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\title{A Treatise of Human Nature\\[0.3em]\smaller{Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects}\\\vspace{1em}\smaller{[Introduction, 1.3.6, 1.3.8]}}

\author{David Hume}
\date{1739}							% Activate to display a given date or no date


\begin{document}
\maketitle

\subsection*{Introduction}

\marginnote{\smaller 1}[0cm]Nothing is more usual and more natural for those, who 
pretend to discover any thing new to the world in philosophy and the sciences, than to insinuate the praises of their 
own systems, by decrying all those, which have been advanced before them. And indeed were they content with 
lamenting that ignorance, which we still lie under in the 
most important questions, that can come before the tribunal 
of human reason, there are few, who have an acquaintance 
with the sciences, that would not readily agree with them. 
'Tis easy for one of judgment and learning, to perceive 
the weak foundation even of those systems, which have obtained the greatest credit, and have carried their pretensions 
highest to accurate and profound reasoning. Principles 
taken upon trust, consequences lamely deduced from them, 
want of coherence in the parts, and of evidence in the whole, 
these are every where to be met with in the systems of the 
most eminent philosophers, and seem to have drawn disgrace upon philosophy itself. 

\marginnote{\smaller 2}[0cm]Nor is there required such profound knowledge to discover 
the present imperfect condition of the sciences, but even the rabble without doors may judge from the noise and clamor, 
which they hear, that all goes not well within. There is 
nothing which is not the subject of debate, and in which 
men of learning are not of contrary opinions. The most 
trivial question escapes not our controversy, and in the most 
momentous we are not able to give any certain decision. 
Disputes are multiplied, as if every thing was uncertain; 
and these disputes are managed with the greatest warmth, 
as if every thing was certain. Amidst all this bustle 'tis not 
reason, which carries the prize, but eloquence; and no man 
needs ever despair of gaining proselytes to the most extravagant hypothesis, who has art enough to represent it in any 
favorable colors. The victory is not gained by the men 
at arms, who manage the pike and the sword; but by the 
trumpeters, drummers, and musicians of the army. 

\marginnote{\smaller 3}[0cm]From hence in my opinion arises that common prejudice 
against metaphysical reasonings of all kinds, even amongst 
those, who profess themselves scholars, and have a just value 
for every other part of literature. By metaphysical reasonings, they do not understand those on any particular branch 
of science, but every kind of argument, which is any way 
abstruse, and requires some attention to be comprehended. 
We have so often lost our labor in such researches, that 
we commonly reject them without hesitation, and resolve, 
if we must for ever be a prey to errors and delusions, that 
they shall at least be natural and entertaining. And indeed 
nothing but the most determined scepticism, along with a 
great degree of indolence, can justify this aversion to metaphysics. For if truth be at all within the reach of human 
capacity, 'tis certain it must lie very deep and abstruse; and 
to hope we shall arrive at it without pains, while the greatest 
geniuses have failed with the utmost pains, must certainly be esteemed sufficiently vain and presumptuous. I pretend 
to no such advantage in the philosophy I am going to unfold, and would esteem it a strong presumption against it, 
were it so very easy and obvious. 

\marginnote{\smaller 4}[0cm]'Tis evident, that all the sciences have a relation, greater 
or less, to human nature; and that however wide any of 
them may seem to run from it, they still return back by one 
passage or another. Even Mathematics, Natural Philosophy, 
and Natural Religion, are in some measure dependent on 
the science of \textsc{man}; since they lie under the cognizance 
of men, and are judged of by their powers and faculties. 
'Tis impossible to tell what changes and improvements we 
might make in these sciences were we thoroughly acquainted 
with the extent and force of human understanding, and 
could explain the nature of the ideas we employ, and of 
the operations we perform in our reasonings. And these 
improvements are the more to be hoped for in natural religion, as it is not content with instructing us in the nature 
of superior powers, but carries its views farther, to their 
disposition towards us, and our duties towards them; and 
consequently we ourselves are not only the beings, that 
reason, but also one of the objects, concerning which we 
reason. 

