words, of the definite figure of bodies, is a _simple feeling_ of
touch, _immediate_, _original_, and _independent of time_; or is there
not rather reason to think, as I have endeavoured to show, that it is
a _compound_ feeling, of which _time_, that is to say, our notion of
succession, is an _original element_?
LECTURE XXV.
ON THE DISTINCTION BETWEEN SENSATION AND PERCEPTION,--AND BETWEEN THE
PRIMARY AND SECONDARY QUALITIES OF MATTER.
My last Lecture, Gentlemen, was chiefly employed in considering the
nature of that complex process which takes place in the mind, when
we ascribe the various classes of our sensations to their various
external objects,--to the analysis of which process we were led, by the
importance which Dr Reid has attached to the distinction of _sensation_
and _perception_;--a sensation, as understood by him, being the simple
feeling that immediately follows the action of an external body on any
of our organs of sense, considered merely as a feeling of the mind;
the corresponding perception being a reference of this feeling to the
external body as its cause.
The distinction I allowed to be a convenient one, if the nature of the
complex process which it expresses be rightly understood. The only
question that seemed, philosophically, of importance, with respect
to it, was, whether the _perception_ in this sense,--the reference
of the sensation to its external corporeal cause,--imply, as Dr Reid
contends, a peculiar mental power, coextensive with sensation, to be
distinguished by a peculiar name in the catalogue of our faculties,
or be not merely one of the results of a more general power, which is
afterwards to be considered by us,--the _power of association_,--by
which one feeling suggests, or induces, other feelings that have
formerly coexisted with it.
It would be needless to recapitulate the argument minutely, in its
relation to _all_ the senses. That of smell, which Dr Reid has himself
chosen as an example, will be sufficient for our retrospect.
Certain particles of odorous matter act on my nostrils,--a peculiar
_sensation_ of fragrance arises,--I refer this sensation to a rose.
This reference, which is unquestionably something superadded to the
original sensation itself, is what Dr Reid terms the perception of the
fragrant body. But what is the reference itself, and to what source
is it to be ascribed? That we should have supposed our sensations
to have had a cause of some sort, as we suppose a cause of all our
feelings internal as well as external, may indeed be admitted. But if
I had had no other sense than that of smell,--if I had never _seen_ a
rose,--or, rather, since the knowledge which vision affords is chiefly
of a secondary kind, if I had no mode of becoming acquainted with the
compound of extension and resistance, which the mere sensations of
smell, it is evident, are incapable of affording,--could I have made
this reference of my sensation to a quality of a fragrant body? Could
I, in short, have had more than the mere sensation itself, with that
general belief of a cause of some sort, which is not confined to our
sensations, but is common to them with all our other feelings?
By _mere smell_, as it appears to me, I could not have become
acquainted with the existence of corporeal substances,--in the sense
in which we now understand the term _corporeal_,--nor, consequently,
with the _qualities_ of corporeal substances; and, if so, how could
I have had that perception of which Dr Reid speaks,--that reference
to a fragrant body, of which, as a body, I was before in absolute
ignorance? I should, indeed, have ascribed the sensation to some
cause or antecedent, like every other feeling; but I could as little
have ascribed it to a bodily cause, as any feeling of joy or sorrow.
I refer it now to a _rose_; because, being endowed with _other_
sensitive capacities, I have previously learned, from another source,
the existence of causes without, extended and resisting,--because
I have previously touched or seen a rose, when the sensation of
fragrance coexisted with my visual or tactual sensation; and all
which distinguishes the _perception_ from the mere _sensation_, is
this suggestion of former experience, which reminds me now of other
feelings, with the continuance or cessation of which, in innumerable
former instances, the fragrance itself also continued or ceased.
The perception in short, in smell, taste, hearing, is a sensation
suggesting, by _association_, the notion of some extended and resisting
substance, fragrant, vapid, vibratory,--a notion which smell alone,
taste alone, hearing alone, never could have afforded; but which, when
once received from any other source, may be suggested by these as
readily as any other associate feeling that has frequently coexisted
with them. To the simple primary sensations of _vision_ the same remark
may be applied. A mere sensation of colour could not have made me
acquainted with the existence of bodies, that would resist my effort to
grasp them. It is only in one sense, therefore,--that which affords us
the knowledge of _resistance_,--that any thing like original perception
can be found; and even in this, the process of perception, as I
formerly explained to you, implies no peculiar power, but only common
sensations, with associations and inferences of precisely the same
kind, as those which are continually taking place in all our reasonings
and trains of thought.
