjoying company and the conversations of other and at other times retaining a taste for books. “Man is a sociable, no less than a reasonable being […] Indulge your passion for science but let your science be human […] Be a philosopher; but, amidst all your philosophy, be still a man” (p.5)

Hume notes that abstract philosophy too has its uses and can be a significant aid in doing easy and obvious philosophy. “The politician will acquire greater foresight and subtlety, in the subdividing and balancing of power; the lawyer more method and finer principles in his reasonings; and the general more regularity in his discipline, and more caution in his plans and operations” (p.7). This doesn’t prevent Hume from being critical of the abstruse philosophy as he sees some of their efforts, such as “superstitious” ones on metaphysics, arise from fruitless efforts of human vanity. “In vain do we hope, that men, from frequent disappointment, will at last abandon such airy sciences, and discover the proper province of human reason […] The only method of freeing learning, at once, from these abstruse questions, is to inquire seriously into the nature of human understanding, and show, from an exact analysis of its powers and capacity, that it is by no means fitted for such remote and abstruse subjects” (p.9).

Section II: Of the Origins of Ideas

According to Hume, the perceptions of the mind can be divided into two classes, one is ideas and the other is impressions. Impressions “are more lively perceptions, when we hear, or see, feel, or love, or hate, or desire, or will. And impressions are distinguished from ideas, which are the less lively perceptions, of which we are conscious when we reflect on any of those sensations or moments” (p.16). And “all our ideas or more feeble perceptions are copies of our impressions or more lively ones” (p.17). So, all thinking are derived from our inward or outward sentiment. “When we think of a golden mountain, we only joint two consistent ideas, gold and mountain, with which we were formerly acquainted” (p.17). Hume has two arguments to prove his claim.

First, “when we analyse our thoughts or ideas, however compounded or sublime, we always find that they resolve themselves into such simple ideas as were copied from a precedent feeling or sentiment. Even those ideas, which, at first view, seem the most wide of this origin, are found, upon a nearer scrutiny, to be derived from it” (p.17). As an example, our idea of God “arises from reflecting on the operations of our mind, and augmenting, without limit, those qualities of goodness and wisdom” (p.17) — such as ‘all-knowing’, or ‘all-hearing’. Secondly, “a blind man can form no notion of colours; a deaf man of sounds. Restore either of them that sense in which he is deficient by opening this new inlet for the ideas; and he finds no difficulty in conceiving these objects” (p.18). Hume, sees colours as an exception, because although we may not have seen a certain shade of a colour, we can still imagine what it looks like if if it stands as a blank in scale of the shades of a colour, descending from lightest to deepest.

Section III: Of the Association of Ideas

In this section, Hume introduces us the three principles of connections among ideas: resemblance (a picture naturally leads our thoughts to the original), contiguity in time or place (the mention of one apartment in a building naturally introduces an inquiry or discourse concerning others), and cause or effect (if we think of a wound, we can scarcely forebear reflecting on the pain which it follows). All other connections are a different mixture of these elements. For example, contrast is a mixture of causation and resemblance.

Section IV: Sceptical Doubts Concerning the Operations of the Understanding

All the objects of human reason or inquiry may be divided into two kinds, to wit, relations of ideas, and matters of fact” (p.23). Relations of ideas are propositions like ‘three times five is equal to the half of thirty’ or ‘the square of the hypothenuse is equal to the squares of the two sides’, which “are discoverable by the mere operation of thought, without dependence on what is anywhere existent in the universe” (p.24). On the other hand, matters of fact are based on our experiences and their truth about the future cannot be known. “That the sun will not rise tomorrow is no intelligible a proposition, and implies no more contradiction than affirmation, that it will rise” (p.24).

All reasonings concerning matter of fact seem to be founded on the relation of cause and effect” (p.25). For example, you may believe that a friend is in France by the fact that you received a letter from him. However, the cause of any event is not known a priori but arises entirely from experience. We cannot discover the relation between causes and effects by reason but by only experience. No one can discover a priori the explosion of gunpowder. We can’t have any a priori explanation of where a billiard ball would go once it gets hit by another one, without the influence of our custom of the mysterious laws of nature, which we perceive through experience. “Every effect is a distinct event from its cause. It could not, therefore, be discovered in the cause, and the first invention or conception of it, a priori, must be entirely arbitrary” (p.29).