\marginnote{\smaller 5}[0cm]If therefore the sciences of Mathematics, Natural Philosophy, and Natural Religion, have such a dependence on 
the knowledge of man, what may be expected in the other 
sciences, whose connection with human nature is more close 
and intimate? The sole end of logic is to explain the principles and operations of our reasoning faculty, and the 
nature of our ideas: morals and criticism regard our tastes 
and sentiments: and politics consider men as united in 
society, and dependent on each other. In these four sciences of Logic, Morals, Criticism, and Politics, is comprehended 
almost everything, which it can any way import us to be 
acquainted with, or which can tend either to the improvement or ornament of the human mind. 

\marginnote{\smaller 6}[0cm]Here then is the only expedient, from which we can hope 
for success in our philosophical researches, to leave the 
tedious lingering method, which we have hitherto followed, 
and instead of taking now and then a castle or village on 
the frontier, to march up directly to the capital or center 
of these sciences, to human nature itself; which being once 
masters of, we may everywhere else hope for an easy 
victory. From this station we may extend our conquests 
over all those sciences, which more intimately concern 
human life, and may afterwards proceed at leisure to discover more fully those, which are the objects of pure curiosity. There is no question of importance, whose decision 
is not comprised in the science of man; and there is none, 
which can be decided with any certainty, before we become 
acquainted with that science. In pretending therefore to 
explain the principles of human nature, we in effect propose a complete system of the sciences, built on a foundation almost entirely new, and the only one upon which 
they can stand with any security. 

\marginnote{\smaller 7}[0cm]And as the science of man is the only solid foundation 
for the other sciences, so the only solid foundation we can 
give to this science itself must be laid on experience and 
observation. 'Tis no astonishing reflection to consider, that 
the application of experimental philosophy to moral subjects 
should come after that to natural at the distance of above 
a whole century; since we find in fact, that there was about 
the same interval betwixt the origins of these sciences; and 
that reckoning from Thales to Socrates, the space of time is nearly equal to that betwixt my Lord Bacon and some 
late philosophers in England, who have begun to put the 
science of man on a new footing, and have engaged the 
attention, and excited the curiosity of the public.\footnote{Mr. Locke, my Lord Shaftsbury, Dr. Mandeville, Mr. Hutchinson, Dr. Butler, etc.} So true 
it is, that however other nations may rival us in poetry, and 
excel us in some other agreeable arts, the improvements 
in reason and philosophy can only be owing to a land of 
toleration and of liberty. 

\marginnote{\smaller 8}[0cm]Nor ought we to think, that this latter improvement in 
the science of man will do less honor to our native country 
than the former in natural philosophy, but ought rather to 
esteem it a greater glory, upon account of the greater importance of that science, as well as the necessity it lay under 
of such a reformation. For to me it seems evident, that the 
essence of the mind being equally unknown to us with that 
of external bodies, it must be equally impossible to form 
any notion of its powers and qualities otherwise than from 
careful and exact experiments, and the observation of those 
particular effects, which result from its different circumstances and situations. And though we must endeavor to 
render all our principles as universal as possible, by tracing 
up our experiments to the utmost, and explaining all effects 
from the simplest and fewest causes, 'tis still certain we 
cannot go beyond experience; and any hypothesis, that pretends to discover the ultimate original qualities of human 
nature, ought at first to be rejected as presumptuous and 
chimerical. 

\marginnote{\smaller 9}[0cm]I do not think a philosopher, who would apply himself 
so earnestly to the explaining the ultimate principles of the 
soul, would show himself a great master in that very science of human nature, which he pretends to explain, or very 
knowing in what is naturally satisfactory to the mind of 
man. For nothing is more certain, than that despair has 
almost the same effect upon us with enjoyment, and that 
we are no sooner acquainted with the impossibility of satisfying any desire, than the desire itself vanishes. When we 
see, that we have arrived at the utmost extent of human 
reason, we sit down contented; though we be perfectly satisfied 
in the main of our ignorance, and perceive that we can give 
no reason for our most general and most refined principles, 
beside our experience of their reality; which is the reason 
of the mere vulgar, and what it required no study at first 
to have discovered for the most particular and most extraordinary phenomenon. And as this impossibility of making 
any farther progress is enough to satisfy the reader, so the 
writer may derive a more delicate satisfaction from the free 
confession of his ignorance, and from his prudence in avoiding that error, into which so many have fallen, of imposing 
their conjectures and hypotheses on the world for the most 
certain principles. When this mutual contentment and satisfaction can be obtained betwixt the master and scholar, I 
know not what more we can require of our philosophy. 

