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\title{Sceptical Doubts Concerning the Operation of the Understanding and their Sceptical Solution\footnote{These are Sections 4--5 of Hume's \textit{An Enquiry Concerning Human Understanding} (1748); original text from \href{http://www.gutenberg.org/cache/epub/9662/pg9662.txt}{Project Gutenburg}; modernized text by \href{http://www.trevorpearce.com/}{Trevor Pearce}.}}
\author{David Hume}
\date{1748}							% Activate to display a given date or no date


\begin{document}
\maketitle

\subsection*{Sceptical Doubts}

\subsubsection*{Part 1}

\marginnote{\smaller4.1}[0cm]All the objects of human reason or enquiry may naturally be divided
into two kinds, \textit{viz}., \textit{relations of ideas}, and \textit{matters of fact}. Of
the first kind are the sciences of geometry, algebra, and arithmetic;
and in short, every affirmation which is either intuitively or
demonstratively certain. \textit{That the square of the hypothenuse is equal to
the square of the two sides}, is a proposition which expresses a
relation between these figures. \textit{That three times five is equal to the
half of thirty}, expresses a relation between these numbers.
Propositions of this kind are discoverable by the mere operation of
thought, without dependence on what is anywhere existent in the
universe. Though there never were a circle or triangle in nature, the
truths demonstrated by Euclid would for ever retain their certainty
and evidence.

\marginnote{\smaller4.2}[0cm]Matters of fact, which are the second objects of human reason, are
not ascertained in the same manner; nor is our evidence of their truth,
however great, of a like nature with the foregoing. 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. \textit{That the sun will
not rise tomorrow} is no less intelligible a proposition, and implies
no more contradiction than the affirmation, \textit{that it will rise}. We
should in vain, therefore, attempt to demonstrate its falsehood. Were it
demonstratively false, it would imply a contradiction, and could never
be distinctly conceived by the mind.

\marginnote{\smaller4.3}[0cm]It may, therefore, be a subject worthy of curiosity, to enquire what 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. This part of philosophy, it is observable, has
been little cultivated, either by the ancients or moderns; and therefore
our doubts and errors, in the prosecution of so important an enquiry,
may be the more excusable; while we march through such difficult paths
without any guide or direction. They may even prove useful, by exciting
curiosity, and destroying that implicit faith and security, which is the
bane of all reasoning and free enquiry. The discovery of defects in the
common philosophy, if any such there be, will not, I presume, be a
discouragement, but rather an incitement, as is usual, to attempt
something more full and satisfactory than has yet been proposed to
the public.

\marginnote{\smaller4.4}[0cm]All reasonings concerning matter of fact seem to be founded on the
relation of \textit{cause} and \textit{effect}. By means of that relation alone we can
go beyond the evidence of our memory and senses. If you were to ask a
man, why he believes any matter of fact, which is absent; for instance,
that his friend is in the country, or in France; he would give you a
reason; and this reason would be some other fact; as a letter received
from him, or the knowledge of his former resolutions and promises. A man
finding a watch or any other machine in a desert island, would conclude
that there had once been men in that island. All our reasonings
concerning fact are of the same nature. And here it is constantly
supposed that there is a connection between the present fact and that
which is inferred from it. Were there nothing to bind them together, the
inference would be entirely precarious. The hearing of an articulate
voice and rational discourse in the dark assures us of the presence of
some person: Why? because these are the effects of the human make and
fabric, and closely connected with it. If we anatomize all the other
reasonings of this nature, we shall find that they are founded on the
relation of cause and effect, and that this relation is either near or
remote, direct or collateral. Heat and light are collateral effects of
fire, and the one effect may justly be inferred from the other.

\marginnote{\smaller4.5}[0cm]If we would satisfy ourselves, therefore, concerning the nature of
that evidence, which assures us of matters of fact, we must enquire how
we arrive at the knowledge of cause and effect.

\marginnote{\smaller4.6}[0cm]I shall venture to affirm, as a general proposition, which admits of no
exception, that the knowledge of this relation is not, in any instance,
attained by reasonings \textit{a priori}; but arises entirely from experience,
when we find that any particular objects are constantly conjoined with
each other. Let an object be presented to a man of ever so strong
natural reason and abilities; if that object be entirely new to him, he
will not be able, by the most accurate examination of its sensible
qualities, to discover any of its causes or effects. \textit{Adam}, though his
rational faculties be supposed, at the very first, entirely perfect,
could not have inferred from the fluidity and transparency of water that
it would suffocate him, or from the light and warmth of fire that it
would consume him. No object ever discovers, by the qualities which
appear to the senses, either the causes which produced it, or the
effects which will arise from it; nor can our reason, unassisted by
experience, ever draw any inference concerning real existence and
matter of fact.

