Thomas Reid.

The works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters online

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son : they do the office of reason while it is
in its infancy, and must, as it were, be car-
ried in a nurse's arms, and they are leading-
strings to it in its gradual progress.

From what has been said, I think it ap-
pears that our original powers of perceiving
objects by our senses receive great improve-
ment by use and habit ; and without this
improvement, would be altogether insuf-
ficient for the purposes of life. The daily
occurrences of life not only add to our stock
of knowledge, but give additional percep-
tive powers to our senses ; and time gives
us the use of our eyes and ears, as well as
of our hands and legs.

This is the greatest and most important
improvement of our external senses. It is
to be found in all men come to years of un-
derstanding, but it is various in different
persons according to their different occupa-
tions, and the different circumstances in
which they are placed. Every artist re-
quires an eye as well as a hand in his own
profession ; his eye becomes skilled in per-
ceiving, no less than his hand in executing,
what belongs to his employment.

Besides this improvement of our senses,
which nature produces without our inten-
tion, there are various ways in which they
may be improved, or their defects re-
medied by art. As, first, by a due care of
the organs of sense, that they be in a sound
and natural state. This belongs to the de-
partment of the medical faculty.

Secondly, By accurate attention to the
objects of sense. The effects of such atten-
tion in improving our senses, appear in every
art. The artist, by giving more attention
to certain objects than others do, by that
means perceives many things in those ob-
jects which others do not. [286] Those
who happen to be deprived of one sense,
frequently supply that defect in a great de-
gree, by giving more accurate attention to
the objects of the senses they have. The
blind have often been known to acquire un-
common acuteness in distinguishing things
by feeling and hearing ; and the deaf are
uncommonly quick in reading men's thoughts
in their countenance

A third way in which our senses admit of

improvement, is, by add : tirnal organs, or in-
struments contrived by art. By the inven-
tion of optical glasses, and the gradual im-
provement of Ihem, the natural power of
vision is wonderfully improved, and a vast
addition made to the stock of knowledge
which we acquire by the eye. By speaking-
trumpets and -ear-trumpets some improve-
ment has been made in the sense of hearing-
Whether by similar inventions the other
senses may be improved, seems uncertain.

A fourth method by which the informa-
tion got by our senses may be improved, is,
by discovering the connection which nature
hath established between the sensible quali-
ties of objects,and their more latent qualities.

By the sensible qualities of bodies, I un-
derstand those that are perceived immedi-
ately by the senses, ■ such as their colour,
figure, feeling, sound, taste, smell. The
various modifications and various combin-
ations, of these, are innumerable; so that
there are hardly two individual bodies in
Nature that may not be distinguished by
their sensible qualities.

The latent qualities are such as are not
immediately discovered by our senses ; but
discovered sometimes by accident, some-
times by experiment or observation. The
most important part of our knowledge of
bodies is the knowledge of the latent qua-
lities of the several species, by which they
are adapted to certain purposes, either fur
food, or medicine, or agriculture, or for the
materials or utensils of some art or manu-
facture. [287]

I am taught that certain species of bodies
have certain latent qualities ; but how shall
I know that this individual is of such u
species ? This must be known by the sen-
sible qualities which characterise the species.
I must know that this is bread, and that
wine, before I eat the one or drink the
other. I must know that this is rhubarb,
and that opium, before I use the one or the
other for medicine.

It is one branch of human knowledge to
know the names of the various species of
natural and artificial. bodies, and to know
the sensible qualities by which they are
ascertained to be of such a species, and by
which they are distinguished from one an-
other. It is another branch of knowledge
to know the latent qualities of the several
species, and the uses to which they are

The man who possesses both these
branches is informed, by his senses, of in-
numerable things of real moment which are
hid from those who possess only one, or
neither. This is an improvement in the
information got by our senses, which must
keep pace with the improvements made is
natural history, in natural philosophy, and
in the arts.



[essay n.