_Extension_ and _resistance_, I need scarcely repeat, are the
complex elements of what we term matter; and nothing is matter to
our conception, or a body, to use the simpler synonymous term, which
does not involve these elements. If we had no other sense than that
of smell, and, therefore, could not have referred the sensations to
any fragrant body, what, in Dr Reid's meaning of this term, would the
supposed power of perception, in these circumstances, have been? What
would it have been, in like manner, if we had had only the sense of
taste in sweetness and bitterness,--or of hearing in melody,--or of
vision in colour,--without the capacity of knowing light as a material
substance, or the bodies that vibrated, or the bodies of another
kind that were sweet or bitter? It is only by the sense of touch,
or, at least, by that class of perceptions which Dr Reid ascribes to
touch,--and which, therefore, though traced by us, in part, to another
source, I, for brevity's sake, comprehend under that term in our
present discussion,--it is only by _touch_ that we become acquainted
with those elements which are essential to our very notion of a _body_;
and to touch, therefore, in his own view of it, we must be indebted,
directly or indirectly, as often as we refer the sensations of any
other class to a _corporeal_ cause. Even in the supposed perceptions of
touch itself, however, as we have seen, the reference of our feelings
to an external cause is not demonstrative of any peculiar power of
the mind, to be classed separately from its other faculties. But
when a body is first grasped, in infancy, by fingers that have been
accustomed to contract without being impeded, we learn to consider the
sensation as the result of a cause that is different from our own mind,
because it breaks an accustomed series of feelings, in which all the
antecedents, felt by us at the time, were such as were before uniformly
followed by a different consequent, and were expected, therefore, to
have again their usual consequent. The _cause_ of the new sensation,
which is thus believed to be something different from our sentient
self, is regarded by us as something which has parts, and which resists
our effort, that is to say, as an external body;--because the muscular
feeling, excited by the object grasped is, in the _first_ place,
the very feeling of that which we term resistance; and, _secondly_,
because, by uniformly supplying the place of a definite portion of a
progressive series of feelings, it becomes ultimately representative
of that particular length of series, or number of parts, of which it
thus uniformly supplies the place. Perception, then, even in that class
of feelings by which we learn to consider ourselves as surrounded by
substances extended and resisting, is only another name, as I have
said, for the result of certain associations and inferences that flow
from other more general principles of the mind; and with respect to all
our other sensations, it is only another name for the suggestion of
these very perceptions of touch, or at least of the feelings, tactual
and muscular, which are, by Dr Reid, ascribed to that single sense. If
we had been unsusceptible of these tactual and muscular feelings, and,
consequently, had never conceived the existence of any thing extended
and resisting till the sensation of fragrance, colour, sweetness, or
sound had arisen, we should, after any one or all of these sensations,
have still known as little of bodies without, as if no sensation
whatever had been excited.
The distinction, then, on which Dr Reid has founded so much, involves,
in his view of it, and in the view that is generally taken of it, a
false conception of the nature of the process which he describes.
The two words _sensation_ and _perception_, are, indeed, as I have
already remarked, very convenient for expressing, in one case, the mere
existence of an external feeling,--in the other case, the reference
which the percipient mind has made of this feeling to an external
cause. But this reference is all, which the perception superadds to
the sensation;--and the source of the reference itself we are still
left to seek, in the other principles of our intellectual nature. We
have no need, however, to invent a peculiar power of the mind for
producing it; since there are other principles of our nature, from
which it may readily be supposed to flow,--the principle by which we
are led to believe, that every new consequent, in a train of changes,
must have had a new antecedent of some sort in the train,--and the
principle of association, by which feelings, that have usually
coexisted, suggest or become representative of each other. With these
principles, it certainly is not wonderful, that when the fragrance
of a rose has uniformly affected our sense of smell, as often as the
flower itself was presented to us, we should ascribe the fragrance to
the flower which we have seen and handled;--but though it would not be
wonderful, that we should make it, it would indeed be wonderful, if,
with these principles, we did not make that very reference, for which
Dr Reid thinks it necessary to have recourse to a peculiar faculty of
perception.
Such, then, is the view, which I would take of that distinction of
_sensation_ and _perception_, which Dr Reid, and the philosophers
who have followed him, and many of philosophers, too, that preceded
him,--for the distinction, as I have said, is far from being an
original one,--have understood in a different sense; in consequence,
as I cannot but think, of a defective analysis of the mental process,
which constitutes the reference of our feelings of this class to
_causes_ that are _without_.
