Notes on Hume's Treatise of Human Nature
by G. J. Mattey

Abstract

"An Abstract of a Book lately Published, entitled, A Treatise of Human Nature, &c., Wherein the Chief Argument of that Book is Farther Illustrated and Explained" was published anonymously by Hume in 1739 or 1740, after disappointing reviews of the Treatise.

1. The Treatise seems to have followed the "plan" of English philosophers over the last forty years, in which they "seem even to have started a new kind of philosophy, which promises more both to the entertainment and advantage of mankind, than any other with which the world has been yet acquainted." The old kind of philosophy is that of the ancients. When they treat of human nature, most of these writers do no more than to represent "the common sense of mankind in the strongest lights, and with the best turn of thought and expression." By contrast, the latest writers show a "depth of reasoning and reflection," wherein they follow out chains of propositions and put together "a regular science." They have been very successful in the philosophy of nature. There is every reason to believe that the philosophy of man can be equally successful. The method is to examine various phenomena and "resolve" them into common principles, which themselves depend on a "few simple principles." If this can be done, we will be satisfied in our knowledge as much as we can be, since "we can never arrive at the ultimate principles."

2. The author of the Treatise seems, like his recent predecessors, to follow this method. The goal is to provide an anatomy of human nature, according to the following constraints:

• To draw conclusions only when warranted by experience.
• To refrain from giving explanations based on hypotheses that cannot be confirmed by experience.

3. Human nature is what "most nearly concerns us," and a science of human nature would afford us satisfaction. But there is another benefit of such a science: in that it comprehends "almost all the sciences." Specifially:

• Logic is only about "the principles and operations of the reasoning faculty and the nature of our ideas."
• Morals and Criticism is about our "tastes and sentiments."
• Politics is about the union of men in society and their dependence on one another.

4. Leibniz [in Theodicy, "Preliminary Dissertation on the Conformity of Faith with Reason, Section 31] has criticized the logic of Locke [An Essay Concerning Human Understanding], Malebranche [The Search for the Truth], and Arnauld [The Art of Thinking] for neglecting to treat of probable reasoning. This is very unfortunate, as reasoning about probability is our guide to life, as well as something that is used in most philosophical speculation. The author of the Treatise has noted this deficiency and tried to overcome it. The book "contains a great number of speculations very new and remarkable," so that it is impossible here to give an adequate account of the whole. Instead, an account of "reasonings from cause and effect" will be discussed here and might serve as a "specimen of the whole."

5. The book begins with definitions:

• Perception: "whatever can be present to the mind, whether we employ our senses, or are actuated with passion, or exercise our thought and reflection."
  • Impression: either a feeling of passion or emotion, or the image of external objects conveyed by our senses.
  • Idea: the result of reflecting on a passion or object that is not present.

6. The first proposition of the Treatise is that all ideas ("weak perceptions") are derived from impressions ("strong perceptions"). All that we can think about is what we have seen without us or have felt within our own minds. This is apparently equivalent to Locke's rejection of innate ideas in favor of the claim that all ideas arise from experience. But as Locke calls all perceptions (not merely weak ones) "ideas," he is wrong, as impressions are innate, as are the passions, which arise immediately from nature. [See the Enquiry concerning the Understanding, Section 2, footnote 1, where 'innate' is taken to mean 'natural' or 'original.' Hume maintains there that it is frivolous to think of 'innate' as meaning 'contemporary to our birth.'] Malebranche could not find any thought of the mind which was not derived from something felt beforehand, internally or externally. So his view can be reconciled with that of the author. So can the view of Locke, who would readily acknowledge that passions are a kind of natural instinct derived from the human constitution.

7. The author has found two principles that can be used to decide controversies over ideas:

• Ideas are always preceded by impressions.
• Ideas always appear first as impressions.

8. All reasonings concerning matters of fact are based on the relation of cause and effect. We can never infer the existence of one object from that of another without their being connected. So to understand this reasoning, we must analyze the idea of a cause. To do this, we must find an example of a cause.

9. The case of a billiard ball, which is at rest until being struck by another billiard ball and then begins moving, is "as perfect an instance of the relation of cause and effect as any which we know, either by sensation or reflection." We observe the following in the case:

• The two balls are contiguous in place and time.
• The two balls touched before the motion began.
• There was no time ("interval") between when they touched and when the motion began.
• The cause is prior to the effect.
• The motion of the moving ball occurred before the motion of the ball it struck.
• There is a constant conjunction between the cause and the effect. "Every object like the cause produces always some object like the effect."
• With any other balls "of the same kind in a like situation," "the impulse of the one produces motion in the other."