It would be an improvement BtiU higher
if we were able to discover any connection
between the sensible qualities of bodies and
their latent qualities, without knowing the
species, or what may have been discovered
with regard to it.

Some philosophers, of the first rate, have
made attempts towards this noble improve-
ment, not without promising hopes of suc-
cess. Thus, the celebrated Linnseus has
attempted to point out certain sensible qua-
lities by which a plant may very probably
be concluded to be poisonous without know-
ing its name or species. He has given se-
veral other instances, wherein certain medi-
cal and economical virtues of plants are
indicated by their external appearances.
Sir Isaac Newton hath attempted to shew
that, from the colours of bodies, we may
form a probable conjecture of the size of
their constituent parts, by which the rays
of light are reflected. [288]

No man can pretend to set limits to the
discoveries that may be made by human
genius and industry, of such connections
between the latent and the sensible quali-
ties of bodies. A wide field here opens to
our view, whose boundaries no man can
ascertain, of improvements that may here-
after be made in the information conveyed
to us by our senses.



Complaints of the fallacy of the senses
have been very common in ancient and in
modern times, especially among the philo-
sophers. And, if we should take for granted
all that they have said on this subject, the
natural conclusion from it might seem to
be, that the senses are given to us by some
malignant demon on purpose to delude us,
rather than that they are formed by the
wise and beneficent Author of Nature, to
give us true information of things necessary
to our preservation and happiness.

The whole sect of atomists among the
ancients, led by Democritus, and afterwards
by Epicurus, maintained that all the quali-
ties of bodies which the moderns call se-
condary qualities — to wit, smell, taste, sound,
colour, heat, and cold — are mere illusions of
sense, and have no real existence.* Plato
maintained that we can attain no real know-
ledge of material things ; and that eternal
and immutable ideas are the only objects of
real knowledge. The academics and scep-
tics anxiously sought for arguments to
prove the fallaciousness of our senses, in
order to support their favourite doctrine,

* Not correctly stated. See above, p. 316, note §.
The Epicureans denied the fallacy of Sense.— H.

that even in things that seem most evident,
we ought to withhold assent. [289 J

Among the Peripatetics we find frequent
complaints that the senses often deceive us,
and that their testimony is to he suspected,
when it is not confirmed by reason, by which
the errors of sense may be corrected. This
complaint they supported by many com-
monplace instances : such as, the crooked
appearance of an oar in water ; objects being
magnified, and their distance mistaken, iu
a fog ; the sun and moon appearing about
a foot or two in diameter, while they are
really thousands of miles ; a square tower
being taken at a distance to be round. These,
and many similar appearances, they thought
to be sufficiently accounted for from the
fallacy of the senses : and thus the fallacy
of the senses was used as a decent cover to
conceal their ignorance of the real causes of
such phsenomena, and served the same pur-
pose as their occult qualities and substantial
forms. "

Dts Cartes and his followers joined iu
the same complaint. Antony le Grand, a
philosopher of that sect, in the first chapter
of his Logic, expresses the sentiments of
the sect as follows : " Since all our senses are
fallacious, and we are frequently deceived
by them, common reason advises that we
should not put too much trust-in them, nay,
that we should suspect falsehood in every-
thing they represent ; for it is imprudence
and temerity to trust to those who have but
oncedeceivedus; and, if they err at anytime,
they may be believed always to err. They
are given by nature for this purpose only
to warn us of what is useful and what ia
hurtful to us. The order of Nature is per-
verted when we put them to any other
use, and apply them for the knowledge of

When we consider that the active part
of 'mankind, in all ages from the beginning
of the world, have rested their most import-
ant concerns upon the testimony of sense,
it will be very difficult to reconcile their
conduct with the speculative opinion so
generally entertained of the fallaciousness
of the senses. [290] And it seems to be
a very unfavourable account of the work-
manship of the Supreme Being, to think
that he has given us ono faculty to deceive
us — to wit, our senses ; and another faculty
— to wit, our reason — to detect the fallacy.