There is another distinction, which he has adopted from the
philosophers that preceded him, and which forms an important part of
his system of perception,--a distinction, that is just to a certain
extent,--though not to the full extent, and in the precise manner, in
which he and other writers have maintained;--and with respect to which,
therefore, it will be necessary to point out to you, how far I conceive
it to be safely admissible. I allude to the division, which has been
formed of the _primary_ and _secondary_ qualities of matter.
“Every one knows that extension, divisibility, figure, motion,
solidity, hardness, softness, and fluidity, were by Mr Locke called
primary qualities of body; and that sound, colour, taste, smell,
and heat or cold, were called secondary qualities. Is there a just
foundation for this distinction? Is there any thing common to the
primary, which belongs not to the secondary? And what is it?
“I answer, that there appears to me to be a real foundation for the
distinction; and it is this: That our senses give us a direct and a
distinct notion of the primary qualities, and inform us what they are
in themselves; but of the secondary qualities, our senses give us only
a relative and obscure notion. They inform us only, that they are
qualities that affect us in a certain manner, that is, produce in us a
certain sensation; but as to what they are in themselves, our senses
leave us in the dark.
“The notion we have of primary qualities is direct, and not relative
only. A relative notion of the thing, is, strictly speaking, no notion
of the thing at all, but only of some relation which it bears to
something else.
“Thus gravity sometimes signifies the tendency of bodies towards the
earth; sometimes it signifies the cause of that tendency: When it means
the first, I have a direct and distinct notion of gravity: I see it,
and feel it, and know perfectly what it is; but this tendency must have
a cause: We give the same name to the cause; and that cause has been an
object of thought and of speculation. Now what notion have we of this
cause, when we think and reason about it? It is evident, we think of it
as an unknown cause, of a known effect. This is a relative notion, and
it must be obscure; because it gives us no conception of what the thing
is, but of what relation it bears to something else. Every relation
which a thing unknown bears to something that is known, may give a
relative notion of it; and there are many objects of thought, and of
discourse, of which our faculties can give no better than a relative
notion.
“Having premised these things to explain what is meant by a relative
notion, it is evident, that our notion of primary qualities is not of
this kind; we know what they are, and not barely what relation they
bear to something else.
“It is otherwise with secondary qualities. If you ask me, what is that
quality or modification in a rose which I call its smell, I am at a
loss to answer directly. Upon reflection I find, that I have a distinct
notion of the sensation which it produces in my mind. But there can be
nothing like to this sensation in the rose, because it is insentient.
The quality in the rose is something which occasions the sensations
in me; but what that something is, I know not. My senses give me no
information upon this point. The only notion, therefore, my senses give
is this, That smell in the rose is an unknown quality or modification,
which is the cause or occasion of a sensation which I know well. The
relation which this unknown quality bears to the sensation with which
nature hath connected it, is all I learn from the sense of smelling;
but this is evidently a relative notion. The same reasoning will apply
to every secondary quality.
“Thus I think it appears, that there is a real foundation for the
distinction of primary from secondary qualities; and that they are
distinguished by this, that of the primary we have by our senses a
direct and distinct notion; but of the secondary only a relative
notion, which must, because it is only relative, be obscure; they are
conceived only as the unknown causes or occasions of certain sensations
with which we are well acquainted.”[92]
Though, as I have explained to you fully, in my former Lectures,
we should not,--at least in far the greater number of our
sensations,--have considered them, originally, as proceeding from
external causes, we yet, after the acquisitions of knowledge, with
which the first years of our life enrich us, believe, that there is
an external cause of all our sensations,--of smells and tastes, as
much as of those feelings of the mind, which constitute our notions
of extension and resistance. But the difference, in these cases,
is, that though we _learn_, by experience of certain successions
or co-existences of feelings, to refer to a _corporeal_ cause our
sensations of fragrance, and various other species of sensations,
there is nothing in the sensation of fragrance itself, or in the other
analogous sensations, of which I speak, that might not indicate as much
a cause directly spiritual, as a cause like that to which we at present
give the name of _body_,--while the very notion of extension and
resistance combined, seems necessarily to indicate a material cause, or
rather is truly that which constitutes our very notion of matter.
We believe, indeed, that our sensations of fragrance, sweetness, sound,
have causes of some sort, as truly as we believe, that our feelings
of extension and resistance have a cause, or causes of some sort; but
if we have previously given the name of matter, with direct reference
to the one set of effects, and not with direct reference to the other,
it necessarily follows, that, in relation to matter, as often as we
speak or think of it, the qualities which correspond with the one set
of effects, that have led us to use that name, must be regarded by us
as primary, and the others, which may, or may not coexist with these,
only as secondary. An external body may, or may not be fragrant,
because fragrance is not one of the qualities previously included by us
in our definition of a body; but it _must_ be _extended_, and present
an obstacle to our compressing force, because these are the very
qualities, which we have included in our definition, and without which,
therefore, the definition must cease to be applicable to the thing
defined.