\marginnote{\smaller4.7}[0cm]This proposition, \textit{that causes and effects are discoverable, not by
reason but by experience}, will readily be admitted with regard to such
objects, as we remember to have once been altogether unknown to us;
since we must be conscious of the utter inability, which we then lay
under, of foretelling what would arise from them. Present two smooth
pieces of marble to a man who has no tincture of natural philosophy; he
will never discover that they will adhere together in such a manner as
to require great force to separate them in a direct line, while they
make so small a resistance to a lateral pressure. Such events, as bear
little analogy to the common course of nature, are also readily
confessed to be known only by experience; nor does any man imagine that
the explosion of gunpowder, or the attraction of a loadstone, could ever
be discovered by arguments \textit{a priori}. In like manner, when an effect is
supposed to depend upon an intricate machinery or secret structure of
parts, we make no difficulty in attributing all our knowledge of it to
experience. Who will assert that he can give the ultimate reason, why
milk or bread is proper nourishment for a man, not for a lion or
a tiger?

\marginnote{\smaller4.8}[0cm]But the same truth may not appear, at first sight, to have the same
evidence with regard to events, which have become familiar to us from
our first appearance in the world, which bear a close analogy to the
whole course of nature, and which are supposed to depend on the simple
qualities of objects, without any secret structure of parts. We are apt
to imagine that we could discover these effects by the mere operation of
our reason, without experience. We fancy, that were we brought on a
sudden into this world, we could at first have inferred that one
billiard-ball would communicate motion to another upon impulse; and that
we needed not to have waited for the event, in order to pronounce with
certainty concerning it. Such is the influence of custom, that, where it
is strongest, it not only covers our natural ignorance, but even
conceals itself, and seems not to take place, merely because it is found
in the highest degree.

\marginnote{\smaller4.9}[0cm]But to convince us that all the laws of nature, and all the
operations of bodies without exception, are known only by experience,
the following reflections may, perhaps, suffice. Were any object
presented to us, and were we required to pronounce concerning the
effect, which will result from it, without consulting past observation;
after what manner, I beseech you, must the mind proceed in this
operation? It must invent or imagine some event, which it ascribes to
the object as its effect; and it is plain that this invention must be
entirely arbitrary. The mind can never possibly find the effect in the
supposed cause, by the most accurate scrutiny and examination. For the
effect is totally different from the cause, and consequently can never
be discovered in it. Motion in the second billiard-ball is a quite
distinct event from motion in the first; nor is there anything in the
one to suggest the smallest hint of the other. A stone or piece of metal
raised into the air, and left without any support, immediately falls:
but to consider the matter \textit{a priori}, is there anything we discover in
this situation which can beget the idea of a downward, rather than an
upward, or any other motion, in the stone or metal?

\marginnote{\smaller4.10}[0cm]And as the first
imagination or invention of a particular effect, in all natural
operations, is arbitrary, where we consult not experience; so must we
also esteem the supposed tie or connection between the cause and effect,
which binds them together, and renders it impossible that any other
effect could result from the operation of that cause. When I see, for
instance, a billiard-ball moving in a straight line towards another;
even suppose motion in the second ball should by accident be suggested
to me, as the result of their contact or impulse; may I not conceive,
that a hundred different events might as well follow from that cause?
May not both these balls remain at absolute rest? May not the first ball
return in a straight line, or leap off from the second in any line or
direction? All these suppositions are consistent and conceivable. Why
then should we give the preference to one, which is no more consistent
or conceivable than the rest? All our reasonings \textit{a priori} will never
be able to show us any foundation for this preference.

\marginnote{\smaller4.11}[0cm]In a word, then, 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, \textit{a priori}, must be entirely arbitrary.
And even after it is suggested, the conjunction of it with the cause
must appear equally arbitrary; since there are always many other
effects, which, to reason, must seem fully as consistent and natural. In
vain, therefore, should we pretend to determine any single event, or
infer any cause or effect, without the assistance of observation and
experience.

