SCEPTICAL DOUBTS CONCERNING THE
OPERATIONS OF THE UNDERSTANDING
PART I.
20. All the objects of human reason or enquiry may
naturally be divided into two kinds, to wit, Relations of Ideas, and
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. 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. 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.
21. 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. That the sun will not
rise to-morrow is no less intelligible a proposition, and implies no more
contradiction than the affirmation, that it will rise. 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.
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.
22. All reasonings concerning matter of fact seem
to be founded on the relation of Cause and Effect. By means of that
relation alone we can go beyond the evidence of our memory and senses. 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 connexion 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.
23. 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.
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 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.
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.
24. This proposition, 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 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?
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.
25. 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 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? 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 connexion 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 a priori will never be able
to show us any foundation for this preference.
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, 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.
26. 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 endeavours to elude or avoid it.
27. 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 a
priori, and consider merely any object or cause, as it appears to the mind,
independent of all observation, it never could suggest to us the notion of any
distinct object, such as its effect; much less, show us the inseparable and
inviolable connexion between them. 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.
PART II.
28. 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, 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, What is
the foundation of all our reasonings and conclusions concerning that
relation? it may be replied in one word, Experience. But if we still carry
on our sifting humour, and ask, 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.
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 not founded on reasoning, or any
process of the understanding. This answer we must endeavour both to explain and
to defend.
29. 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 and principles on which the influence of those objects entirely
depends. Our senses inform us of the colour, 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
powers6
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 colour 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 connexion 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 Experience, it can be allowed to give direct
and 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, I have found that such an object
has always been attended with such an effect, and 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 connexion 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.
30. 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, endeavour to show that none of them can afford such
an argument.
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 tact 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 priori.
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
endeavour, therefore, the proof of this last supposition by probable arguments,
or arguments regarding existence, must be evidently going in a circle, and
taking that for granted, which is the very point in question.
31. 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 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.
32. Should it be said that, from a number of
uniform experiments, we infer a connexion 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
inference is founded? Where is the medium, the interposing ideas, which
join propositions so very wide of each other? It is confessed that the colour,
consistence, and other sensible qualities of bread appear not, of themselves, to
have any connexion 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 colour 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, I have found, in all past instances, such sensible qualities
conjoined with such secret powers. And when he says, 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.
33. 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.
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 pretence 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.
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