If, originally, we had invented the word _matter_ to denote the cause,
whatever it might be, of our sensations of smell, it is very evident,
that _fragrance_ would then have been to us the primary quality of
_matter_, as being that which was essential to our definition of
matter,--and all other qualities, by which the cause of smell might,
or might not at the same time affect our other senses, would then have
been _secondary_ qualities only,--as being qualities compatible with
our definition of matter, but not essential to it.
What we now term matter, however, I have repeatedly observed,--is that
which we consider as _occupying space_, and _resisting our effort to
compress it_; and those qualities of matter may well be said to be
primary, by which matter itself, as thus defined, becomes known to
us,--or by the union of which, in our conception, we form the complex
notion of matter, and give or withhold that name according as these
qualities are present or absent. Extension and resistance are the
distinguishing qualities that direct us in all our applications of
the word which comprehends them. They are truly _primary_ qualities,
therefore; since, without our consideration of them, we never could
have formed the complex notion of the substance itself, to which we
afterwards, in our analysis of that complex notion, ascribe them
separately as qualities;--and all the other qualities, which we may
afterwards find occasion to refer to an extended resisting substance,
must evidently be secondary, in reference to those qualities, without
which as previously combined in our thought, we could not have had
the primary notion of the substance to which we thus secondarily refer
them. If, in the case which we have already frequently imagined, of the
single sense of smell, we had been absolutely unsusceptible of every
other external feeling, we might, indeed, have considered our sensation
as the effect of _some_ cause,--and even of a cause that was different
from our mind itself; but it is very evident that we could not have
considered it as the effect of the presence of _matter_, at least as
that term is now understood by us. If, in these circumstances,--after
frequent repetition of the fragrance, as the only quality of bodies
with which we could be acquainted,--we were to acquire in an instant
all the other senses which we now possess,--so as to become capable
of forming that complex notion of things extended and resisting,
which is our present notion of matter, we should then, indeed, have a
fuller notion of the rose, of the mere fragrance of which we before
were sensible, without knowing of what it was the fragrance, and might
learn to refer the fragrance to the rose, by the same coexistences of
sensations which have led us, in our present circumstances, to combine
the fragrance with other qualities, in the complex conception of the
flower. Even then, however, though the fragrance, which was our first
sensation, had truly been known to us before the other qualities, and
though the sensation, therefore, would deserve the name of primary,
the _reference_ of this earlier feeling to the external rose as its
cause, would still truly be _secondary_ to the earlier reference, or
rather to the earlier combination of other qualities, in one complex
whole, by which we had formed to ourselves the notion of the extended
and resisting rose, as a body, that admitted the subsequent reference
of the delightful sensation of fragrance to be made to it, as the equal
cause of these different effects.
In this sense, then, the distinction of the primary and secondary
qualities of matter is just,--that, whatever qualities we refer to a
_material_ cause must be, in reference, secondary to those qualities
that are essential to our very notion of the body, to which the
subsequent reference of the other qualities is made. We have formed our
definition of matter; and, as in every other definition of every sort,
the qualities included in the definition, must always, in comparison
of other qualities, be primary and essential, relatively to the thing
defined.
Nor is this all.--It will be admitted likewise, that the qualities
termed _primary_,--which alone are included in our general definitions
of matter, and which are all, as we have seen, modifications of mere
extension and resistance, are, even after we have learned to consider
the causes of all our sensations as substances external to the mind,
still felt by us to be external, with more clearness and vividness,
than the other qualities, which we term _secondary_. The difference
is partly, and chiefly, in the nature of the sensations themselves,
as already explained to you, but depends also, I conceive, in no
inconsiderable degree, on the permanence and universality of the
objects which possess the primary qualities, and the readiness with
which we can renew our feeling of them at will, from the constant
presence of our own bodily frame, itself extended and resisting, and of
the other causes of these feelings of extension and resistance, that
seem to be every where surrounding us. Tastes, smells, sounds,--even
colours though more lasting than these--are not always before us;--but
there is not a moment at which we cannot, by the mere stretching of
our hand, produce at pleasure, the feeling of something extended and
resisting. It is a very natural effect of this difference, that the one
set of causes which are always before us, should seem to us, therefore,
peculiarly permanent, and the other set, that are only occasionally
present, should seem almost as fugitive as our sensations themselves.