10. The above is what is observed when both cause and effect are "present to the senses." When inference is involved, we move from observation of the effect to the conculsion that the cause has existed, or from observation of the cause to the conclusion that the effect will exist. If we perceive the motion of one ball, we immediately conclude that they will collide, and that second ball will move. "This is the inference from cause to effect; and of this nature are all our reasonings in the conduct of life: on this is founded all our belief in history: and from hence is derived all philosophy, excepting only geometry and arithmetic." If we can understand the inference we make concerning the behavior of the balls upon impact, we can understand all our causal inferences.

11. It might be thought that reason sees something in the cause that makes us infer to the effect. But suppose that there were a person, Adam, who has "the full vigour of understanding" but was totally lacking in experience. Exercise his reason as he will, "he would never be able to infer the motion in the second ball from the motion and impulse of the first." If he could make the inference, it would be a demonstration which was based wholly on the comparison of his ideas of the two balls. "But no inference from cause to effect amounts to a demonstration." An "evident proof" can be given of this fact. The mind is always able to conceive of any event following from a given cause, and more strongly, any event following from any other event. What is conceivable is at least metaphysically possible. When there is a demonstration, the contrary of the conclusion is impossible and "implies a contradiction." No conjunction of cause and effect can be demonstrated, "And this is a principle, which is generally allowed by philosophers."

12. So how could Adam come to make the inference from the observation of the motion of the first ball to conclusion of the motion of the second? God could inspire him to make it. But barring that, he would have had to have experienced, "in several instances," the conjunction of the motion of the first ball, the impact, and the motion of the second. With enough repetition of this kind of experience, he would "always conclude without hesitation" that the second ball would move. "His understanding would anticipate his sight, and form a conclusion suitable to his past experience."

13. "It follows, then, that all reasonings concerning cause and effect are founded on experience." Moreover, it also follows that all reasoning from experience depends on supposing "that the course of nature will continue uniformly the same." But why do we suppose the uniformity of nature?

14. The claim that the course of nature will continue uniformly the same cannot be demonstrated by "Adam with all his science" [or by anyone else]. It is conceivable that the course of nature not continue to be uniform, and (as noted in paragraph 11) what is conceivable is metaphysically possible. But the denial of the conclusion of a demonstration must be metaphysically impossible. Moreover, the uniformity of nature cannot be proved by probable arguments. For all probable arguments are based on the supposition that nature is uniform. Thus, one would have to suppose that nature is uniform in order to prove that nature is uniform, which cannot be done. To be sure, the uniformity of nature is a matter of fact, that could only be proved, if at all, by appeal to experience. But experience can used in a proof only on the supposition of that there is a resemblance between past and future. "This therefore is a point, which can admit of no proof at all, and which we take for granted without any proof."

15. Since we cannot prove the supposition of uniformity, why do we make it in the first place? The answer is that "we are determined by CUSTOM alone to suppose the future conformable to the past." For example, it is habit that leads my mind to "anticipate my sight by conceiving" the motion of the second ball when I see that of the first. "There is nothing in these objects, abstractly considered, and independent of experience, which leads me to form any such conclusion." And even after much experience, there is still no argument to this effect, because it depends on the supposition "that the effect will be conformable to past experience." We do not know the powers by which bodies operate, as we only perceive their sensible qualities. "And what reason have we to think, that the same powers will aways be conjoined with the same sensible qualities?"

16. Thus custom, and not reason, is the guide to life. Only custom can be the basis of the supposition that leads to our expectations. "However easy this step may seem, reason would never, to all eternity, be able to make it."

17. The discovery that custom determines our mind to anticipate the effects of causes is "very curious," but it "leads us to others, that are still more curious." The psychological result of observing the motion of the first ball is described as an anticipation of sight by conceiving the second ball in motion. But conceiving is not all we do: in addition we believe that the ball will move. "What then is this belief? And how does it differ from the simple conception of any thing? Here is a new question unthought of by philosophers."

