Thomas Reid.

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

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fore, it is not a reduetio ad aCsurdttm.—H.

not even have been able to acquire that
logic which suggests these sceptical doubts
with regard to my senses. Therefore, I
consider this instinctive belief as one of the
best gifts of Nature. I thank the Author of
my being, who bestowed it upon me before
the eyes of my reason were opened, and
still bestows it upon me, to be my guide
where reason leaves me in the dark. And
now I yield to the direction of my senses,
not from instinct only, but from confidence
and trust in a faithful and beneficent Moni-
tor, grounded upon the experience of his
paternal care and goodness.

In all this, I deal with the Author of my
being, no otherwise than I thought it reason-
able to deal with my parents and tutors. I
believed by instinct whatever they told me,
long before I had the idea of a he, or thought
of the possibility of their deceiving me.
Afterwards, upon reflection, I found they
had acted like fair and honest people, who
wished me well. I found that, if I had not
believed what they told me, before I could
give a reason of my belief, I had to this day
been little better than a changeling. And
although this natural credulity hath some-
times occasioned my being imposed upon
by deceivers, yet it hath been of infinite
advantage to me upon the whole ; therefore,
I consider it as another good gift of Nature.
And I continue to give that credit, from
reflection, to those of whose integrity and
veracity I have had experience, which be-
fore I gave from instinct.

There is a much greater similitude than
is commonly imagined, between the testi-
mony of nature given by our senses, and
the testimony of men given by language.
The credit we give to both is at first the
effect of instinct* only. When we grow
up, and begin to reason about them, the
credit given to human testimony is re-
strained and weakened, by the experience
we have of deceit. But the credit given to
the testimony of our senses, is established
and confirmed by the uniformity and con-
stancy of the laws of nature.

Our perceptions are of two kinds : some
are natural and original ; others acquired,
and the fruit of experience. When I per-
ceive that this is the taste of cyder, that of
brandy ; that this is the smell of an apple,
that of an orange ; that this is the noise of
thunder, that the ringing of bells ; this the
sound of a coach passing, that the voice of
such a friend : these perceptions, and others
of the same kind, are not original — they are
acquired. But the perception which! have,
by touch, of the hardness and softness of
bodies, of their extension, figure, and mo-
tion, is not acquired — it is original.

* On the propriety of the term " instinct," see in
Note A.— H.



In all our senses, the acquired percep-
tions are many more than the original,
especially in sight. By this sense we per-
ceive originally the visible figure and colour
of bodies onlys and their visible place :*
but we learn to perceive by the eye, almost
everything which we can perceive by
touch. The original perceptions of this
sense serve only as signs to introduce the

The signs by which objects are presented
to us in perception, are the language of
Nature to man ; and as, in many respects,
it hath great affinity with the language of
man to man, so particularly in this, that
both are partly natural and original, partly
acquired by custom. Our original or
natural perceptions are analogous to the
natural language of man to man, of which
we took notice in the fourth chapter ; and
our acquired perceptions are analogous to
artificial language, which, in our mother-
tongue, is got very much in the same man-
ner with our acquired perceptions — as we
shall afterwards more fully explain.

Not only men, but children, idiots, and
brutes, acquire by habit many perceptions
which they had not originally. Almost
every employment in life hath perceptions
of this kind that are peculiar to it. The
shepherd knows every sheep of his flock, as
we do our acquaintance, and can pick them
out of another flock one by one. The
butcher knows by sight the weight and
quality of his beeves and sheep before they
are killed. The farmer perceives by his
eye, very nearly, the quantity of hay in a
rick, or of corn in a heap. The sailor sees
the burthen, the built, and the distance of
a ship at sea, while she is a great way off.
Every man accustomed to writing, distin-
guishes his acquaintance by their hand-
writing, as he does by their faces. And
the painter distinguishes, in the works of his
art, the style of all the great masters. In
a word, acquired perception is very different
in different persons, according to the divers-
ity of objects about which they are em-
ployed, and the application they bestow in
observing them.