It deserves, therefore, to be considered,
whether the fallaciousness of our senses be
not a common error, which men have been
led into, from a desire to conceal their igno-
rance, or to apologize for their mistakes.

There are two powers which we owe to

* A very inaccurate representation of the Peripa-
tetic doctrine touching this matter. In fact, the Ari-
stotelian doctrine, and that of Reid himself, are
almost the same. — II.




our external senses— sensation, and the per-
ception of external objects.

It is impossible that there can be any
fallacy in sensation : for we are conscious of
all our sensations, and they can neither be
any other in their nature, nor greater or
less in their degree than we feel them. It
is impossible that a man should be in pain,
when he does not feel pain ; and when he
feels pain, it is impossible that his pain
should not be real, and in its degree what
it is felt to be ; and the same thing may be
said of every sensation whatsoever. Ah
agreeable or an uneasy sensation may be
forgot when it is past, but when it is pre-
sent, it can be nothing but what we feel.

If, therefore, there be any fallacy in our
senses, it must be in the perception of ex-
ternal objects, which we shall next con-

And here I grant that we can conceive
powers of perceiving external objects more
perfect than ours, which, possibly, beings of a
higher order may enjoy. We can perceive
external objects only by means of bodily or-
gans ; and these are liable to various dis-
orders, which sometimes affect our powers
of perception. The nerves and brain, which
are interior organs of perception, are like-
wise liable to disorders, as every part of the
human frame is. [291]

The imagination, the memory, the judging
and reasoning powers, are all liable to be
hurt, or even destroyed, by disorders of the
body, as well as our powers of perception ;
but we do not on this account call them

Our senses, our memory, and our reason,
are all limited and imperfect— this is the
lot of humanity : but they are such as the
Author of our being saw to be best fitted
for us in our present state. Superior natures
may have intellectual powers which we have
not, or such as we have, in a more perfect
degree, and less liable to accidental disor-
ders ; but we have no reason to think that
God has given fallacious powers to any of
nis creatures : this would be to think dis-
honourably of our Maker, and would lay a
foundation for universal scepticism.

The appearances commonly imputed to
the fallacy of the senses are many and of
different kinds; but I think they may be
reduced to the four following classes.

First, Many things called deceptions of
the senses are'only conclusions rashly drawn
from the testimony of the senses. In these
cases the testimony of the senses is true,
but we rashly draw a conclusion from it,
which does not necessarily follow. We are
disposed to impute our errors rather to false
information than to inconclusive reasoning,
and to blame our senses for the wrong con-
clusions we draw from their testimony.

Thus, when a man has taken a counter -

feit guinea for a true one, he says his senses
deceived him ; but he lays the blame where
it ought not to be laid : for we may ask him,
Did your senses give a false testimony of
the colour, or of the figure, or of the im-
pression ? No. But this is all that they
testified, and this they testified truly : From
these premises you concluded that it was a
true guinea, but this conclusion does not
follow ; you erred, therefore, not by relying
upon the testimony of sense, but by judging
rashly from its testimony. [292] Not only
are your senses innocent of this error, but
it is only by their information that it can be
discovered. If you consult them properly,
they will inform you that what you took for
a guinea is base metal, or is deficient in
weight, and this can only be known by the
testimony of sense.

I remember to have met with a man who
thought the argument used by Protestants
against the Popish doctrine of transubstan-
tiation, from the testimony of our senses,
inconclusive; because, said he, instances
may be given where several of our sensesmay
deceive ua: How do we know then that
there may not be cases wherein they all
deceive us, and no sense is left to detect the
fallacy ? I begged of him to know an in-
stance wherein several of our senses deceive
us. I take, said he, a piece of soft turf ; I
cut it into the shape of an apple ; with the
essence of apples, I give it the smell of an
apple ; and with paint, I can give it the skin
and colour of an apple. Here then is a body,
which, if you judge by your eye, by your
touch, or by your smell, is an apple.