\marginnote{\smaller 10}[0cm]But if this impossibility of explaining ultimate principles 
should be esteemed a defect in the science of man, I will 
venture to affirm, that 'tis a defect common to it with all 
the sciences, and all the arts, in which we can employ ourselves, whether they be such as are cultivated in the schools 
of the philosophers, or practiced in the shops of the meanest 
artisans. None of them can go beyond experience, or establish any principles which are not founded on that authority. 
Moral philosophy has, indeed, this peculiar disadvantage, 
which is not found in natural, that in collecting its experiments, it cannot make them purposely, with premeditation, 
and after such a manner as to satisfy itself concerning every 
particular difficulty which may arise. When I am at a loss 
to know the effects of one body upon another in any situation, I need only put them in that situation, and observe 
what results from it. But should I endeavor to clear up 
after the same manner any doubt in moral philosophy, by 
placing myself in the same case with that which I consider, 
'tis evident this reflection and premeditation would so disturb 
the operation of my natural principles, as must render it 
impossible to form any just conclusion from the phenomenon. We must therefore glean up our experiments in science from a cautious observation of human life, and take 
them as they appear in the common course of the world, 
by men's behavior in company, in affairs, and in their 
pleasures. Where experiments of this kind are judiciously 
collected and compared, we may hope to establish on them 
a science, which will not be inferior in certainty, and will 
be much superior in utility to any other of human comprehension.

\subsection*{Of the Inference from the Impression to the Idea}

\marginnote{\smaller 1.3.6.1}[0cm]'Tis easy to observe, that in tracing this relation, the 
inference we draw from cause to effect, is not derived merely 
from a survey of these particular objects, and from such 
a penetration into their essences as may discover the dependence of the one upon the other. There is no object, which 
implies the existence of any other if we consider these 
objects in themselves, and never look beyond the ideas which we form of them. Such an inference would amount
to knowledge, and would imply the absolute contradiction 
and impossibility of conceiving any thing different. But 
as all distinct ideas are separable, 'tis evident there can be
no impossibility of that kind. When we pass from a present impression to the idea of any object, we might possibly have 
separated the idea from the impression, and have substituted 
any other idea in its room. 

\marginnote{\smaller 1.3.6.2}[0cm]'Tis therefore by \textsc{experience} only, that we can infer the 
existence of one object from that of another. The nature of 
experience is this. We remember to have had frequent instances of the existence of one species of objects; and also 
remember, that the individuals of another species of objects 
have always attended them, and have existed in a regular order 
of contiguity and succession with regard to them. Thus we 
remember to have seen that species of object we call \textit{flame}, 
and to have felt that species of sensation we call \textit{heat}. We 
likewise call to mind their constant conjunction in all past 
instances. Without any farther ceremony, we call the one 
\textit{cause} and the other \textit{effect}, and infer the existence of the one 
from that of the other. In all those instances, from which we 
learn the conjunction of particular causes and effects, both 
the causes and effects have been perceived by the senses, and 
are remembered: But in all cases, wherein we reason concerning them there is only one perceived or remembered, and 
the other is supplied in conformity to our past experience.

\marginnote{\smaller 1.3.6.3}[0cm]Thus in advancing we have insensibly discovered a new 
relation betwixt cause and effect, when we least expected it, 
and were entirely employed upon another subject. This relation is their \textsc{constant conjunction}. Contiguity and succession are not sufficient to make us pronounce any two objects 
to be cause and effect, unless we perceive, that these two 
relations are preserved in several instances. We may now 
see the advantage of quitting the direct survey of this relation, 
in order to discover the nature of that \textit{necessary connection}, 
which makes so essential a part of it. There are hopes, that by this means we may at last arrive at our proposed end; 
though to tell the truth, this new-discovered relation of a constant 
conjunction seems to advance us but very little in our way. For it implies no more than this, that like objects have always 
been placed in like relations of contiguity and succession; 
and it seems evident, at least at first sight, that by this means 
we can never discover any new idea, and can only multiply, 
but not enlarge the objects of our mind. It may be thought, 
that what we learn not from one object, we can never learn 
from a hundred, which are all of the same kind, and are perfectly resembling in every circumstance. As our senses 
show us in one instance two bodies, or motions, or qualities 
in certain relations of succession and contiguity; so our 
memory presents us only with a multitude of instances, 
wherein we always find like bodies, motions, or qualities in 
like relations. From the mere repetition of any past impression, even to infinity, there never will arise any new original 
idea, such as that of a necessary connection; and the number 
of impressions has in this case no more effect than if we 
confined ourselves to one only. But though this reasoning seems 
just and obvious; yet as it would be folly to despair too 
soon, we shall continue the thread of our discourse; and 
having found, that after the discovery of the constant conjunction of any objects, we always draw an inference from 
one object to another, we shall now examine the nature of 
that inference, and of the transition from the impression to 
the idea. Perhaps 'twill appear in the end, that the necessary 
connection depends on the inference, instead of the inference's 
depending on the necessary connection. 

