An Enquiry Concerning Human Understanding, David Hume [online e book reader TXT] 📗

prove, that the senses alone are not implicitly to be

depended on; but that we must correct their evidence by reason, and by

considerations, derived from the nature of the medium, the distance of

the object, and the disposition of the organ, in order to render them,

within their sphere, the proper criteria of truth and falsehood. There

are other more profound arguments against the senses, which admit not of

so easy a solution.

 

118. It seems evident, that men are carried, by a natural instinct or

prepossession, to repose faith in their senses; and that, without any

reasoning, or even almost before the use of reason, we always suppose an

external universe, which depends not on our perception, but would exist,

though we and every sensible creature were absent or annihilated. Even

the animal creation are governed by a like opinion, and preserve this

belief of external objects, in all their thoughts, designs, and actions.

 

It seems also evident, that, when men follow this blind and powerful

instinct of nature, they always suppose the very images, presented by

the senses, to be the external objects, and never entertain any

suspicion, that the one are nothing but representations of the other.

This very table, which we see white, and which we feel hard, is believed

to exist, independent of our perception, and to be something external

to our mind, which perceives it. Our presence bestows not being on it:

our absence does not annihilate it. It preserves its existence uniform

and entire, independent of the situation of intelligent beings, who

perceive or contemplate it.

 

But this universal and primary opinion of all men is soon destroyed by

the slightest philosophy, which teaches us, that nothing can ever be

present to the mind but an image or perception, and that the senses are

only the inlets, through which these images are conveyed, without being

able to produce any immediate intercourse between the mind and the

object. The table, which we see, seems to diminish, as we remove farther

from it: but the real table, which exists independent of us, suffers no

alteration: it was, therefore, nothing but its image, which was present

to the mind. These are the obvious dictates of reason; and no man, who

reflects, ever doubted, that the existences, which we consider, when we

say, this house and that tree, are nothing but perceptions in the

mind, and fleeting copies or representations of other existences, which

remain uniform and independent.

 

119. So far, then, are we necessitated by reasoning to contradict or

depart from the primary instincts of nature, and to embrace a new system

with regard to the evidence of our senses. But here philosophy finds

herself extremely embarrassed, when she would justify this new system,

and obviate the cavils and objections of the sceptics. She can no longer

plead the infallible and irresistible instinct of nature: for that led

us to a quite different system, which is acknowledged fallible and even

erroneous. And to justify this pretended philosophical system, by a

chain of clear and convincing argument, or even any appearance of

argument, exceeds the power of all human capacity.

 

By what argument can it be proved, that the perceptions of the mind

must be caused by external objects, entirely different from them, though

resembling them (if that be possible) and could not arise either from

the energy of the mind itself, or from the suggestion of some invisible

and unknown spirit, or from some other cause still more unknown to us?

It is acknowledged, that, in fact, many of these perceptions arise not

from anything external, as in dreams, madness, and other diseases. And

nothing can be more inexplicable than the manner, in which body should

so operate upon mind as ever to convey an image of itself to a

substance, supposed of so different, and even contrary a nature.

 

It is a question of fact, whether the perceptions of the senses be

produced by external objects, resembling them: how shall this question

be determined? By experience surely; as all other questions of a like

nature. But here experience is, and must be entirely silent. The mind

has never anything present to it but the perceptions, and cannot

possibly reach any experience of their connexion with objects. The

supposition of such a connexion is, therefore, without any foundation in

reasoning.

 

120. To have recourse to the veracity of the supreme Being, in order to

prove the veracity of our senses, is surely making a very unexpected

circuit. If his veracity were at all concerned in this matter, our

senses would be entirely infallible; because it is not possible that he

can ever deceive. Not to mention, that, if the external world be once

called in question, we shall be at a loss to find arguments, by which we

may prove the existence of that Being or any of his attributes.

 

121. This is a topic, therefore, in which the profounder and more

philosophical sceptics will always triumph, when they endeavour to

introduce an universal doubt into all subjects of human knowledge and

enquiry. Do you follow the instincts and propensities of nature, may

they say, in assenting to the veracity of sense? But these lead you to

believe that the very perception or sensible image is the external

object. Do you disclaim this principle, in order to embrace a more

rational opinion, that the perceptions are only representations of

something external? You here depart from your natural propensities and

more obvious sentiments; and yet are not able to satisfy your reason,

which can never find any convincing argument from experience to prove,

that the perceptions are connected with any external objects.