\marginnote{\smaller4.12}[0cm]Hence we may discover the reason why no philosopher, who is rational
and modest, has ever pretended to assign the ultimate cause of any
natural operation, or to show distinctly the action of that power, which
produces any single effect in the universe. It is confessed, that the
utmost effort of human reason is to reduce the principles, productive of
natural phenomena, to a greater simplicity, and to resolve the many
particular effects into a few general causes, by means of reasonings
from analogy, experience, and observation. But as to the causes of these
general causes, we should in vain attempt their discovery; nor shall we
ever be able to satisfy ourselves, by any particular explication of
them. These ultimate springs and principles are totally shut up from
human curiosity and enquiry. Elasticity, gravity, cohesion of parts,
communication of motion by impulse; these are probably the ultimate
causes and principles which we shall ever discover in nature; and we may
esteem ourselves sufficiently happy, if, by accurate enquiry and
reasoning, we can trace up the particular phenomena to, or near to,
these general principles. The most perfect philosophy of the natural
kind only staves off our ignorance a little longer: as perhaps the most
perfect philosophy of the moral or metaphysical kind serves only to
discover larger portions of it. Thus the observation of human blindness
and weakness is the result of all philosophy, and meets us at every
turn, in spite of our endeavors to elude or avoid it.

\marginnote{\smaller4.13}[0cm]Nor is geometry, when taken into the assistance of natural
philosophy, ever able to remedy this defect, or lead us into the
knowledge of ultimate causes, by all that accuracy of reasoning for
which it is so justly celebrated. Every part of mixed mathematics
proceeds upon the supposition that certain laws are established by
nature in her operations; and abstract reasonings are employed, either
to assist experience in the discovery of these laws, or to determine
their influence in particular instances, where it depends upon any
precise degree of distance and quantity. Thus, it is a law of motion,
discovered by experience, that the moment or force of any body in motion
is in the compound ratio or proportion of its solid contents and its
velocity; and consequently, that a small force may remove the greatest
obstacle or raise the greatest weight, if, by any contrivance or
machinery, we can increase the velocity of that force, so as to make it
an overmatch for its antagonist. Geometry assists us in the application
of this law, by giving us the just dimensions of all the parts and
figures which can enter into any species of machine; but still the
discovery of the law itself is owing merely to experience, and all the
abstract reasonings in the world could never lead us one step towards
the knowledge of it. When we reason \textit{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 connection between them. A man must be very sagacious who
could discover by reasoning that crystal is the effect of heat, and ice
of cold, without being previously acquainted with the operation of these
qualities.\pagebreak

\subsubsection*{Part 2}

\marginnote{\smaller4.14}[0cm]But we have not yet attained any tolerable satisfaction with regard
to the question first proposed. Each solution still gives rise to a new
question as difficult as the foregoing, and leads us on to farther
enquiries. When it is asked, \textit{What is the nature of all our reasonings
concerning matter of fact?} the proper answer seems to be, that they are
founded on the relation of cause and effect. When again it is asked,
\textit{What is the foundation of all our reasonings and conclusions concerning
that relation?} it may be replied in one word, \textbf{experience}. But if we
still carry on our sifting humor, and ask, \textit{What is the foundation of
all conclusions from experience?} this implies a new question, which may
be of more difficult solution and explication. Philosophers, that give
themselves airs of superior wisdom and sufficiency, have a hard task
when they encounter persons of inquisitive dispositions, who push them
from every corner to which they retreat, and who are sure at last to
bring them to some dangerous dilemma. The best expedient to prevent this
confusion, is to be modest in our pretensions; and even to discover the
difficulty ourselves before it is objected to us. By this means, we may
make a kind of merit of our very ignorance.

\marginnote{\smaller4.15}[0cm]I shall content myself, in this section, with an easy task, and shall
pretend only to give a negative answer to the question here proposed. I
say then, that, even after we have experience of the operations of cause
and effect, our conclusions from that experience are \textit{not} founded on
reasoning, or any process of the understanding. This answer we must
endeavor both to explain and to defend.