Since all causes and effects are known by our past experience and not reason, and since there is nothing that assures us that the same relations of causes and effects will hold the future as well, then it is impossible for us to prove our predictions of the past, which are merely based on an inductive reasoning. Thus, Hume accepts the difficulty he faces in constructing an argument for a rational basis for causal reasoning and challenges others to tackle the problem.

Section V: Sceptical Solutions of These Doubts

In this section, Hume focuses on the notion of customs and habits which, in our minds, link causes and effects to make guesses about the future. “All inferences from experience, therefore, are effects of custom, not of reasoning. Custom, then, is the great guide of human life. It is that principle alone which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past” (p.45-46).

Likewise, imagination too is strongly linked to our experience, although it has “unlimited power of mixing, compounding, separating, and dividing these ideas, in all the varieties of fiction and vision” (p.49). Here, Hume touches upon the differences between fiction and belief. “Belief is something felt by the mind, which distinguishes the ideas of the judgement from the fictions of the imagination” (p.52).

Section VI: Of Probability

According to Hume, there is no such thing as chance but that a belief of chance as a result of us not truly understanding the causes. “It is more probable, in almost every country of Europe, that there will be frost sometime in January, than that the weather will continue open throughout the whole month; though this probability varies according to the different climates, and approaches to a certainty in the more northern kingdoms. Here then it seems evident, that, when we transfer the past to the future, in order to determine the effect, which will result from any cause, we transfer all the different events, in the same proportion as they have appeared in the past, and conceive one to have existed a hundred times, for instance, another ten times, and another once. As a great number of views do here occur in one event, they fortify and confirm it to the imagination, beget that sentiment which we call belief, and give its object the preference above the contrary event, which is not supported by an equal number of experiments, and recurs not so frequently to the thought in transferring the past to the future” (p.61-62).

Section VII: Of the Idea of Necessary Connection

Hume suggests that “there are no ideas, which occur in metaphysics more obscure and uncertain, than those of power, energy, or necessary connection, of which it is every moment necessary for us to treat in all our disquisitions” (p.64). And reminds of his argument that “all our ideas are nothing but copies of our impressions” (p.65), and that all complex ideas and impressions are a combination of simple ones which are based on our vivid experience of the world. So, Hume traces the idea of causation to its roots of impressions that it is derived from.

When we look into the interactions between different bodies and “consider the operation of causes, we are never able, in a single instance, to discover any power or necessary connection; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other” (p.66). So, from merely looking at the interactions between billiard balls, “it is impossible, therefore, that the idea of power can be derived from the contemplation of bodies” (p.67). Hume then moves from body-body interactions to mind-body interactions. He specifically looks into the influence of volition over the organs of the body and how we can move some of our organs with our will and not some other organs (like the heart). “We learn the influence of our will from experience alone. And experience only teaches us, how one event constantly follows another; without instructing us in the secret connection, which binds them together, and renders them inseparable” (p.69).

Lastly, Hume looks into mind-mind interactions which he fails to find a connection. Firstly, he wonders at the existence of an idea from nothing. “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” (p.72). Secondly, “the command of the mind over itself is limited, as well as its command over the body; and these limits are not known by reason, or any acquaintance with the nature of cause and effect, but only by experience and observation” (p.72). And thirdly, “this self-command is very different at different times. A man in health possesses more of it than one languishing with sickness” (p.72).

Hume also attacks occasionalist philosophers who believe that “those objects which are commonly denominated causes, are in reality nothing but occasions; and that the true and direct principle of every effect is not any power or force in nature, but a volition of the Supreme Being, who wills that such particular objects should forever be conjoined with each other. Instead of saying that one billiard ball moves another by a force which it has derived from the author of nature, it is the Deity himself, they say, who, by a particular volition, moves the second ball” (p.74). Hume objects to this idea by saying that it is a too bold of a statement and writes the following, “I cannot perceive any force in the arguments on which this theory is founded. We are ignorant, it is true, of the manner in which bodies operate on each other: their force or energy is entirely incomprehensible; but are we not equally ignorant of the manner or force by which a mind, even the supreme mind, operates either on itself or on body?” (p.77).