To this I would answer, that no one of
our senses deceives us in this case. My
sight and touch testify that it has the shape
and colour of an apple : this is true. The
sense of smelling testifies that it has the
smell of an apple : this is likewise true, and
is no deception. Where then lies the de-
ception ? It is evident it lies in this — that
because this body has some qualities belong-
ing apple I conclude that it is an apple.
This is a fallacy, not of the senses, but of
inconclusive .reasoning.

Many false judgments that are accounted
deceptions of sense, arise from our mistaking
relative motion for real or absolute motion.
These no deceptions of sense, because
by our senses we perceive only the relative
motions of bodies ; and it is by reasoning
that we infer the real from therelative which
we perceive. A little reflection may satisfy
us of this. [293]

It was before observed, that we perceive
extension to be one sensible quality of
bodies, and thence are necessarily led to
conceive space, though space be of itself
no object of sense. When a body is re-
moved out of its place, the space which it
filled remains empty till it is filled by soni6




other body, and would remain if it should
never be filled. Before any body e tisted, the
space which bodies now occupy was empty
space, capable of receiving bodies ; for no
body can exist where there is no space to
contain it. There is space therefore when-
ever bodies exist, or can exist.

Hence it is evident that space can have
no limits. It is no less evident that it is
immovable. Bodies placed in it are mov-
able, but the place where they were cannot
be moved ; and we can as easily conceive a
thing to be moved from itself, as one part
of space brought nearer to or removed
farther from another.

The space, therefore, which is unlimited
and immovable, is called by philosophers
absolute space. Absolute or real motion is
a change of place in absolute space.

Our senses do not testify the absolute
motion or absolute rest of any body. When
one body removes from another, this may
be discerned by the senses ; but whether
any body keeps the same part of absolute
space, we do not perceive by our senses.
When one body seems to remove from an-
other, we can infer with certainty that there
is absolute motion, but whether in the one
or the other, or partly in both, is not dis-
cerned by sense.

Of all the prejudices which philosophy
contradicts, I believe there is none so general
as that the earth keeps its place unmoved.
This opinion seems to be universal, till it
is corrected by instruction or by philoso-
phical speculation. Those who have any
tincture of education are not now in danger
of being held by it, but they find at first a
reluctance to believe that there are anti-
podes ; that the earth is spherical, and turns
round its axis every day, and round the sun
every year : they can recollect the time
when reason struggled with prejudice upon
these points, and prevailed at length, but
not without some effort. [294]

The cause of a prejudice so very general
is not unworthy of investigation. But. that
is not our present business. It is sufficient
to observe, that it cannot justly be called a
fallacy of sense ; because our senses testify
only the change of situation of one body in
relation to other bodies, and not its change
of situation in absolute space. It is only
the relative motion of bodies that we per-
ceive, and that we perceive truly. It is
the province of reason and philosophy, from
the relative motions which we perceive, to
collect the real and absolute motions which
produce them.

All motion must be estimated from some
point or place which is supposed to be at
rest. We perceive not the points of abso-
lute space, from which real and absolute
motion must be reckoned ; And there are
obvious reasons that lead mankind in the

state of ignorance, to make the earth the
fixed place from which they may estimate
the various motions they perceive. The
custom of doing this from infancy, and of
using constantly a language which supposes
the earth to be at rest, may perhaps be the
cause of the general prejudice in favour of
this opinion.

Thus it appears that, if we distinguish
accurately between what our senses really
and naturally testify, and the conclusions
which we draw from their testimony by
reasoning, we shall find many of the errors,
called fallacies of the senses, to be no fal-
lacy of the senses, but rash judgments,
which are not to be imputed to our senses.

Secondly, Another class of errors imputed
to the fallacy of the senses, are those which
we are liable to in our acquired perceptions.
Acquired perception is not properly the
testimony of those senses which God hath
given us, but a conclusion drawn from what
the senses testify. [295] In our past ex-
perience, we have found certain things con-
joined with what our senses testify. We
are led by our constitution to expect this
conjunction in time to come ; and when
we have often found it in our experience + o
happen, we acquire a firm belief that the
things which we have found thus conjoined,
are connected in nature, and that one is a
sign of the other. The appearance of the
sign immediately produces the belief of its
usual attendant, and we think we perceive
the one as well as the other.