\marginnote{\smaller 1.3.6.4}[0cm]Since it appears, that the transition from an impression 
present to the memory or senses to the idea of an object, 
which we call cause or effect, is founded on \textit{past experience}, 
and on our remembrance of their \textit{constant conjunction}, the 
next question is, whether experience produces the idea by 
means of the understanding or of the imagination; whether 
we are determined by reason to make the transition, or by a certain association and relation of perceptions. If reason determined us, it would proceed upon that principle, \textit{that instances, of which we have had no experience, must resemble those, of which we have had experience, and that the course of nature continues always uniformly the same}. In order therefore to clear up this matter, let us consider all the arguments, 
upon which such a proposition may be supposed to be founded; 
and as these must be derived either from \textit{knowledge} or \textit{probability}, let us cast our eye on each of these degrees of evidence, 
and see whether they afford any just conclusion of this nature. 

\marginnote{\smaller 1.3.6.5}[0cm]Our foregoing method of reasoning will easily convince 
us, that there can be no \textit{demonstrative} arguments to prove, 
\textit{that those instances, of which we have had no experience, 
resemble those, of which we have had experience}. We can at 
least conceive a change in the course of nature; which 
sufficiently proves, that such a change is not absolutely 
impossible. To form a clear idea of any thing, is an 
undeniable argument for its possibility, and is alone a refutation of any pretended demonstration against it. 

\marginnote{\smaller 1.3.6.6}[0cm]Probability, as it discovers not the relations of ideas, considered as such, but only those of objects, must in some 
respects be founded on the impressions of our memory and 
senses, and in some respects on our ideas. Were there no 
mixture of any impression in our probable reasonings, the 
conclusion would be entirely chimerical: And were there no 
mixture of ideas, the action of the mind, in observing the 
relation, would, properly speaking, be sensation, not reasoning. 'Tis therefore necessary, that in all probable reasonings 
there be something present to the mind, either seen or 
remembered; and that from this we infer something connected with it, which is not seen nor remembered. 

\marginnote{\smaller 1.3.6.7}[0cm]The only connection or relation of objects, which can 
lead us beyond the immediate impressions of our memory 
and senses, is that of cause and effect; and that because 'tis 
the only one, on which we can found a just inference from 
one object to another. The idea of cause and effect is derived from \textit{experience}, which informs us, that such particular objects, in all past instances, have been constantly 
conjoined with each other: And as an object similar to one of these is supposed to be immediately present in its impression, we thence presume on the existence of one similar 
to its usual attendant. According to this account of things, 
which is, I think, in every point unquestionable, probability 
is founded on the presumption of a resemblance betwixt 
those objects, of which we have had experience, and those, 
of which we have had none; and therefore 'tis impossible 
this presumption can arise from probability. The same principle cannot be both the cause and effect of another; and 
this is, perhaps, the only proposition concerning that relation, 
which is either intuitively or demonstratively certain, 

\marginnote{\smaller 1.3.6.8}[0cm]Should any one think to elude this argument; and without determining whether our reasoning on this subject be 
derived from demonstration or probability, pretend that all 
conclusions from causes and effects are built on solid 
reasoning: I can only desire, that this reasoning may be 
produced, in order to be exposed to our examination. It 
may, perhaps, be said, that after experience of the constant 
conjunction of certain objects, we reason in the following 
manner. Such an object is always found to produce another. 
'Tis impossible it could have this effect, if it was not endowed 
with a power of production. The power necessarily implies 
the effect; and therefore there is a just foundation for 
drawing a conclusion from the existence of one object to 
that of its usual attendant. The past production implies 
a power: The power implies a new production: And the 
new production is what we infer from the power and the past 
production. 