Hume then proceeds to suggest that “one event follows another; but we never can observe any tie between them. They seem conjoined; but never connected. […] the necessary conclusion seems to be that we have no idea of connection or power at all” (p.78). But Hume then takes a positive turn in his skepticism to argue that “it appears, then, that this idea of a necessary connection among events arises from a number of similar instances which occur of the constant conjunction of these events; nor can that idea ever be suggested by any one of these instances, surveyed in all possible lights and positions. […] after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe that it will exist. […] When we say, therefore, that one object is connected with another, we mean only that they have acquired a connection in our thought, and give rise to this inference, by which they become proofs of each other’s existence: a conclusion which is somewhat extraordinary, but which seems founded on sufficient evidence” (p.80-81). So, “the only immediate utility of all sciences, is to teach us, how to control and regulate future events by their causes” (p.82).

Section VIII: Of Liberty and Necessity

Hume writes about have there have been many disputes over the concepts of ‘liberty’ and ‘necessity’ and believes that such disputes could come to an end if people tweaked their definitions more carefully.

Hume, again, reminds us that “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” (p.88). Hume applies the same logic seen in nature to humans too. “It is universally acknowledged that there is a great uniformity among the actions of men, in all nations and ages, in its principles and operations. The same motives always produce the same actions; the same events follow from the same causes” (p.88). “We must now, however, expect that this uniformity of human actions should be carried to such a length as that all men, in the same circumstances, will always act precisely in the same manner, without making allowance for the diversity of characters, prejudices, and opinions. Such uniformity in every particular, is found in no part of nature” (p.91). He further argues that it would be almost impossible to engage in science of any form or action of any kind without acknowledging the doctrine of necessity and the inference from motive to voluntary actions, from characters to conduct.

Hume then formulates his own definition of liberty. “By liberty, then, we can only mean a power of acting or not acting, according to the determinations of the will; that is, if we choose to remain at rest, we may; if we choose to move, we also may” (p.103). And ultimately argues that the concepts of liberty and necessity does not have to contradict each other.

Hume then takes his thought to the domain of morality. “I frankly submit to an examination of this kind, and shall venture to affirm that the doctrines, both of necessity and of liberty, as above explained, are not only consistent with morality, but are absolutely essential to its support” (p.105). He explains that our actions are based on certain motives. “All laws being founded on rewards and punishments, it is supposed as a fundamental principle, that these motives have a regular and uniform influence on the mind, and both produce the good and prevent the evil actions” (p.106). Actions are regarded good or bad depending on the cause that leads to them. So, if we are to deny liberty, then we would not be blamed for any of our actions and move away from a uniformity of moral practices.

Hume also faces two arguments regarding the idea that it is God that is the sole creator of our actions. “First, that, if human actions can be traced up, by a necessary chain, to the Deity, they can never be criminal; on account of the infinite perfection of that Being from whom they are derived, and who can intend nothing but what is altogether good and laudable. Or, Secondly, if they be criminal, we must retract the attribute of perfection, which we ascribe to the Deity, and must acknowledge him to be the ultimate author of guilt and moral turpitude in all his creatures” (p.109). When it comes to the first argument, Hume counters this objection by saying that our moral speculations are not metaphysical but are founded in the natural sentiments of the human mind. When it comes to the second one, Hume objects by saying that “to reconcile the indifference and contingency of human actions with prescience; or to defend absolute decrees, and yet free the Deity from being the author of sin, has been fond hitherto to exceed all the power of philosophy” (p.112).

Section IX: Of the Reason of Animals

In this part, Hume argues that we learn by analogically observations and that this argument is supported when we investigate animals — offering two points. “First, 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. […] Secondly, It is impossible, that this inference of the animal can be founded on any process of argument or reasoning, by which he concludes, that like events must follow like objects, and that the course of nature will always be regular in its operations. […] Animals, therefore, are not guided in these inferences by reasoning; neither are children; neither are the generality of mankind, in their ordinary actions and conclusions” (p.114-115).

Section X: Of Miracles

Hume defines a miracles as “a violation of the laws of nature” (p.124) and argues that there must “be a uniform experience against every miraculous event, otherwise the event would not merit that appellation” (p.125). Then Hume provides four reasons on why, according to him, within the domains of reason, “there never was a miraculous event established on so full an evidence” (p.126).