Perception ought not only to be distin-
guished from sensation, but likewise from
that knowledge of the objects of sense
which is got by reasoning. There is no
reasoning in perception, as hath been ob-
served. The belief which is implied in it,
is the effect of instinct. But there are
many things, with regard to sensible ob-
jects, which we can infer from what we
perceive ; and such conclusions of reason
ought to be distinguished from what is
merely perceived. When I look at the

# In this passage Reid admits Figure and Place
(consequently, Extension) to be original perceptions
of vision. See above, p. 123, b . note f. — H.

moon, I perceive her to be sometimes cir-
cular, sometimes horned, and sometimes
gibbous. This is simple perception, and is
the same in the philosopher and in the
clown : but from these various appearances
of her enlightened part, I infer that she is
really of a spherical figure. This conclu-
sion is not obtained by simple perception,
but by reasoning. Simple perception has
the same relation to the conclusions of rea-
son drawn from our perceptions, as the
axioms in mathematics have to the pro-
positions. I cannot demonstrate that two
quantities which are equal to the same
quantity, are equal to each other ; neither
can I demonstrate that the tree which
I perceive, exists. But, by the constitution
of my nature, my belief is irresistibly car-
ried along by my apprehension of the
axiom ; and, by the constitution of my
nature, my belief is no less irresistibly car-
ried along by my perception of the tree.
All reasoning is from principles. The first
principles of mathematical reasoning arp
mathematical axioms and definitions ; and
the first principles of all our reasoning
about existences, are our perceptions. The
first principles of every kind of reasoning
are given us by Nature, and are of equal
authority with the faculty of reason itself,
which is also the gift of Nature. The con-
clusions of reason are all built upon first
principles, and can have no other founda-
tion. Most justly, therefore, do such prin-
ciples disdain to be tried by reason, and
laugh at all the artillery of the logician,
when it is directed against them.

When a long train of reasoning is neces-
sary in demonstrating a mathematical pro-
position, it is easily distinguished from an
axiom ; and they seem to be things of a very
different nature. But there are some pro-
positions which lie so near to axioms, that
it is difficult to say whether they ought to
be held as axioms, or demonstrated as pro-
positions. The same thing holds with
regard to perception, and the conclusions
drawn from it. Some of these conclusions
follow our perceptions so easily, and are so
immediately connected with them, that it
is difficult to fix the limit which divides the
one from the other.

Perception, whether original or acquired,
implies no exercise of reason ; and is com-
mon to men, children, idiots, and brutes.
The more obvious conclusions drawn from
our perceptions, by reason, make what we
call common understanding ; by which men
conduct themselves in the common affairs
of life, and by which they are distinguished
from idiots. The more remote conclusions
which are drawn from our perceptions, by
reason, make what we commonly call science
in the various parts of nature, whether in
agriculture, medicine, mechanics, or in any



part of natural philosophy. When I see a
garden in good order, containing a great
variety of things of the best kinds, and in
the most flourishing condition, I immedi-
ately conclude from these signs the skill
and industry of the gardener. A farmer,
when he rises in the morning, and perceives
that the neighbouring brook overflows his
field, concludes that a great deal of rain
hath fallen in the night. Perceiving his
fence broken, and his corn trodden down,
he concludes that some of his own or his
neighbours' cattle have broke loose. Per-
ceiving that his stable-door is broke open,
and some of his horses gone, he concludes
that a thief has carried them off. He traces
the prints of his horses' feet in the soft
ground, and by them discovers which road
the thief hath taken. These are instances
of common understanding, which dwells so
near to perception that it is difficult to trace
the line which divides the one from the other.
In like manner, the science of nature dwells
so near to common understanding that we
cannot discern where the latter ends and the
former begins. I perceive that bodies lighter
than water swim in water, and that those
which are heavier sink. Hence I conclude,
that, if a body remains wherever it is put
under water, whether at the top or bottom,
it is precisely of the same weight with water.
If it will rest only when part of it is above
water, it is lighter than water. And the
greater the part above water is, compared
with the whole, the lighter is the body. If
it had no gravity at all, it would make no
impression upon the water, but stand wholly
above it. Thus, every man, by common
understanding, has a rule by which he
judges of the specific gravity of bodies
which swim in water : and a step or two
more leads him into the science of hydro-

All that we know of nature, or of exist-
ences, may be compared to a tree, which
hath its root, trunk, and branches. In this
tree of knowledge, perception is the root,
common understanding is the trunk, and
the sciences are the branches.

