Thomas Reid.

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

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our observation. And we can then only
allow some weight to thisargumeut in favour
of hypotheses, when it can be shewn that
the cause of any one phenomenon in nature
has been, or can be found, as an unknown
quantity is, by the rule of false, or by alge-
braical analysis. This, I apprehend, will
never be, till the tera arrives, which Dr
Hartley seems to foretell, " When future
generations shall put all kinds of evidences
and enquiries into mathematical forms ;
and, as it were, reduce Aristotle's ten Ca-
tegories, and Bishop Wilkin's forty Summit
Uetiera to the head of quantity alone, so as
[89, 90]

to make mathematics and logic, natural
history and civil history, natural philoso-
phy and philosophy of all other kinds,
coincide owni ex parte."

Since Sir Isaac Newton laid down the
rules of philosophising in our inquiries into
the works of Nature, many philosophers
have deviated from them in practice ; per-
haps few have paid that regard to them
which they deserve. But they have met
with very general approbation, as being
founded in reason, and pointing out the
only path to the knowledge of Nature's
works. Dr Hartley is the only author I
have met with who reasons against them,
and has taken pains to find out arguments
in defence of the exploded method of hy-
pothesis. [90]

Another condition which Sir Isaac New-
ton requires in the causes of natural things
assigned by philosophers, is, that they be
sufficient to account for the phaanomena.
Vibrations, and vibratiuncles of the me-
dullary substance of the nerves and brain,
are assigned by Dr Hartley to account W
all our sensations and ideas, and, in a word,
for all the operations of our minds. Let
us consider very briefly how far they are
sufficient for that purpose.

It would be injustice to this author to
conceive him a materialist. He proposes
his sentiments with great candour, and they
ought not to be carried beyond what his
words express. He thinks it a consequence
of his theory, that ■ matter, if it can be
endued with the most simple kinds of sens-
ation, might arrive at all that intelligence
of which the human mind is possessed.
He thinks that his theory overturns all
the arguments that are usually brought for
the immateriality of the soul, from the
subtilty of the internal senses, and of the
rational faculty ; but he does not take upon
him to determine whether matter can be
endued with sensation or no. He even
acknowledges that matter and motion,
however subtilly divided and reasoned upon,
yield nothing more than matter and motion
still ; and therefore he would not be any
way interpreted so as to oppose the imma-
teriality of the soul.

It would, therefore, be unreasonable to
require that his theory of vibrations should,
in the proper sense, account for our sensa-
tions. It would, indeed, be ridiculous in
any man to pretend that thought of any kind
must necessarily result from motion, or
that vibrations in the nerves must neces-
sarily produce thought, any more than the
vibrations of ,a pendulum. Dr Hartley
disclaims this way of thinking, and there-
fore it ought not to be imputed to him.
All that he pretends is, that, in the human
constitution, there is a certain connection
between vibrations in the medullary sub-



Qessat II.

stance of the nerves and brain, and the
thoughts of the mind ; so that the last de-
pend entirely upon the first, and every kind
of thought [91] in the mind arises in conse-
quence of a corresponding vibration, or
vibratiuncle in the nerves and brain. Our
sensations arise from vibrations, and our
ideas from vibratiuncles, or miniature vibra-
tions ; and he comprehends, under these
two words of sensations and ideas, all the
operations of the mind.

But how can we expect any proof of the
connection between vibrations and thought,
when the existence of such vibrations was
never proved ? The proof of their connec-
tion cannot be stronger than the proof of
their existence ; for, as the author acknow-
ledges that we cannot infer the existence
of the thoughts from the existence of the
vibrations, it is no less evident that we can-
not infer the existence of vibrations from
the existence of our thoughts. The exist-
ence of both must be known before we can
know their connection. As to the exist-
ence of our thoughts, we have the evidence
of consciousness, a kind of evidence that
never was called in question. But as to
the existence of vibrations in the medullary
substance of the nerves and brain, no proof
has yeFbeen brought.