 

122. There is another sceptical topic of a like nature, derived from the

most profound philosophy; which might merit our attention, were it

requisite to dive so deep, in order to discover arguments and

reasonings, which can so little serve to any serious purpose. It is

universally allowed by modern enquirers, that all the sensible qualities

of objects, such as hard, soft, hot, cold, white, black, &c. are merely

secondary, and exist not in the objects themselves, but are perceptions

of the mind, without any external archetype or model, which they

represent. If this be allowed, with regard to secondary qualities, it

must also follow, with regard to the supposed primary qualities of

extension and solidity; nor can the latter be any more entitled to that

denomination than the former. The idea of extension is entirely acquired

from the senses of sight and feeling; and if all the qualities,

perceived by the senses, be in the mind, not in the object, the same

conclusion must reach the idea of extension, which is wholly dependent

on the sensible ideas or the ideas of secondary qualities. Nothing can

save us from this conclusion, but the asserting, that the ideas of those

primary qualities are attained by Abstraction, an opinion, which, if

we examine it accurately, we shall find to be unintelligible, and even

absurd. An extension, that is neither tangible nor visible, cannot

possibly be conceived: and a tangible or visible extension, which is

neither hard nor soft, black nor white, is equally beyond the reach of

human conception. Let any man try to conceive a triangle in general,

which is neither Isosceles nor Scalenum, nor has any particular

length or proportion of sides; and he will soon perceive the absurdity

of all the scholastic notions with regard to abstraction and

general ideas[31]

 

[31] This argument is drawn from Dr. Berkeley; and indeed most

of the writings of that very ingenious author form the best

lessons of scepticism, which are to be found either among the

the ancient or modern philosopher, Bayle not excepted. He

professes, however, in his title-page (and undoubtedly with

great truth) to have composed his book against the sceptics as

well as against the atheists and free-thinkers. But that all

his arguments, though otherwise intended, are, in reality,

merely sceptical, appears from this, _that they admit of no

answer and produce no conviction_. Their only effect is to

cause that momentary amazement and irresolution and confusion,

which is the result of scepticism.

 

123. Thus the first philosophical objection to the evidence of sense or

to the opinion of external existence consists in this, that such an

opinion, if rested on natural instinct, is contrary to reason, and if

referred to reason, is contrary to natural instinct, and at the same

time carries no rational evidence with it, to convince an impartial

enquirer. The second objection goes farther, and represents this opinion

as contrary to reason: at least, if it be a principle of reason, that

all sensible qualities are in the mind, not in the object. Bereave

matter of all its intelligible qualities, both primary and secondary,

you in a manner annihilate it, and leave only a certain unknown,

inexplicable something, as the cause of our perceptions; a notion so

imperfect, that no sceptic will think it worth while to contend

against it.

 

PART II.

 

124. It may seem a very extravagant attempt of the sceptics to destroy

reason by argument and ratiocination; yet is this the grand scope of

all their enquiries and disputes. They endeavour to find objections,

both to our abstract reasonings, and to those which regard matter of

fact and existence.

 

The chief objection against all abstract reasonings is derived from

the ideas of space and time; ideas, which, in common life and to a

careless view, are very clear and intelligible, but when they pass

through the scrutiny of the profound sciences (and they are the chief

object of these sciences) afford principles, which seem full of

absurdity and contradiction. No priestly dogmas, invented on purpose

to tame and subdue the rebellious reason of mankind, ever shocked common

sense more than the doctrine of the infinitive divisibility of

extension, with its consequences; as they are pompously displayed by all

geometricians and metaphysicians, with a kind of triumph and exultation.

A real quantity, infinitely less than any finite quantity, containing

quantities infinitely less than itself, and so on in infinitum; this

is an edifice so bold and prodigious, that it is too weighty for any

pretended demonstration to support, because it shocks the clearest and

most natural principles of human reason.[32] But what renders the matter

more extraordinary, is, that these seemingly absurd opinions are

supported by a chain of reasoning, the clearest and most natural; nor is

it possible for us to allow the premises without admitting the

consequences. Nothing can be more convincing and satisfactory than all

the conclusions concerning the properties of circles and triangles; and

yet, when these are once received, how can we deny, that the angle of

contact between a circle and its tangent is infinitely less than any

rectilineal angle, that as you may increase the diameter of the circle

in infinitum, this angle of contact becomes still less, even _in

infinitum_, and that the angle of contact between other curves and their

tangents may be infinitely less than those between any circle and its

tangent, and so on, in infinitum? The demonstration of these

principles seems as unexceptionable as that which proves the three

angles of a triangle to be equal to two right ones, though the latter

opinion be natural and easy, and the former big with contradiction and

absurdity. Reason here seems to be thrown into a kind of amazement and

suspence, which, without the suggestions of any sceptic, gives her a

diffidence of herself, and of the ground on which she treads. She sees a

full light, which illuminates certain places; but that light borders

upon the most profound darkness. And between these she is so dazzled and

confounded, that she scarcely can pronounce with certainty and assurance

concerning any one object.

 

[32] Whatever disputes there may be about