\marginnote{\smaller 1.3.6.9}[0cm]'Twere easy for me to show the weakness of this reasoning, 
were I willing to make use of those observations I have 
already made, that the idea of \textit{production} is the same with 
that of \textit{causation}, and that no existence certainly and demonstratively implies a power in any other object; or were it proper to anticipate what I shall have occasion to remark afterwards concerning the idea we form of \textit{power} and \textit{efficacy}. 
But as such a method of proceeding may seem either to 
weaken my system, by resting one part of it on another, or to breed a confusion in my reasoning, I shall endeavor 
to maintain my present assertion without any such assistance. 

\marginnote{\smaller 1.3.6.10}[0cm]It shall therefore be allowed for a moment, that the production of one object by another in any one instance implies 
a power; and that this power is connected with its effect. 
But it having been already proved, that the power lies not 
in the sensible qualities of the cause; and there being 
nothing but the sensible qualities present to us; I ask, why 
in other instances you presume that the same power still 
exists, merely upon the appearance of these qualities? Your 
appeal to past experience decides nothing in the present 
case; and at the utmost can only prove, that that very object, 
which produced any other, was at that very instant endowed 
with such a power; but can never prove, that the same 
power must continue in the same object or collection of 
sensible qualities; much less, that a like power is always 
conjoined with like sensible qualities. Should it be said, 
that we have experience, that the same power continues 
united with the same object, and that like objects are 
endowed with like powers, I would renew my question, \textit{why 
from this experience we form any conclusion beyond those past 
instances, of which we have had experience}. If you answer 
this question in the same manner as the preceding, your 
answer gives still occasion to a new question of the same 
kind, even \textit{in infinitum} [to infinity]; which clearly proves, that the foregoing reasoning had no just foundation. 

\marginnote{\smaller 1.3.6.11}[0cm]Thus not only our reason fails us in the discovery of the 
\textit{ultimate connection} of causes and effects, but even after experience has informed us of their \textit{constant conjunction}, 'tis 
impossible for us to satisfy ourselves by our reason, why we 
should extend that experience beyond those particular instances, which have fallen under our observation. We suppose, but are never able to prove, that there must be 
a resemblance betwixt those objects, of which we have had experience, and those which lie beyond the reach of our discovery. 

\marginnote{\smaller 1.3.6.12}[0cm]We have already taken notice of certain relations, which 
make us pass from one object to another, even though there be 
no reason to determine us to that transition; and this we 
may establish for a general rule, that wherever the mind 
constantly and uniformly makes a transition without any 
reason, it is influenced by these relations. Now this is 
exactly the present case. Reason can never show us the 
connection of one object with another, though aided by experience, and the observation of their constant conjunction 
in all past instances. When the mind, therefore, passes from 
the idea or impression of one object to the idea or belief of 
another, it is not determined by reason, but by certain 
principles, which associate together the ideas of these objects, 
and unite them in the imagination. Had ideas no more 
union in the fancy than objects seem to have to the understanding, we could never draw any inference from causes 
to effects, nor repose belief in any matter of fact. The 
inference, therefore, depends solely on the union of ideas. 

\marginnote{\smaller 1.3.6.13}[0cm]The principles of union among ideas I have reduced to 
three general ones, and have asserted, that the idea or 
impression of any object naturally introduces the idea of any 
other object, that is resembling, contiguous to, or connected 
with it. These principles I allow to be neither the \textit{infallible} 
nor the \textit{sole} causes of a union among ideas. They are not 
the infallible causes. For one may fix his attention during 
some time on any one object without looking farther. They 
are not the sole causes. For the thought has evidently a 
very irregular motion in running along its objects, and may 
leap from the heavens to the earth, from one end of the 
creation to the other, without any certain method or order. 
But though I allow this weakness in these three relations, and this irregularity in the imagination; yet I assert that the only \textit{general} principles, which associate ideas, are resemblance, contiguity and causation. 