All, therefore, we have to expect from
this hypothesis, is, that in vibrations, con-
sidered abstractly, there should be a variety
in kind and degree, which tallies so exactly
with the varieties of the thoughts they are to
account for, as may lead us to suspect some
connection between the one and the other.
If the divisions and subdivisions of thought
be found to run parallel with the divisions
and subdivisions of vibrations, this would
give that kind of plausibility to the hypo-
thesis of their connection, which we com-
monly expect even in a. mere hypothesis ;
but we do not find even this.

For, to omit all those thoughts and oper-
ations which the author comprehends under
the name of ideas, and which he thinks arc
connected with vibratiuncles ; to omit the
perception of external objects, which he
comprehends under the name of sensations ;
to omit the sensations, properly so called,
which accompany our passions [92] and
affections, and to confine ourselves to the
sensations which we have by means of our
external senses, we can perceive no corre-
spondence between the variety we find in
their kinds and degrees, and that which may
be supposed in vibrations. .

We have five senses, whose sensations
differ totally in kind. By each of these,
excepting perhaps that of hearing, we have
a variety of sensations, which differ specific-
ally, and not in degree only. How many
tastes and smells are there which are spe-
fically differeut, each of them capable of all

degrees of strength and weakness ? Heat
and cold, roughness and smoothness, hard-
ness and softness, pain and pleasure, are
sensations of touch that differ in kind, and
each has an endless variety of degrees.
Sounds have the qualities of acute and
grave, loud and low, with all different de-
grees of each. The varieties of colour are
many more than we have names to express.
How shall we find varieties in vibrations
corresponding to all this variety of sensa-
tions which we have by our five senses
only ?

I know two qualities of vibrations in an
uniform elastic medium, and I know no
more. They may be quick or slow in vari-
ous degrees, and they may be strong or
weak in various degrees ; but I cannot find
any division of our sensations that will make
them tally with those divisions of vibra-
tions. If we had no other sensations but
those of hearing, the theory would answer
well; for sounds are either acute or grave,
which may answer to quick or slow vibra-
tions ; or they are loud or low, which an-
swer to strong or weak vibrations. But
then we have no variety of vibratious cor-
responding to the immense variety of sens-
ations which we have by sight, smell, taste,
and touch.

Dr Hartley has endeavoured to find out
other two qualities of vibrations ; to wit,
that they may primarily affect one part of
the brain or another, and that they may
vary in their direction according as they
enter by different external nerves ; but these
[93] seem to be added to make a number;
for, as far as we know, vibrations in an
uniform elastic substance spread over the
whole, and in all directions. However,
that we may be liberal, we shall grant him
four different kinds of vibrations, each of
them having as many degrees as he pleases.
Can he, or any man, reduce all our sensa-
tions to four kinds ? We have five senses,
and by each of them a variety of sensations,
more than sufficient to exhaust all the
varieties we are able to conceive in vibra-

Dr Hartley, indeed, was sensible of the
difficulty of finding vibrations to suit all the
variety of our sensations. His extensive
knowledge of physiology and pathology
could yield him but a feeble aid ; and, there-
fore, he is often reduced to the necessity of
heaping supposition upon supposition, con-
jecture upon conjecture, to give some credi-
bility to his hypothesis ; and, in seeking out
vibrations which may correspond with the
sensations of one sense, he seems to forget
that those must be omitted which have been
appropriated to another.

Philosophers have accounted in some de-
gree for our various sensations of sound by
the vibrations of elastic air; but it is to be





observed, first, That we know that such vi-
brations do really exist ; and, secondly, That
they tally exactly with the most remarkable
phenomena of sound. We cannot, indeed,
shew how any vibration should produce the
sensation of sound. This must be resolved
into the will of God, or into some cause
altogether unknown. But we know that,
as the vibration is strong or weak, the
sound is loud or low ; we know that, as the
vibration is quick or slow, the sound is
acute or grave. We can point out that
relation of synchronous vibrations which
produces harmony or discord, and that
relation of successive vibrations which pro-
duces melody ; and all this is not conjec-
tured, but proved by a sufficient induction.
This account of sounds, therefore, is philo-
sophical : although, perhaps, there may be
many things relating to sound that we can-
not account for, and of which the causes
remain latent. The connections described
[94] in this branch of philosophy are the
work of Gou, and not the fancy of men.