\marginnote{\smaller4.16}[0cm]It must certainly be allowed, that nature has kept us at a great
distance from all her secrets, and has afforded us only the knowledge of
a few superficial qualities of objects; while she conceals from us those
powers\footnote{The word, power, is here used in a loose and popular sense. The more accurate explication of it would give additional evidence to the argument. See Section 7.} and principles on which the influence of those objects entirely
depends. Our senses inform us of the color, weight, and consistence of
bread; but neither sense nor reason can ever inform us of those
qualities which fit it for the nourishment and support of a human body.
Sight or feeling conveys an idea of the actual motion of bodies; but as
to that wonderful force or power, which would carry on a moving body for
ever in a continued change of place, and which bodies never lose but by
communicating it to others; of this we cannot form the most distant
conception. But notwithstanding this ignorance of natural powers[6] and
principles, we always presume, when we see like sensible qualities, that
they have like secret powers, and expect that effects, similar to those
which we have experienced, will follow from them. If a body of like
color and consistence with that bread, which we have formerly eat, be
presented to us, we make no scruple of repeating the experiment, and
foresee, with certainty, like nourishment and support. Now this is a
process of the mind or thought, of which I would willingly know the
foundation. It is allowed on all hands that there is no known connection
between the sensible qualities and the secret powers; and consequently,
that the mind is not led to form such a conclusion concerning their
constant and regular conjunction, by anything which it knows of their
nature. As to past \textit{experience}, it can be allowed to give \textit{direct} and
\textit{certain} information of those precise objects only, and that precise
period of time, which fell under its cognizance: but why this experience
should be extended to future times, and to other objects, which for
aught we know, may be only in appearance similar; this is the main
question on which I would insist. The bread, which I formerly eat,
nourished me; that is, a body of such sensible qualities was, at that
time, endued with such secret powers: but does it follow, that other
bread must also nourish me at another time, and that like sensible
qualities must always be attended with like secret powers? The
consequence seems nowise necessary. At least, it must be acknowledged
that there is here a consequence drawn by the mind; that there is a
certain step taken; a process of thought, and an inference, which wants
to be explained. These two propositions are far from being the same, \textit{I
have found that such an object has always been attended with such an
effect}, and \textit{I foresee, that other objects, which are, in appearance,
similar, will be attended with similar effects}. I shall allow, if you
please, that the one proposition may justly be inferred from the other:
I know, in fact, that it always is inferred. But if you insist that the
inference is made by a chain of reasoning, I desire you to produce that
reasoning. The connection between these propositions is not intuitive.
There is required a medium, which may enable the mind to draw such an
inference, if indeed it be drawn by reasoning and argument. What that
medium is, I must confess, passes my comprehension; and it is incumbent
on those to produce it, who assert that it really exists, and is the
origin of all our conclusions concerning matter of fact.

\marginnote{\smaller4.17}[0cm]This negative argument must certainly, in process of time, become
altogether convincing, if many penetrating and able philosophers shall
turn their enquiries this way and no one be ever able to discover any
connecting proposition or intermediate step, which supports the
understanding in this conclusion. But as the question is yet new, every
reader may not trust so far to his own penetration, as to conclude,
because an argument escapes his enquiry, that therefore it does not
really exist. For this reason it may be requisite to venture upon a more
difficult task; and enumerating all the branches of human knowledge,
endeavor to show that none of them can afford such an argument.

\marginnote{\smaller4.18}[0cm]All reasonings may be divided into two kinds, namely, demonstrative
reasoning, or that concerning relations of ideas, and moral reasoning,
or that concerning matter of fact and existence. That there are no
demonstrative arguments in the case seems evident; since it implies no
contradiction that the course of nature may change, and that an object,
seemingly like those which we have experienced, may be attended with
different or contrary effects. May I not clearly and distinctly conceive
that a body, falling from the clouds, and which, in all other respects,
resembles snow, has yet the taste of salt or feeling of fire? Is there
any more intelligible proposition than to affirm, that all the trees
will flourish in December and January, and decay in May and June? Now
whatever is intelligible, and can be distinctly conceived, implies no
contradiction, and can never be proved false by any demonstrative
argument or abstract reasoning \textit{a priori}.

\marginnote{\smaller4.19}[0cm]If we be, therefore, engaged by arguments to put trust in past
experience, and make it the standard of our future judgement, these
arguments must be probable only, or such as regard matter of fact and
real existence, according to the division above mentioned. But that
there is no argument of this kind, must appear, if our explication of
that species of reasoning be admitted as solid and satisfactory. 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 endeavor, 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.