\marginnote{\smaller 1.3.6.14}[0cm]There is indeed a principle of union among ideas, which 
at first sight may be esteemed different from any of these, but will be found at the bottom to depend on the same 
origin. When every individual of any species of objects is 
found by experience to be constantly united with an individual of another species, the appearance of any new 
individual of either species naturally conveys the thought to 
its usual attendant. Thus because such a particular idea 
is commonly annexed to such a particular word, nothing is 
required but the hearing of that word to produce the correspondent idea; and 'twill scarce be possible for the mind, by 
its utmost efforts, to prevent that transition. In this case it 
is not absolutely necessary, that upon hearing such a particular sound, we should reflect on any past experience, and 
consider what idea has been usually connected with the 
sound. The imagination of itself supplies the place of this 
reflection, and is so accustomed to pass from the word to 
the idea, that it interposes not a moment's delay betwixt the 
hearing of the one, and the conception of the other. 

\marginnote{\smaller 1.3.6.15}[0cm]But though I acknowledge this to be a true principle of 
association among ideas, I assert it to be the very same with 
that betwixt the ideas of cause and effect, and to be an 
essential part in all our reasonings from that relation. We 
have no other notion of cause and effect, but that of certain 
objects, which have been \textit{always conjoined} together, and 
which in all past instances have been found inseparable. 
We cannot penetrate into the reason of the conjunction. 
We only observe the thing itself, and always find that from 
the constant conjunction the objects acquire an union in the 
imagination. When the impression of one becomes present 
to us, we immediately form an idea of its usual attendant; 
and consequently we may establish this as one part of the 
definition of an opinion or belief, that 'tis \textit{an idea related to 
or associated with a present impression}. 

\marginnote{\smaller 1.3.6.16}[0cm]Thus though causation be a \textit{philosophical} relation, as implying contiguity, succession, and constant conjunction, yet 
'tis only so far as it is a \textit{natural} relation, and produces a union among our ideas, that we are able to reason upon it, 
or draw any inference from it.\pagebreak

\subsection*{Of the Causes of Belief}

\noindent[\thinspace\ldots]\\

\marginnote{\smaller 1.3.8.8}[0cm]In order to put this whole affair in a fuller light, let us consider it as a question in natural philosophy, which we must 
determine by experience and observation. I suppose there is an object presented, from which I draw a certain conclusion, and form to myself ideas, which I am said to believe or assent to. Here 'tis evident, that however that object, which is present to my senses, and that other, whose existence I infer by reasoning, may be thought to influence each other by their particular powers or qualities; yet as the phenomenon of belief, which we at present examine, is merely internal, these powers and qualities, being entirely unknown, can have no hand in producing it. 'Tis the present impression, which is to be considered as the true and real cause of the idea, and of the belief which attends it. We must therefore endeavour to discover by experiments the particular qualities, by which 'tis enabled to produce so extraordinary an effect.

\marginnote{\smaller 1.3.8.9}[0cm]First then I observe, that the present impression has not 
this effect by its own proper power and efficacy, and when 
considered alone, as a single perception, limited to the present moment. I find, that an impression, from which, on its 
first appearance, I can draw no conclusion, may afterwards 
become the foundation of belief, when I have had experience 
of its usual consequences. We must in every case have 
observed the same impression in past instances, and have 
found it to be constantly conjoined with some other impression. This is confirmed by such a multitude of experiments, 
that it admits not of the smallest doubt. 

\marginnote{\smaller 1.3.8.10}[0cm]From a second observation I conclude, that the belief, 
which attends the present impression, and is produced by a 
number of past impressions and conjunctions; that this 
belief, I say, arises immediately, without any new operation 
of the reason or imagination. Of this I can be certain, 
because I never am conscious of any such operation, and 
find nothing in the subject, on which it can be founded. 
Now as we call every thing \textsc{custom}, which proceeds from 
a past repetition, without any new reasoning or conclusion, 
we may establish it as a certain truth, that all the belief, 
which follows upon any present impression, is derived solely 
from that origin. When we are accustomed to see two impressions conjoined together, the appearance or idea of the one immediately carries us to the idea of the other. 

\marginnote{\smaller 1.3.8.11}[0cm]Being fully satisfied on this head, I make a third set of experiments, in order to know, whether any thing be requisite, beside the customary transition, towards the production of this phenomenon of belief. I therefore change the first 
impression into an idea; and observe, that though the customary 
transition to the correlative idea still remains, yet there is in 
reality no belief nor persuasion. A present impression, then, 
is absolutely requisite to this whole operation; and when after 
this I compare an impression with an idea, and find that 
their only difference consists in their different degrees of 
force and vivacity, I conclude upon the whole, that belief is 
a more vivid and intense conception of an idea, proceeding 
from its relation to a present impression. 