If anything similar to this could be shewn
in accounting for all our sensations by
vibrations in the medullary substance of the
nerves and brain, it would deserve a place
in sound philosophy ; but, when we are told
of vibrations in a substance which no man
could ever prove to have vibrations, or to
be capable of them ; when such imaginary
vibrations are brought to account for all our
sensations, though we can perceive no cor-
respondence in their variety of kind and
degree to the variety of sensations — the con-
nections described in such a system are the
creatures of human imagination, not the
work of God.

The rays of light make an impression
upon the optic nerves ; but they make none
upon the auditory or olfactory. The vibra-
tions of the air make an impression upon
the auditory nerves ; but none upon the
optic or the olfactory. The effluvia of
bodies make an impression upon the olfac-
tory nerves ; but make none upon the optic
or auditory. No man has been able to give
a shadow of reason for this. While this is
the case, is it not better to confess our
ignorance of the nature of those impressions
made upon the nerves and brain in percep-
tion, than to flatter our pride with the con-
ceit of knowledge which we have not, and
to adulterate philosophy with the spurious
brood of hypotheses ?*

* Reid appears to have been unacquainted with
the works and theory of Bonnet. — With our author's
strictures on the physiological hypotheses, the reader
may compare those of Tetens, in his " Versuche."
and of Stewart in his " Philosophical Essays." — H,

f°4, 95]



Some philosophers among the ancients,
as well as among the moderns, imagined
that man is nothing but a piece of matter,
so curiously organized that the impressions
of external objects produce in it sensation,
perception, remembrance, and all the other
operations [95] we are conscious of.* This
foolish opinion could only take its rise from
observing the constant connection which
the Author of Nature hath established be-
tween certain impressions made upon our
senses and our perception of the objects by
which the impression is made ; from which
they weakly inferred that those impressions
were the proper efficient causes of the cor-
responding perception.

But no reasoning is more fallacious than
this — that, because two things are always
conjoined, therefore one must be the cause
of the other. Day and night have been
joined in a constant succession since the
beginningof the world; but who is so foolish
as to conclude from this that day is the
cause of night, or night the cause of the
following day ? There is indeed nothing
more ridiculous than to imagine that any
motion or modification of matter should pro-
duce thought.

If one should tell of a telescope so exactly
made as to have the power of seeing ; of a
whispering gallery that had the power of
hearing ; of a cabinet so nicely framed as to
have the power of memory ; or of a machine
so delicate as to feel pain when it was
touched — such absurdities are so shocking to
common sense that they would not find belief
even among savages; yet it is the same
absurdity to think that the impressions of
external objects upon the machine of our
bodies can be the real efficient cause of
thought and perception.

Passing this, therefore, as a notion too
absurd to admit of reasoning, another con-
clusion very generally made by philoso-
phers is, that, in perception, an impression
is made upon the mind as well as upon the
organ, nerves, and brain. Aristotle, as
was before observed, thought that the form
or image of the object perceived, enters by

* The Stoics are leprehended for such a doctrine
by Boethius: —

•' Quondam porticus attulit

Obscuros nimiuro sencs,

Qui sensus ct imagines

E corporibus extunis

Credant mentibus imprimi,

LH quf.mtam celeri stylo

Mos est aequore pagina?

Quae uullas habeat notas,

Piessas figere Iiteras." &c
The tabula rasa remounts, however, to Arisujtb
— indeed to Plato— as an illustration. — H.




the organ of sense, and strikes upon the
mind.* Mr Hume gives the name of im-
pressions to all our perceptions, to all our
sensations, and even to the objects which
we perceive. Mr Locke affirms very posi-
tively, that the ideas of external objects are
produced [96] in our minds by impulse,
" that being the only way we can conceive
bodies to operate in." It ought, however, to
be observed, in justice to Mr Locke, that he
retracted this notion in his first letter to the
Bishop of Worcester, and promised, in the
next edition of his Essay, to have that pas-
sage rectified ; but, either from forgetful-
ness in the author, or negligence in the
printer, the passage remains in all the sub-
sequent editions I have seen.