“For first, there is not to be found, in all history, any miracle attested by a sufficient number of men of such unquestioned good sense, education, and learning, as to secure us against all delusion in themselves; of such undoubted integrity, as to place them beyond all suspicion of any design to deceive others” (p.126-127). Second, “the passion of surprise and wonder, arising from miracles, being an agreeable emotion, gives a sensible tendency towards the belief of those events from which it is derived” (p.127-128). “Thirdly. It forms a strong presumption against all supernatural and miraculous relations, that they are observed chiefly to abound among ignorant and barbarous nations” (p.130). Fourthly, “there is no testimony for any, even those which have not been expressly detected, that is not opposed by an infinite number of witnesses; so that not only miracle destroys the credit of testimony, but the testimony destroys itself” (p.132). Thus, since “religion is founded on faith, not on reason” (p.142), “the Christian Religion not only was first attended with miracles but even at this day cannot be believed by any reasonable person without one. Mere reason is insufficient to convince us of its veracity: and whoever is moved by faith to assent to it, is conscious of a continued miracle in his own person, which subverts all the principles of his understanding, and gives him a determination to believe what is most contrary to custom and experience” (p.144).

Section XI: Of a Particular Providence and of a Future State

In this section, Hume narrates his conversation with a friend concerning the the inference of God via cause-effects. According to Hume’s explanation, the conversation began by Hume talking about his admiration of Ancient Greece and Rome where an entire liberty was given to philosophy and was not countered by religious thinking. His friend delivers an imaginary speech from an Epicurus who does philosophy despite the arguments coming from religious traditions. His friend says how religious philosophers have strayed from the path of philosophy “in trying how far they can establish religion upon the principles of reason” (p.148). Hume presents how religious philosophers reason for the existence of God by presenting the uniformity and beauty in all cause and effects — hence arguing for a divine design. But Hume’s friend objects by saying that this is a product of imagination, rather than reason.

Hume then gives an example of how “the print of a foot in the sand can only prove, when considered alone, that there was some figure adapted to it, by which it was produced: but the print of a human foot proves likewise, from out other experience, that there was probably another foot, which also left its impression, though effaced by time or other accidents. Here we mount from the effect to the cause, infer alterations in the effect; but this is not a continuation of the same simple chain of reasoning. We comprehend in this case a hundred other experiences and observations, concerning the usual figure and members of that argument must be considered as fallacious and sophistical” (p.159). On the other hand, “The deity is known to us only by his productions, and is a single being in the universe, not comprehended under any species or genus” — thus, according to him, the case is not the same with our reasonings from the works of nature. “The great source of our mistake in this subject, and of the unfounded license of conjecture, which we indulge, is, that we tacitly consider ourselves, as in the place of the Supreme Being, and conclude that he will, on every occasion, observe the same conduct, which we ourselves, in his situation, would have embraced as reasonable and eligible” (p.160).

So, “all the philosophy, therefore, in the world and all the religion, which is nothing but a species of philosophy, will never be able to carry us beyond the usual course of experience, or give us measures of conduct and behaviour different from those which are furnished by reflections on common life. No new fact can ever be inferred from the religious hypothesis; no event foreseen or foretold; no reward or punishment expected or dreaded, beyond what is already known by practice and observation” (p.161).

Section XII: Of the Academically or Sceptical Philosophy

Hume explains that there are two types of skepticism, antecedent and consequent skepticism. Antecedent skepticism “is much inculcated by Descartes and others, as a sovereign preservative against error and precipitation judgment. 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 possible be fallacious or deceitful” (p.164-165). This is the extreme form of this form of skepticism, while Hume suggests that there is a moderate form of it which “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” (p.165).

“There is another species of scepticism, consequent to science and inquiry, when men are supposed to have discovered either the absolute fallaciousness of their mental faculties, or their unfitness to reach any fixed determination in all those curious subjects of speculation, about which they are commonly employed” (p.165). Our perception of the external world can be deceiving, or the mind itself can be deceived by dreams, madnesses or other diseases. We can only justify our perception of the external world through our experience that we gain through our sense, but our senses can always be called to question. So, our belief in the external world cannot be rationally proved.

According to Hume, the existence of any being cant only be proved by arguments from its cause or its effect. “Whatever is may not be. No negation of a fact can involve a contradiction. The non-existence of any being, without exception, is as clear and distinct an idea as its existence. The proposition, which affirms it not to be, however false, is no less conceivable and intelligible, than that which affirms it to be” (p.181). Hume then reminds us again that the best and most solid foundation of Divinity or Theology is faith rather than reason. And adds that “beauty, whether moral or natural, is felt, more properly than perceived” (p.182).

Hume ends the book with the following, “When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing by sophistry and illusion” (p.183).

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