DEFINITION OF SENSATION
When making the analysis of matter we impliedly admitted two
propositions: first, that sensation is the _tertium quid_ which is
interposed between the excitant of our sensory nerves and ourselves;
secondly, that the aggregate of our sensations is all we can know of
the outer world, so that it is correct to define this last as the
collection of our present, past, and possible sensations. It is not
claimed that the outer world is nothing else than this, but it is
claimed with good reason that the outer world is nothing else _to us_.
It would be possible to draw from the above considerations a clear
definition of sensation, and especially it would be possible to decide
henceforth from the foregoing whether sensation is a physical or a
mental phenomenon, and whether it belongs to matter or to mind. This
is the important point, the one which we now state, and which we will
endeavour to resolve. To make the question clearer, we will begin it
afresh, as if it were new, and as if the facts hitherto analysed did
not already prejudge the solution. Let us begin by giving a definition
of sensation from the point of view of experimental psychology.
Sensation, then, is the phenomenon which is produced and which one
experiences when an excitant has just acted on one of our organs of
sense. This phenomenon is therefore composed of two parts: an action
exercised from outside by some body or other on our nervous substance;
and, then, the fact of feeling this action.
This fact of feeling, this state of consciousness, is necessary to
constitute sensation; when it does not exist, it is preferable to give
the phenomenon another name, otherwise the fault is committed of
mixing up separate facts. Physiologists have, on this point, some
faults of terminology with which to reproach themselves: for they have
employed the word sensibility with too little of the critical spirit.
Sensibility, being capacity for sensation, presupposes, like sensation
itself, consciousness. It has, therefore, been wrong, in physiology,
to speak of the sensibility of the tissues and organs, which, like the
vegetable tissues or the animal organs of vegetative life, properly
speaking, feel nothing, but react by rapid or slow movements to the
excitements they are made to receive. Reaction, by a movement or any
kind of modification, to an excitement, does not constitute a
sensation unless consciousness is joined with it, and, consequently,
it would be wiser to give unfelt excitements and reactions the name of
excitability.
The clearest examples of sensation are furnished by the study of man,
and are taken from cases where we perceive an external object. The
object produces upon us an action, and this action is felt; only, in
such cases, the fact of sensation comprises but a very small part of
the event. It only corresponds, by definition, to the actual action of
the object. Analysis after analysis has shown that we constantly
perceive far beyond this actual action of objects. Our mind, as we
say, outruns our senses. To our sensations, images come to attach
themselves which result from sensations anteriorly felt in analogous
circumstances. These images produce in us an illusion, and we take
them for sensations, so that we think we perceive something which is
but a remembrance or an idea; the reason being that our mind cannot
remain in action in the presence of a sensation, but unceasingly
labours to throw light upon it, to sound it, and to arrive at its
meaning, and consequently alters it by adding to it. This addition is
so constant, so unavoidable, that the existence of an isolated
sensation which should be perceived without the attachment of images,
without modification or interpretation, is well-nigh unrealisable in
the consciousness of an adult. It is a myth.
Let us, however, imagine this isolation to be possible, and that we
have before us a sensation free from any other element. What is this
sensation? Does it belong to the domain of physical or of moral
things? Is it a state of matter or of mind?
I can neither doubt nor dispute that sensation is, in part, a
psychological phenomenon, since I have admitted, by the very
definition I have given of it, that sensation implies consciousness.
We must, therefore, acknowledge those who define it as _a state of
consciousness_ to be right, but it would be more correct to call it
the _consciousness of a state_, and it is with regard to the nature of
this state that the question presents itself. It is only this state
which we will now take into consideration. It is understood that
sensation contains both an impression and a cognition. Let us leave
till later the study of the act of cognition, and deal with the
impression. Is this impression now of a physical or a mental nature?
Both the two opposing opinions have been upheld. In this there is
nothing astonishing, for in metaphysics one finds the expression of
every possible opinion. But a large, an immense majority of
philosophers has declared in favour of the psychological nature of the
impression. Without even making the above distinction between the
impression and the act of cognition, it has been admitted that the
entire sensation, taken _en bloc_, is a psychological phenomenon, a
modification of our consciousness and a peculiar state of our minds.