There is no prejudice more natural to
man than to conceive of the mind as hav-
ing some similitude to body in its opera-
tions. Hence men have been prone to
imagine that, as bodies are put in motion
by some impulse or impression made upon
them by contiguous bodies, so the mind is
made to think and to perceive by some im-
pression made upon it, or some impulse
given to it by contiguous objects. If we
have such a notion of the mind as Homer
had of his gods — who might be bruised or
wounded with swords and spears— we may
then understand what is meant by impres-
sions made upon it by a body ; but, if we
conceive the mind to be immaterial — of
which I think we have very strong proofs —
we shall find it difficult to affix a meaning
to impressions made upon it.

There is a figurative meaning of impres-
sions on the mind which is well authorized,
and of which we took notice in the observa-
tions made on that word ; but this meaning
applies only to objects that are interesting.
To say that an object which I see with per-
fect indifference makes an impression upon
my mind, is not, as I apprehend, good
English. If philosophers mean no more
but that I see the object, why should they
invent an improper phrase to express what
every man knows how to express in plain
English ?

But it is evident, from the manner in
which this phrase is used by modern philo-
sophers, that they mean, not barely to ex-
press by it my perceiving an object, but to
explain the manner of perception. They
think that the object perceived acts upon
the mind in some way similar to that in
which one body acts upon another, by
making [97] an impression upon it. The
impression upon the mind is conceived to
be something wherein the mind is alto-
gether passive, and has some effect pro-

• A mere metaphor in Aristotle. (See Notes K
and M.) At any rate, the imprr esion was supposed
tn be made nn the animated sensor}, and not on the
intellrct — H.

duced in it by the object. But this is a
hypothesis which contradicts the common
sense of mankind, and which ought not to
be admitted without proof.

When I look upon the wall of my room,
the wall does not act at all, nor is capable
of acting ; the perceiving it is an act or
operation in me. That this is the common
apprehension of mankind with regard to
perception, is evident from the manner of
expressing it in all languages.

The vulgar give themselves no trouble
how they perceive objects — they express
what they are conscious of, and they express
it with propriety ; but philosophers have an
avidity to know how we perceive objects ;
and, conceiving some shnilitude between a
body that is put in motion, and a mind that
is made to perceive, they are led to think
that, as the body must receive some impulse
to make it move, so the mind must receive
some impulse or impression to make it per-
ceive. This analogy seems to be confirmed,
by observing that we perceive objects only
when they make some impression upon the
organs of sense, and upon the nerves and
brain ; but it ought to be observed, that
such is the nature of body that it cannot
change its state, but by some force impressed
upon it. This is not the nature of mind.
All that we know about it shews it to be in
its nature living and active, and to have
the power of perception in its constitution,
but still within those limits to which it is
confined by the laws of Nature.

It appears, therefore, that this phrase of
the mind's having impressions made upon
it by corporeal objects in perception, is
either a phrase without any distinct mean-
ing, and contrary to the propriety of the
English language, or it is grounded upon
an hypothesis which is destitute of proof.
On that account, though we grant that in
perception there is an impression made
upon the organ of [98] sense, and upon the
nerves and brain, we do not admit that
the object makes any impression upon the

There is another conclusion drawn from
the impressions made upon the brain in
perception, which I conceive to have no
solid foundation, though it has been adopted
very generally by philosophers. It is, that,
by the impressions made on the brain,
images are formed of the object perceived ;
and that the mind, being seated in the brain
as its chamber of presence, immediately
perceives those images only, and has no
perception of the external object but by
them. This notion of our perceiving ex-
ternal objects, not immediately, but in cer-
tain images or species of them conveyed by
the senses, seems to be the most ancient
philosophical hypothesis we have on the
subject of perception, and to have with





small variations retained its authority to
this day.

Aristotle, as was before observed, main-
tained, that the species, images, or forms
of external objects, coming from the object,
are impressed on the mind. The followers
of Democritus and Epicurus held the same
thing, with regard to slender films of sub-
tile matter coming from the object, that
Aristotle did with regard to his immaterial
species or forms.