That such conclusions are formed even
in infancy, no man can doubt : nor is it less
certain that they are confounded with the
natural and immediate perceptions of sense,
and in all languages are called by the same
name. We are therefore authorized by
language to call them perception, and must
often do so, or speak unintelligibly. But
philosophy teaches us, in this, as in many
other instances, to distinguish things which
the vulgar confound. I have therefore
given the name of acquired perception to
such conclusions, to distinguish them from
what is naturally, originally, and imme-
diately testified by our senses. Whether
this acquired perception is to be resolved
into some process of reasoning, of which
we have lost the remembrance, as some
philosophers think, or whether it results
from some part of our constitution distinct
from reason, as I rather believe, does not
concern the present subject. If the first
of these opinions be true, the errors of ac-
quired perception will fall under the first
class before mentioned. If not, it makes
a distinct class by itself. But whether the
one or the other be true, it must be
observed that the errors of acquired per-
ception are not properly fallacies of our

[294. 2951



Thug, when a globe is set before me, I
perceive by my eyes that it has three di-
mensions and a spherical figure. To say
that this is not perception, would be to
reject the authority of custom in the use of
words, which no wise man will do : but
that it is not the testimony of my sense of
seeing, every philosopher knows. I see
only a circular form, having the light and
colour distributed in a certain way over it.
[296] But, being accustomed to observe
this distribution of light and colour only in
a spherical body, I immediately, from what
I see, believe the object to be spherical, and
say that I see or perceive it to be spherical.
When a painter, by an exact imitation of
that distribution of light and colour which
I have been accustomed to see only in a
real sphere, deceives me, so as to make me
take that to be a real sphere which is only a
painted one, the testimony of my eye is true
— the colour and visible figure of the object
is truly what I see it to be : the error lies
in the conclusion drawn from what I see —
to wit, that the object has three dimensions
and a spherical figure. The conclusion is
false in this case ; but, whatever be the
origin of this conclusion, it is not properly
the testimony of sense.

To this class we must refer the judg-
ments we are apt to form of the distance
and magnitude of the heavenly bodies, and
of terrestrial objects seen on high- The
mistakes we make of the magnitude and
distance of objects seen through optical
glasses, or through an atmosphere uncom-
monly clear or uncommonly foggy, belong
likewise to this class.

The errors we are led into in acquired
perception are very rarely hurtful to us in
the conduct of life ; they are gradually cor-
rected by a more enlarged experience^ and
a more perfect knowledge of the laws of
Nature : and the general laws of our con-
stitution, by which we are sometimes led
into them, are of the greatest utility.

We come into the world ignorant of
everything, and by our ignorance exposed
to many dangers and to many mistakes. The
regular train of causes and effects, which
divine wisdom has established, and which
directs every step of our conduct in advanced
life, is unknown, until it is gradually dis-
covered by experience. [297]

We must learn much from experience
before we can reason, and therefore must be
liable to many errors. Indeed, I apprehend,
that, in the first part of life, reason would do
us much more hurt than good Were we
sensible of our condition in that period, and
capable of reflecting upon it, we snould be
like a man in the dark, surrounded with
dangers, where every step he takes may be
into a pit. Reason would direct him to sit
flown, and wait till he could see about him.

In like manner, if we suppose an infant
endowed with reason, it would direct him
to do nothing, till he knew what could be
done with safety. This he can only know
by experiment, and experiments are danger-
ous. Reason directs, that experiments that
are full of danger should not be made with-
out a very urgent cause. It would there-
fore make the infant unhappy, and hinder
his improvement by experience.

Nature has followed another plan. The
child, unapprehensive of danger, is led by
instinct to exert all his active powers, to
try everything without the cautious admo-
nitions of reason, and to believe everything
that is told him. Sometimes he suffers by

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 76 of 114)