\marginnote{\smaller4.20}[0cm]In reality, all arguments from experience are founded on the
similarity which we discover among natural objects, and by which we are
induced to expect effects similar to those which we have found to follow
from such objects. And though none but a fool or madman will ever
pretend to dispute the authority of experience, or to reject that great
guide of human life, it may surely be allowed a philosopher to have so
much curiosity at least as to examine the principle of human nature,
which gives this mighty authority to experience, and makes us draw
advantage from that similarity which nature has placed among different
objects. From causes which appear \textit{similar} we expect similar effects.
This is the sum of all our experimental conclusions. Now it seems
evident that, if this conclusion were formed by reason, it would be as
perfect at first, and upon one instance, as after ever so long a course
of experience. But the case is far otherwise. Nothing so like as eggs;
yet no one, on account of this appearing similarity, expects the same
taste and relish in all of them. It is only after a long course of
uniform experiments in any kind, that we attain a firm reliance and
security with regard to a particular event. Now where is that process of
reasoning which, from one instance, draws a conclusion, so different
from that which it infers from a hundred instances that are nowise
different from that single one? This question I propose as much for the
sake of information, as with an intention of raising difficulties. I
cannot find, I cannot imagine any such reasoning. But I keep my mind
still open to instruction, if any one will vouchsafe to bestow it on me.

\marginnote{\smaller4.21}[0cm]Should it be said that, from a number of uniform experiments, we
\textit{infer} a connection between the sensible qualities and the secret
powers; this, I must confess, seems the same difficulty, couched in
different terms. The question still recurs, on what process of argument
this \textit{inference} is founded? Where is the medium, the interposing ideas,
which join propositions so very wide of each other? It is confessed that
the color, consistence, and other sensible qualities of bread appear
not, of themselves, to have any connection with the secret powers of
nourishment and support. For otherwise we could infer these secret
powers from the first appearance of these sensible qualities, without
the aid of experience; contrary to the sentiment of all philosophers,
and contrary to plain matter of fact. Here, then, is our natural state
of ignorance with regard to the powers and influence of all objects. How
is this remedied by experience? It only shows us a number of uniform
effects, resulting from certain objects, and teaches us that those
particular objects, at that particular time, were endowed with such
powers and forces. When a new object, endowed with similar sensible
qualities, is produced, we expect similar powers and forces, and look
for a like effect. From a body of like color and consistence with bread
we expect like nourishment and support. But this surely is a step or
progress of the mind, which wants to be explained. When a man says, \textit{I
have found, in all past instances, such sensible qualities conjoined
with such secret powers}: And when he says, \textit{Similar sensible qualities
will always be conjoined with similar secret powers}, he is not guilty
of a tautology, nor are these propositions in any respect the same. You
say that the one proposition is an inference from the other. But you
must confess that the inference is not intuitive; neither is it
demonstrative: Of what nature is it, then? To say it is experimental, is
begging the question. For all inferences from experience suppose, as
their foundation, that the future will resemble the past, and that
similar powers will be conjoined with similar sensible qualities. If
there be any suspicion that the course of nature may change, and that
the past may be no rule for the future, all experience becomes useless,
and can give rise to no inference or conclusion. It is impossible,
therefore, that any arguments from experience can prove this resemblance
of the past to the future; since all these arguments are founded on the
supposition of that resemblance. Let the course of things be allowed
hitherto ever so regular; that alone, without some new argument or
inference, proves not that, for the future, it will continue so. 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? What logic, what process
of argument secures you against this supposition? My practice, you say,
refutes my doubts. But you mistake the purport of my question. As an
agent, I am quite satisfied in the point; but as a philosopher, who has
some share of curiosity, I will not say scepticism, I want to learn the
foundation of this inference. No reading, no enquiry has yet been able
to remove my difficulty, or give me satisfaction in a matter of such
importance. Can I do better than propose the difficulty to the public,
even though, perhaps, I have small hopes of obtaining a solution? We
shall at least, by this means, be sensible of our ignorance, if we do
not augment our knowledge.