Aristotle thought every object of human
understanding enters at first by the senses ;•
and that the notions got by them are by
the powers of the mind refined and spirit-
ualized, so as at last to become objects of
the most sublime and abstracted sciences.
Plato, on the other hand, had a very mean
opinion of all the knowledge we get by the
senses. He thought it did not des'erve the
name of knowledge, and could not be the
foundation of science ; because the objects
of sense are individuals only, 'and are in a
constant fluctuation. All science, according
to him, must be employed about those
eternal and immutable ideas which existed
before the objects of sense, and are not liable
to any change. In this there was an essen-
tial difference between the systems of these
two philosophers. [99] The notion of eter-
nal and immutable ideas, which Plato bor-
rowed from the Pythagorean school, was
totally rejected by Aristotle, who held it as
a maxim, that there is nothing in the intel-
lect, which was not at first in the senses.

But, notwithstanding this great difference
in those two ancient systems, they might
both agree as to the manner in which we
perceive objects by our senses : and that
they did so, I think, is probable ; because
Aristotle, as far as I know, neither takes
notice of any difference between himself
and his master upon this point, nor lays
claim to his theory of the manner of our
perceiving objects as his own invention.
It is still more probable, from the hints
which Plato gives in the seventh book of his
Republic, concerning the manner in which
we perceive the objects of sense ; which he
compares to persons in a deep and dark cave,
who see not external objects themselves but
only their shadows, by a light let into the
cave through a small opening, -f

It seems, therefore, probable that the Py-
thagoreans and Platonists agreed with the
Peripatetics in this general theory of per-
ception—to wit, that the objects of sense

* This is a very doubtful point, and has accord-
ingly divided his followers. Texts can be quoted to
prove, on the one side, that Aristotle-derived all our
notions, a posteriori, from the experience of sense ;
and, on the other, that he viewed sense only as afford,
ing to intellect the condition requisite for it to bo-
come actually conscious of the native and necessary
notions it, a priori, virtually possessed. — H.

+ Reid wholly mistakes the meaning of Plato's
simile of the cave. See below, under p. 1 16. — H.
[.99, 100]

are perceived only by certain images, or
shadows of them, let into the mind, as into
a camera obscura. •

The notions of the ancients were very
various with regard to the seat of the soul
Since it has been discovered, by the im-
provements in anatomy, that the nerves
are the instruments of perception, and of
the sensations accompanying it, and that
the nerves ultimately terminate in the
brain,-)- it has been the general opinion of
philosophers that the brain is the seat uf
the soul ; and that she perceives the images
that are brought there, and external things,
only by means of them.

Des Cartes, observing that the pineal
gland is the only part of the brain that is
single, all the other parts being double,^
and thinking that the soul must have one
seat, was determined by this [100] to make
that gland the soul's habitation, to which,
by means of the animal spirits, intelligence
is brought of all objects that affect the
senses. §

Others have not thought proper to con-
fine the habitation of the soul to the pineal
gland, but to the brain in general, or to
some part of it, which they call the sen-
sorium. Even the great Newton favoured
this opinion, though he proposes it only as
a query, with that modesty which dis-
tinguished him no less than his great genius.
"Is not," says he, " the sensorium of animals
the place where the sentient substance is
present, and to which the sensible species of
things are brought through the nerves and
brain, that there they may be perceived by
the mind present in that place ? And is
there not an incorporeal, living, intelligent,
and omnipresent Being, who, in infinite
space, as if it were in his sensorium, inti-
mately perceives things themselves, and
comprehends them perfectly, as being pre-
sent to them ; of which things, that prin-
ciple in us, which perceives and thinks,
discerns only, in its little sensorium, the
images brought to it through the organs of
the senses ?"||

His great friend Dr Samuel Clarke
adopted the same sentiment with more con-
fidence. In his papers to Leibnitz, we
find the following passages : " Without
being present to the images of the things
perceived, it (the soul) could not possibly
perceive them. A lfviiig substanee can
only there perceive where it is present,

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 57 of 114)