Section XXI.


Although there is no reasoning in per-
ception, yet there are certain means and
instruments, which, by the appointment of
nature, must intervene between the object
and our perception of it ; and, by these,
our perceptions are limited and -regulated.
First, If the object is not in contact with
the organ of sense, there must be some
medium which passes between them. Thus,
in vision, the rays of light ; in hearing, the

vibrations of elastic air; in smelling, the
effluvia of the body smelled — must pass from
the object to the organ ; otherwise we have
no perception. * Secondly, There must be
some action or impression upon the organ
of sense, either by the immediate applica-
tion of the object, or by the medium that
goes between them. Thirdly, The nerves
which go from the brain to the organ must
receive some impression by means of that
which was made upon the organ ; and, pro-
bably, by means of the nerves, some im-
pression must be made upon the brain.
Fourthly, The impression made upon the
organ, nerves, and brain,' is followed by a
sensation. And, last of all, This sensation
is followed by the perception of the object. f

Thus, our perception of objects is the re-
sult of a train of operations ; some of which
affect the body only, others affect the mind.
We know very little of the nature of some
of these operations ; we know not at all how
they are connected together, or in what way
they contribute to that perception which is
the result of the whole ; but, by the laws of
our constitution, we perceive objects in this,
and iu no other way.

There may be other beings who can per-
ceive external objects without rays of light,
or vibrations of air, or effluvia of bodies —
without impressions on bodily organs, or
even without sensations ; but we are so
framed by the Author of Nature, that, even
when we are surrounded by external objects,
we may perceive none of them. Our faculty
of perceiving an object lies dormant, until
it is roused and stimulated by a certain
corresponding sensation. Nor is this sens-
ation always at hand to perform its office ;
for it enters into the mind only in conse-
quence of a certain corresponding impres-
sion made on the organ of sense by the ob-

Let us trace this correspondence of im-
pressions, sensations, and perceptions, as
far as we can — beginning with that which
is first in order, the impression made upon
the bodily organ. But, alas ! we know not
of what nature these impressions are, far
less how they excite sensations in the mind.

We know that one body may act upon
another by pressure, by percussion, by at-
traction, by repulsion, and, probably, in
many other ways which we neither know
nor have names to express. But in which
of these ways objects, when perceived by
us, act upon the organs of sense, these
organs upon the nerves, and the nerves

* The only object of perception is the immediate
object. The distant reality— the mediate object, or
object simply of Reid and other philosophers — is un-
known to the perception of sense, and only reached
by reasoning. — H.

t That sensation prop r precedes perception pro.
per is a false assumption. They are simultaneous
elements of the same indivisible energy H.



upon the brain, we know not. Can any
man tell me how, in vision, the rays of light
act upon the retina, how the retina acts
upon the optic nerve, and how the optic
nerve acts upon the brain ? No man can.
When I feel the pain of the gout in my
toe, I know that there is some unusual im-
pression made upon that part of my body.
But of what kind is it ? Are the small
vessels distended with some redundant
elastic, or'unelastie fluid? Are the fibres
unusually stretched ? Are they torn
asunder by force, or gnawed and corroded
by some acrid humour ? I can answer
none of these questions. All that I feel is
pain, which is not an impression upon the
body, but upon the mind ; and all that I
perceive by this sensation is, that some dis-
temper in my toe occasions this pain. But,
as I know not the natural temper and tex-
ture of my toe when it is at ease, I know as
little what change or disorder of its parts
occasions this uneasy sensation. In like
manner, in every other sensation, there is,
without doubt, some impression made upon
the organ of sense ; but an impression of
which we know not the nature. It is too
subtile to be discovered by our senses, and
we may make a thousand conjectures with-
out coming near the truth. If we under-
stood the structure of our organs of sense
so minutely as to discover what effects are
produced upon them by external objects,
this knowledge would contribute nothing to
our perception of the object ; for they per-
ceive as distinctly who know least about the
manner of perception, as the greatest adepts.
It is necessary that the impression be made
upon our organs, but not that it be known.
"Nature carries on this part of the process
of perception, without our consciousness or