18. In the case of demonstration, one realizes that the denial of the conclusion is impossible, since it implies a contradiction. But where one relies on experience to prove a matter of fact, the contrary of the conclusion is always possible, no matter how strong the proof is. Still, one believes the conclusion. "The belief, therefore, makes some difference betwixt the conception to which we assent, and that to which we do not assent."

19. There are only two hypotheses that would account for this difference between belief and conception:

• Belief joins new ideas to unbelieved conceptions.
• Belief is nothing more than a different manner of conceiving.

20. The second reason why the first hypothesis is false is that, contrary to experience, we would be able to believe anything we please simply by adding the requisite idea to the original conception. And we can add together any ideas we please, so long as they do not result in a contradiction.

21. Since belief requires a conception but is something more than a conception, the only alternative is that it is a different way of conceiving: "something that is distinguishable to the feeling, and depends not upon our will, as our ideas do." In the case of the billiard balls, before the moment of impact, the mind "feels something different in the conception of [the second ball] from a mere reverie of the imagination." The behavior of the first ball, along with the constant conjunction found in experience, make the idea of the second feel different "from those loose ideas, which come into the mind without any introduction." Although this result is surprising, it is based on "a chain of propositions which admit of no doubt." The reasoning is then summarized, but the summary will not be repeated here.

22. The next point is to explain the feeling that differentiates belief from loose conception. Although it is impossible to describe by words the feeling "which every one must be conscious of in his own breast, the author uses a number of expressions to describe the fact that belief "has a more forcible effect on the mind than fiction and mere conception." Belief is:

• Stronger.
• More lively.
• More vivid.
• Firmer.
• More intense.

23. The next task is to explain the cause of the lively feeling. This is done by making "an analogy with other acts of the mind." The reasoning "seems to be curious," but describing it properly would require too much detail. [See Book I, Part III, Section 8.]

24. Many arguments of the author to prove that belief is nothing more than a lively conception are omitted here. But one will be described. Experience is not entirely uniform. Anyone who has watched billiards has seen that sometimes the cue ball continues moving at impact and somtimes it stops, depending on whether it was struck straight-on or with backspin. But most often, the cue ball keeps moving, and so we have a feeling that it will move. So as far as the two conceptions (cue ball moving or cue ball stopped), "were not the one conception different in the feeling or sentiment from the other, there would be no difference betwixt them." [This happens frequently in golf, where a player will be very surprised that his ball stopped upon hitting the green, as he expected it to keep moving. He could conceive of both outcomes, but he feels that it will continue to move.]

25. Although the illustration of causal reasoning has been confined to matter in motion, it applies equally well to the operations of the mind. We cannot tell from a consideration of our willing that a certain effect will take place. And even after experience, only custom dictates what we will expect. Habit leads to the belief in the effect, and the belief is only a more intense conception.

26. After having explained the nature of the inference from cause to effect and vice-versa, the author returns to the idea of the relation of cause and effect. It was seen in paragraph 9 that the only components of the relation are contiguity, precedence, and constant conjunction. However, it is commonly supposed that the there is another factor in a cause, which might be called "power," or "force," or "energy." As seen in paragraph 7, these terms must be tested, first by asking what idea attaches to them, and then what impression is the source of the idea. "If all our thoughts be derived from impressions, this power must either discover itself to our senses, or to our internal feeling." But it does neither. The senses do not detect power, and indeed followers of Descartes held that there is no power at all in matter. They attributed all change in matter to power in God. But then the question arises as to our idea of divine power. [For example, Malebranche states, "The author of nature is the universal cause of all motion found in matter," The Search After Truth, Book One, Chapter One.] If innate ideas [i.e., ideas we possess at birth] be denied, then this idea is "nothing but a composition of those ideas, which we acquire from reflecting on the operations of our own minds." But our own minds do not supply the needed idea any more than matter does. We cannot infer any effects of our will in the absence of experience, and when we take experience into account, all we find is contiguity, precedence, and constant conjunction. "Upon the whole, then, either we have no idea at all of force and energy, and these words are altogether insignificant, or they can mean nothing but that determination of the thought, acquired by habit, to pass from the cause to its usual effect." We must conclude that "there is some difficulty in the case, and . . . whoever solves the difficulty must say some thing very new and extraordinary; as new as the difficulty itself."

27. The philosophy is very skeptical, presenting a view of an imperfect and narrowly limited human understanding. A further skeptical conclusion is that belief in external existence or existence after perception is based on nothing more a lively conception based on habit. "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 wou'd render us entirely Pyrrhonian [i.e., lacking in beliefs altogether], were not nature too strong for it."