\marginnote{\smaller 1.3.8.12}[0cm]Thus all probable reasoning is nothing but a species of 
sensation. 'Tis not solely in poetry and music, we must 
follow our taste and sentiment, but likewise in philosophy. 
When I am convinced of any principle, 'tis only an idea, 
which strikes more strongly upon me. When I give the preference to one set of arguments above another, I do nothing 
but decide from my feeling concerning the superiority of their 
influence. Objects have no discoverable connection together; 
nor is it from any other principle but custom operating upon 
the imagination, that we can draw any inference from the 
appearance of one to the existence of another. 

\marginnote{\smaller 1.3.8.13}[0cm]'Twill here be worth our observation, that the past experience, on which all our judgments concerning cause and 
effect depend, may operate on our mind in such an insensible 
manner as never to be taken notice of, and may even in some 
measure be unknown to us. A person, who stops short in 
his journey upon meeting a river in his way, foresees the consequences of his proceeding forward; and his knowledge of 
these consequences is conveyed to him by past experience, 
which informs him of such certain conjunctions of causes and 
effects. But can we think, that on this occasion he reflects on any past experience, and calls to remembrance instances, 
that he has seen or heard of, in order to discover the effects 
of water on animal bodies? No surely; this is not the method in which he proceeds in his reasoning. The idea of sinking is so closely connected with that of water, and the idea of 
suffocating with that of sinking, that the mind makes the 
transition without the assistance of the memory. The 
custom operates before we have time for reflection. The 
objects seem so inseparable, that we interpose not a moment's 
delay in passing from the one to the other. But as this 
transition proceeds from experience, and not from any 
primary connection betwixt the ideas, we must necessarily 
acknowledge, that experience may produce a belief and a 
judgment of causes and effects by a secret operation, and 
without being once thought of. This removes all pretext, if 
there yet remains any, for asserting that the mind is convinced 
by reasoning of that principle, that instances of which we have 
no experience must necessarily resemble those of which we have. 
For we here find, that the understanding or imagination can 
draw inferences from past experience, without reflecting on 
it; much more without forming any principle concerning it, 
or reasoning upon that principle.

\marginnote{\smaller 1.3.8.14}[0cm]In general we may observe, that in all the most established 
and uniform conjunctions of causes and effects, such as those 
of gravity, impulse, solidity, etc. the mind never carries its 
view expressly to consider any past experience; though in 
other associations of objects, which are more rare and unusual, 
it may assist the custom and transition of ideas by this 
reflection. Nay we find in some cases, that the reflection 
produces the belief without the custom; or more properly 
speaking, that the reflection produces the custom in an 
oblique and artificial manner. I explain myself. 'Tis certain, 
that not only in philosophy, but even in common life, we 
may attain the knowledge of a particular cause merely by one 
experiment, provided it be made with judgment, and after a 
careful removal of all foreign and superfluous circumstances. Now as after one experiment of this kind, the mind, upon the appearance either of the cause or the effect, can draw an inference concerning the existence of its correlative; and as a habit can never be acquired merely by one instance; it may be thought, that belief cannot in this case be esteemed the 
effect of custom. But this difficulty will vanish, if we consider, that though we are here supposed to have had only one 
experiment of a particular effect, yet we have many millions 
to convince us of this principle; \textit{that like objects, placed in like 
circumstances, will always produce like effects}; and as this 
principle has established itself by a sufficient custom, it 
bestows an evidence and firmness on any opinion, to which 
it can be applied. The connection of the ideas is not 
habitual after one experiment; but this connection is comprehended under another principle, that is habitual; which 
brings us back to our hypothesis. In all cases we transfer 
our experience to instances, of which we have no experience, 
either \textit{expressly} or \textit{tacitly}, either \textit{directly} or \textit{indirectly}.\\

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Original text from the \href{https://archive.org/details/treatiseofhumann002393mbp/page/n5/mode/2up}{Internet Archive}; modernized by \href{http://www.trevorpearce.com/}{Trevor Pearce}.


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