But we cannot be unconscious of the next
step in this process — the sensation of the
mind, which always immediately follows the
impression made upon the body. It is
essential to a sensation to be felt, and it can
be nothing more than we feel it to be. If
we can only acquire the habit of attending
to our sensations, we may know theih per-
fectly. But how are the sensations of the
mind produced by impressions upon the
body ? Of this we are absolutely iguorant,
having no means of knowing how the body
acts upon the mind, or the mind upon the
body. When we consider the nature and
attributes of both, they seem to be so differ-
ent, and so unlike, that we can find no handle
by which the one may lay hold of the other.
There is a deep and a dark gulf between
them, which our understanding cannot pass ;
and the manner of their correspondence and
intercourse is absolutely unknown.

Experience teaches us, that certain im-
pressions upon the body are constantly fol-

lowed by certain sensations of the mind ;
and that, on the other hand, certain deter-
minations of the mind are constantly fol-
lowed by certain motions in the body ; but
we see not the chain that ties these things
together. Who knows but their connection
may be arbitrary, and owing to the will of
our Maker ? Perhaps the same sensations
might have been connected with other im-
pressions, or other bodily organs. Perhaps
we might have been so made as to taste with
our fingers, to smell with our ears, and to
hear by the nose. Perhaps we might have
been so made as to have all the sensations
and perceptions which we have, without any
impression made upon our bodily organs at

However these things may be, if. Nature
had given us nothing more than impressions
made upon the body, and sensations in our
minds corresponding to them, we should, in
that case, have been merely sentient, but not
percipient beings. We should never have
been able to form a conception of any ex-
ternal object, far less a belief of its exist-
ence. Our sensations have no resemblance
to external objects ; nor can we discover,
by our reason, any necessary connection
between the existence of the former, and
that of the latter.

We might, perhaps, have been made of
such a constitution as to have our present
perceptions connected with other sensations.
We might, perhaps, have had the percep-
tion of external objects, without either im-
pressions upon the organs of sense, or sens-
ations. Or, lastly, The perceptions we have,
might have been immediately connected
with the impressions upon our organs, with-
out any intervention of sensations. This
last seems really to be the case in one in-
stance — to wit, in our perception of the
visible figure of bodies, as was observed in
the eighth section of this chapter.

The process of Nature, in perception by
the'senses, may, therefore, be conceived as a
kind of drama, wherein some things are per-
formed behind the scenes, others are repre-
sented to the mind in different scenes, one
succeeding another. The impression made
by the object upon the organ, either by im-
mediate contact or by some intervening
medium, as well as the impression made
upon the nerves and brain, is performed
behind the scenes, and the mind sees nothing
of it. But every such impression, by the
laws of the drama, is followed by a sensa-
tion, which is the first scene exhibited to
the mind ; and this scene is quickly suc-
ceeded* by another, which is the percep-
tion of the object.

In this drama, Nature is the actor, we
are the spectators. We know nothing of

• See the preceding note.— H.



the machinery by means of which every
different impression upon the organ, nerves,
and brain, exhibits its corresponding sens-
ation; or of the machinery by means of
which each sensation exhibits its corre-
sponding perception. We are inspired with
the sensation, and we are inspired with the
corresponding perception, by means un-
known.* And, because the mind passes
immediately from the sensation to that con-
ception and belief of the object which we
have in perception, in the same manner as
it passes from signs to the things signified
by them, we have, therefore, called our
sensations signs of external objects ; finding
no word more proper to express the func-
tion which Nature hath assigned them in
perception, and the relation which they
bear to their corresponding objects.