\marginnote{\smaller4.22}[0cm]I must confess that a man is guilty of unpardonable arrogance who
concludes, because an argument has escaped his own investigation, that
therefore it does not really exist. I must also confess that, though all
the learned, for several ages, should have employed themselves in
fruitless search upon any subject, it may still, perhaps, be rash to
conclude positively that the subject must, therefore, pass all human
comprehension. Even though we examine all the sources of our knowledge,
and conclude them unfit for such a subject, there may still remain a
suspicion, that the enumeration is not complete, or the examination not
accurate. But with regard to the present subject, there are some
considerations which seem to remove all this accusation of arrogance or
suspicion of mistake.

\marginnote{\smaller4.23}[0cm]It is certain that the most ignorant and stupid peasants, nay infants,
nay even brute beasts, improve by experience, and learn the qualities of
natural objects, by observing the effects which result from them. When a
child has felt the sensation of pain from touching the flame of a
candle, he will be careful not to put his hand near any candle; but will
expect a similar effect from a cause which is similar in its sensible
qualities and appearance. If you assert, therefore, that the
understanding of the child is led into this conclusion by any process of
argument or ratiocination, I may justly require you to produce that
argument; nor have you any pretense to refuse so equitable a demand. You
cannot say that the argument is abstruse, and may possibly escape your
enquiry; since you confess that it is obvious to the capacity of a mere
infant. If you hesitate, therefore, a moment, or if, after reflection,
you produce any intricate or profound argument, you, in a manner, give
up the question, and confess that it 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. This is the proposition
which I intended to enforce in the present section. If I be right, I
pretend not to have made any mighty discovery. And if I be wrong, I must
acknowledge myself to be indeed a very backward scholar; since I cannot
now discover an argument which, it seems, was perfectly familiar to me
long before I was out of my cradle.

\subsection*{Sceptical Solution of These Doubts}

\subsubsection*{Part 1}

\marginnote{\smaller5.1}[0cm]The passion for philosophy, like that for religion, seems liable to
this inconvenience, that, though it aims at the correction of our
manners, and extirpation of our vices, it may only serve, by imprudent
management, to foster a predominant inclination, and push the mind, with
more determined resolution, towards that side which already \textit{draws} too
much, by the bias and propensity of the natural temper. It is certain
that, while we aspire to the magnanimous firmness of the philosophic
sage, and endeavor to confine our pleasures altogether within our own
minds, we may, at last, render our philosophy like that of Epictetus,
and other \textit{Stoics}, only a more refined system of selfishness, and
reason ourselves out of all virtue as well as social enjoyment. While we
study with attention the vanity of human life, and turn all our thoughts
towards the empty and transitory nature of riches and honors, we are,
perhaps, all the while flattering our natural indolence, which, hating
the bustle of the world, and drudgery of business, seeks a pretense of
reason to give itself a full and uncontrolled indulgence. There is,
however, one species of philosophy which seems little liable to this
inconvenience, and that because it strikes in with no disorderly passion
of the human mind, nor can mingle itself with any natural affection or
propensity; and that is the \textbf{academic} or \textbf{sceptical} philosophy. The
academics always talk of doubt and suspense of judgement, of danger in
hasty determinations, of confining to very narrow bounds the enquiries
of the understanding, and of renouncing all speculations which lie not
within the limits of common life and practice. Nothing, therefore, can
be more contrary than such a philosophy to the supine indolence of the
mind, its rash arrogance, its lofty pretensions, and its superstitious
credulity. Every passion is mortified by it, except the love of truth;
and that passion never is, nor can be, carried to too high a degree. It
is surprising, therefore, that this philosophy, which, in almost every
instance, must be harmless and innocent, should be the subject of so
much groundless reproach and obloquy. But, perhaps, the very
circumstance which renders it so innocent is what chiefly exposes it to
the public hatred and resentment. By flattering no irregular passion, it
gains few partizans: By opposing so many vices and follies, it raises to
itself abundance of enemies, who stigmatize it as libertine, profane, and
irreligious.

\marginnote{\smaller5.2}[0cm]Nor need we fear that this philosophy, while it endeavors to limit our
enquiries to common life, should ever undermine the reasonings of common
life, and carry its doubts so far as to destroy all action, as well as
speculation. Nature will always maintain her rights, and prevail in the
end over any abstract reasoning whatsoever. Though we should conclude,
for instance, as in the foregoing section, that, in all reasonings from
experience, there is a step taken by the mind which is not supported by
any argument or process of the understanding; there is no danger that
these reasonings, on which almost all knowledge depends, will ever be
affected by such a discovery. If the mind be not engaged by argument to
make this step, it must be induced by some other principle of equal
weight and authority; and that principle will preserve its influence as
long as human nature remains the same. What that principle is may well
be worth the pains of enquiry.