28. Another opinion peculiar to the author (as are most of his opinions) is that "the soul, as far as we can conceive it, is nothing but a system or train of different perceptions, those of heat and cold, love and anger, thoughts and sensations; all united together, but without any perfect simplicity or identity." The thesis of Descartes that thought in general is the essence of the mind is false, since everything that exists is particular. The claim that the mind is a substance in which thoughts inhere is equally unintelligible, because we have no idea of substance, and this because we have no impression of it. All we know are "particular qualities and perceptions," such as the taste, color, size, etc. of a peach. "So our idea of any mind is only that of particular perceptions, without the notion of any thing we call substance, either simple or compound."

29. The second opinion peculiar to the author concerns geometry. He denies that extension is infinitely divisible and therefore must refute arguments from geometry (the only ones that are at all plausible) that claim that extension must be infinitely divisible. His solution is to deny that geometry is "a science exact enough to admit of conclusions so subtile as those which regard infinite divisibility." His argument is as follows. All geometrical reasoning is based on the relations of equality and inequality, and hence the reasoning is only as good as the standard for those relations. There is such an exact standard, given that quantity is composed of indivisible points. Two quantities are equal when their points stand in a one-to-one correspondence. [This is known in the literature as "Hume's Principle."] Unfortunately, this standard is useless, as we can never compute the number of points on a line. Further, it is of no use to the defenders of infinite divisibility, since it presupposes that extension consists of finitely many parts. We cannot remedy the situation by appealing to the equality of sub-segments of a line, for this begs the question or leads to a regress. If we take general appearances as the standard of proportion (thus appealing to the senses or the imagination), then there is no exactness at all. It is wished that common sense and philosophy could be reconciled on this point.

30. The second book of the Treatise concerns the passions. It is more easily understood than the first, but it has equally new and surprising conclusions. One example is given: the passions of pride and humility, with which the book begins. There are many disparate things that give rise to pride. The author finds the common circumstances in which all of these things trigger that passion. This explanation is extended to other passions, such as love and hatred. But as describing the explanations would be a lengthy venture, it will not be done.

31. One doctrine of the second book that will be of interest to the reader is that concering free-will. It is based on the treatment of cause and effect which has already been described. On the basis of that treatment, necessity is attributed to the operations of external bodies, and hence if actions of the mind can be assimilated to them, they are necessary as well. So the necessity in the operations of matter must be re-examined.

32. Neither the senses nor reason can discover a causal connection in a single instance, and we cannot discover the general principles upon which one body influences another. We are only acquainted with their constant union, and necessity is found in the determination of the mind to infer from what has commonly been united with something to that thing itself. Nothing is more evident than the constant union of particular actions with particular motives. If we are uncertain what action will take place, it is only because we do not know all the relevant causal factors. The same holds for material causes and effects.

33. There is always an inference from motives to action, and the certainty of such inference is proportional to the inferences we make about bodies. "On this is founded our belief in witnesses, our credit in history, and indeed all kinds of moral evidence, and almost the whole conduct of life."

34. This, the author holds, puts the dispute between the partisans of free will and those of necessity in a new light. Given the new understanding of what necessity is, we must conclude that human actions are necessary, as they involve constant conjunction and an inference to similiar behavior. Any "zealot" who wishes to defend free will would have to say that there is more to necessity: something that human action lacks. "But then they must show, that we have an idea of something else in the actions of matter, which, according to the foregoing reasoning, is impossible."

35. The author claims to have made new discoveries throughout the book. But the one discovery that would entitle the author to be called an "inventor" is "the use he makes of the principle of the association of ideas, which enters into most of his philosophy." The imagination can join and separate ideas so as to create all the varieties of fiction. But there is a "secret tie" which causes the mind to do this in a more regular way, as can be found even in the loosest flights of imagination. The principles are: resemblance (a picture makes one think of the person pictured), contiguity (one place makes one think of a nearby place), and causation (a son reminds one of the father who caused him to exist). It will be of "vast consequence to the philosophy of human nature if these are the only links that bind the parts of the universe together or bind us to exterior things. Things operate on our passions only through thought, and these principles tie our thoughts together. So, "they are really to us they are the cement of the universe, and all the operations of the mind must, in great measure, depend on them."