There is no necessity of a resemblance
between the sign and the thing signified ;
and indeed no sensation can resemble any
external object. But there are two things
necessary to our knowing things by means
of signs. First, That a real connection
between the sign and thing signified be
established, either by the course of nature,
or by the will and appointment of men.
When they are connected by the course of
nature, it is a natural sign ; when by hu-
man appointment, it is an artificial sign.
Thus, smoke is a natural sign of fire ; cer-
tain features are natural signs of anger :
but our words, whether expressed by arti-
culate sounds or by writing, are artificial
signs of our thoughts and purposes.

Another requisite to our knowing things
by signs is, that the appearance of the sign
to the mind, be followed by the conception
and belief of the thing signified. Without
this, the sign isnot understood orinterpreted;
and, therefore, is no sign to us, however
fit in its own nature for that purpose.

Now, there are three ways in which the
mind passes from the appearance of a natu-
ral sign to the conception and belief of the
thing signified — by original principles of
our constitution, by custom, and by reason-

Our original perceptions are got in the
first of these ways, our acquired percep-
tions in the second, and all that reason dis-
covers of the course of nature, in the third.
In the first of these ways, Nature, by means
of the sensations of touch, informs us of the
hardness and softness of bodies ; of their
extension, figure, and motion ; and of that

space in which they move and are placed

as hath been already explained in the fifth
chapter of this inquiry. And, in the second
of these ways, she informs us, by means of
onr eyes, of almost all the same things

• On perception as a revelation — "a miraculous
revelatio»"_see Jacobi's 'vpavid Hume."— H.

which originally we could perceive only by

In order, therefore, to understand more
particularly how we learn to perceive so
many things by the eye, which originally
could be perceived only by touch, it will be
proper, First, To point out the signs by
which those things are exhibited to the eye,
and their connection with the things signi-
fied by them ; and, Secondly, To consider
how the experience of this connection pro-
duces that habit by which the mind, with-
out any reasoning or reflection, passes from
the sign to the conception and belief of the
thing signified.

Of all the acquired perceptions which we
have by sight, the most remarkable is the
perception of the distance of objects from
the eye ; we shall, therefore, particularly
consider the signs by which this perception
is exhibited, and only make some general
remarks with regard to the signs which are
used in other acquired perceptions.

Section XXII.


It was before observed in general, that
the original perceptions of sight are signs
which serve to introduce those that are
acquired ; but this is not to be understood
as if no other signs were employed, for that
purpose. There are several motions of the
eyes, which, in order to distinct vision,
must be varied, according as the object is
more or less distant ; and such motions be-
ing by habit connected with the correspond-
ing distances of the object, become signs of
those distances.* These motions were at
first voluntary and unconfined ; hut, as the
intention of nature was to produce perfect
and distinct vision by their means, we soon
learn by experience to regulate them accord-
ing to that intention only, without the least

A ship requires a different trim for every
variation of the direction and strength of
the wind ; and, if we may be allowed to
borrow that word, the eyes require a differ-
ent trim for every degree of light, and for
every variation of the distance of the object,
while it is within certain limits. The eyes
are trimmed for a particular object, by con-
tracting certain muscles and relaxing others;
as the ship is trimmed for a particular wind
by drawing certain ropes and slackening
others. The sailor learns the trim of his
ship, as we learn the trim of our eyes, by
experience. A ship, although the noblest
machine that human art can boast, is far

• See above, p. 182, note ».— H.



inferior to the eye in this respect, that it
requires art and ingenuity to navigate her ;
and a sailor must know what ropes he must
pull, and what he must slacken, to fit her
to a particular wind ; but with such superior
wisdom is the fabric of the eye, and the
principles of its motion contrived, that it
requires no art nor ingenuity to see by it.
Even that part of vision which is got by

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 43 of 114)