\marginnote{\smaller5.3}[0cm]Suppose a person, though endowed with the strongest faculties of
reason and reflection, to be brought on a sudden into this world; he
would, indeed, immediately observe a continual succession of objects,
and one event following another; but he would not be able to discover
anything farther. He 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 and casual. There
may be no reason to infer the existence of one from the appearance of
the other. And in a word, such a person, without more experience, could
never employ his conjecture or reasoning concerning any matter of fact,
or be assured of anything beyond what was immediately present to his
memory and senses.

\marginnote{\smaller5.4}[0cm]Suppose, again, that he has acquired more experience, and has lived so
long in the world as to have observed familiar objects or events to be
constantly conjoined together; what is the consequence of this
experience? 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 secret power by which the one object
produces the other; nor is it, by any process of reasoning, he is
engaged to draw this inference. But still he finds himself determined to
draw it: And though he should be convinced that his understanding has no
part in the operation, he would nevertheless continue in the same course
of thinking. There is some other principle which determines him to form
such a conclusion.

\marginnote{\smaller5.5}[0cm]This principle is \textbf{custom} or \textbf{habit}. For wherever the repetition of
any particular act or operation produces a propensity to renew the same
act or operation, without being impelled by any reasoning or process of
the understanding, we always say, that this propensity is the effect of
\textit{custom}. By employing that word, we pretend not to have given the
ultimate reason of such a propensity. We only point out a principle of
human nature, which is universally acknowledged, and which is well known
by its effects. Perhaps we can push our enquiries no farther, or pretend
to give the cause of this cause; but must rest contented with it as the
ultimate principle, which we can assign, of all our conclusions from
experience. It is sufficient satisfaction, that we can go so far,
without repining at the narrowness of our faculties because they will
carry us no farther. And it is certain we here advance a very
intelligible proposition at least, if not a true one, when we assert
that, 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. This hypothesis seems
even the only one which explains the difficulty, why we draw, from a
thousand instances, an inference which we are not able to draw from one
instance, that is, in no respect, different from them. Reason is
incapable of any such variation. The conclusions which it draws from
considering one circle are the same which it would form upon surveying
all the circles in the universe. But no man, having seen only one body
move after being impelled by another, could infer that every other body
will move after a like impulse. All inferences from experience,
therefore, are effects of custom, not of reasoning.\footnote{Nothing is more useful than for writers, even, on \textit{moral},
    \textit{political}, or \textit{physical} subjects, to distinguish between
    \textit{reason} and \textit{experience}, and to suppose, that these species
    of argumentation are entirely different from each other. The
    former are taken for the mere result of our intellectual
    faculties, which, by considering \textit{a priori} the nature of
    things, and examining the effects, that must follow from their
    operation, establish particular principles of science and
    philosophy. The latter are supposed to be derived entirely from
    sense and observation, by which we learn what has actually
    resulted from the operation of particular objects, and are
    thence able to infer, what will, for the future, result from
    them. Thus, for instance, the limitations and restraints of
    civil government, and a legal constitution, may be defended,
    either from \textit{reason}, which reflecting on the great frailty and
    corruption of human nature, teaches, that no man can safely be
    trusted with unlimited authority; or from \textit{experience} and
    history, which inform us of the enormous abuses, that ambition,
    in every age and country, has been found to make of so
    imprudent a confidence.

    The same distinction between reason and experience is
    maintained in all our deliberations concerning the conduct of
    life; while the experienced statesman, general, physician, or
    merchant is trusted and followed; and the unpractised novice,
    with whatever natural talents endowed, neglected and despised.
    Though it be allowed, that reason may form very plausible
    conjectures with regard to the consequences of such a
    particular conduct in such particular circumstances; it is
    still supposed imperfect, without the assistance of experience,
    which is alone able to give stability and certainty to the
    maxims, derived from study and reflection.

    But notwithstanding that this distinction be thus universally
    received, both in the active speculative scenes of life, I
    shall not scruple to pronounce, that it is, at bottom,
    erroneous, at least, superficial.

    If we examine those arguments, which, in any of the sciences
    above mentioned, are supposed to be the mere effects of
    reasoning and reflection, they will be found to terminate, at
    last, in some general principle or conclusion, for which we can
    assign no reason but observation and experience. The only
    difference between them and those maxims, which are vulgarly
    esteemed the result of pure experience, is, that the former
    cannot be established without some process of thought, and some
    reflection on what we have observed, in order to distinguish
    its circumstances, and trace its consequences: Whereas in the
    latter, the experienced event is exactly and fully familiar to
    that which we infer as the result of any particular situation.
    The history of a Tiberius or a Nero makes us dread a like
    tyranny, were our monarchs freed from the restraints of laws
    and senates: But the observation of any fraud or cruelty in
    private life is sufficient, with the aid of a little thought,
    to give us the same apprehension; while it serves as an
    instance of the general corruption of human nature, and shows
    us the danger which we must incur by reposing an entire
    confidence in mankind. In both cases, it is experience which is
    ultimately the foundation of our inference and conclusion.

    There is no man so young and unexperienced, as not to have
    formed, from observation, many general and just maxims
    concerning human affairs and the conduct of life; but it must
    be confessed, that, when a man comes to put these in practice,
    he will be extremely liable to error, till time and farther
    experience both enlarge these maxims, and teach him their
    proper use and application. In every situation or incident,
    there are many particular and seemingly minute circumstances,
    which the man of greatest talent is, at first, apt to overlook,
    though on them the justness of his conclusions, and
    consequently the prudence of his conduct, entirely depend. Not
    to mention, that, to a young beginner, the general observations
    and maxims occur not always on the proper occasions, nor can be
    immediately applied with due calmness and distinction. The
    truth is, an unexperienced reasoner could be no reasoner at
    all, were he absolutely unexperienced; and when we assign that
    character to any one, we mean it only in a comparative sense,
    and suppose him possessed of experience, in a smaller and more
    imperfect degree.}

\marginnote{\smaller5.6}[0cm]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. Without the influence of custom, we should be entirely ignorant of every
matter of fact beyond what is immediately present to the memory and
senses. We should never know how to adjust means to ends, or to employ
our natural powers in the production of any effect. There would be an
end at once of all action, as well as of the chief part of speculation.

\marginnote{\smaller5.7}[0cm]But here it may be proper to remark, that though our conclusions
from experience carry us beyond our memory and senses, and assure us of
matters of fact which happened in the most distant places and most
remote ages, yet some fact must always be present to the senses or
memory, from which we may first proceed in drawing these conclusions. A
man, who should find in a desert country the remains of pompous
buildings, would conclude that the country had, in ancient times, been
cultivated by civilized inhabitants; but did nothing of this nature
occur to him, he could never form such an inference. We learn the events
of former ages from history; but then we must peruse the volumes in
which this instruction is contained, and thence carry up our inferences
from one testimony to another, till we arrive at the eyewitnesses and
spectators of these distant events. In a word, if we proceed not upon
some fact, present to the memory or senses, our reasonings would be
merely hypothetical; and however the particular links might be connected
with each other, the whole chain of inferences would have nothing to
support it, nor could we ever, by its means, arrive at the knowledge of
any real existence. If I ask why you believe any particular matter of
fact, which you relate, you must tell me some reason; and this reason
will be some other fact, connected with it. But as you cannot proceed
after this manner, \textit{in infinitum}, you must at last terminate in some
fact, which is present to your memory or senses; or must allow that your
belief is entirely without foundation.

\marginnote{\smaller5.8}[0cm]What, then, is the conclusion of the whole matter? A simple one;
though, it must be confessed, pretty remote from the common theories of
philosophy. All belief of matter of fact or real existence is derived
merely from some object, present to the memory or senses, and a
customary conjunction between that and some other object. Or in other
words; having found, in many instances, that any two kinds of
objects--flame and heat, snow and cold--have always been conjoined
together; if flame or snow be presented anew to the senses, the mind is
carried by custom to expect heat or cold, and to \textit{believe} that such a
quality does exist, and will discover itself upon a nearer approach.
This belief is the necessary result of placing the mind in such
circumstances. It is an operation of the soul, when we are so situated,
as unavoidable as to feel the passion of love, when we receive benefits;
or hatred, when we meet with injuries. All these operations are a
species of natural instincts, which no reasoning or process of the
thought and understanding is able either to produce or to prevent.\footnote{[5.9--22 are omitted.]}


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