Descartes has even employed this very explicit formula: "The objects
we perceive are within our understanding." It is curious to see how
little trouble authors take to demonstrate this opinion; they declare
it to be self-evident, which is a convenient way of avoiding all
proof. John Stuart Mill has no hesitation in affirming that: "The
mind, in perceiving external objects, can only take notice of its own
conditions." And Renouvier expresses the same arbitrary assertion with
greater obscurity when he writes: "The monad is constituted by this
relation: the connection of the subject with the object within the
subject."[15] In other words, it is laid down as an uncontrovertible
principle that "the mental can only enter into direct relations with
the mental." That is what may be called "the principle of Idealism."
This principle seems to me very disputable, and it is to me an
astonishing thing that the most resolute of sceptics--Hume, for
example--should have accepted it without hesitation. I shall first
enunciate my personal opinion, then make known another which only
differs from mine by a difference of words, and finally I will discuss
a third opinion, which seems to me radically wrong.
My personal opinion is that sensation is of a mixed nature. It is
psychical in so far as it implies an act of consciousness, and
physical otherwise. The impression on which the act of cognition
operates, that impression which is directly produced by the excitant
of the nervous system, seems to me, without any doubt, to be of an
entirely physical nature. This opinion, which I make mine own, has
only been upheld by very few philosophers--Thomas Reid perhaps, and
William Hamilton for certain; but neither has perceived its deep-lying
consequences.
What are the arguments on which I rely? They are of different orders,
and are arguments of fact and arguments of logic. I shall first appeal
to the natural conviction of those who have never ventured into
metaphysics. So long as no endeavour has been made to demonstrate the
contrary to them, they believe, with a natural and naïve belief, that
matter is that which is seen, touched and felt, and that,
consequently, matter and our senses are confounded. They would be
greatly astonished to be informed that when we appear to perceive the
outer world, we simply perceive our ideas; that when we take the train
for Lyons we enter into one state of consciousness in order to attain
another state of consciousness.
Now, the adherents of this natural and naïve opinion have, as they say
in the law, the right of possession (_possession d'état_); they are
not plaintiffs but defendants; it is not for them to prove they are in
the right, it has to be proved against them that they are in the
wrong. Until this proof is forthcoming they have a presumption in
their favour.
Are we here making use of the argument of common opinion of mankind,
of which ancient philosophy made so evident an abuse? Yes, and no.
Yes, for we here adopt the general opinion. No, for we only adopt it
till the contrary be proved. But who can exhibit this proof to the
contrary? On a close examination of the question, it will be perceived
that sensation, taken as an object of cognition, becomes confused with
the properties of physical nature, and is identified with them, both
by its mode of apparition and by its content. By its mode of
apparition, sensation holds itself out as independent of us, for it is
at every instant an unexpected revelation, a source of fresh
cognitions, and it offers a development which takes place without and
in spite of our will; while its laws of co-existence and of succession
declare to us the order and march of the material universe. Besides,
by its content, sensation is confounded with matter. When a
philosopher seeks to represent to himself the properties of a material
object,--of a brain, for example--in order to contrast them with the
properties of a psychical activity, it is the properties of sensation
that he describes as material; and, in fact, it is by sensation, and
sensation alone, that we know these properties. Sensation is so little
distinct from them that it is an error to consider it as a means, a
process, an instrument for the knowledge of matter. All that we know
of matter is not known in or by sensation, but constitutes sensation
itself; it is not by the aid of sensation that we know colour; colour
is a sensation, and the same may be said of form, resistance, and the
whole series of the properties of matter. They are only our sensations
clothed with external bodies. It is therefore absolutely legitimate to
consider a part of our sensations, the object part, as being of
physical nature. This is the opinion to which I adhere.
We come to the second opinion we have formulated. It is, in appearance
at least, very different from the first. Its supporters agree that the
entire sensation, taken _en bloc_ and unanalysed, is to be termed a
psychological phenomenon. In this case, the act of consciousness,
included in the sensation, continues to represent a psychical element.
They suppose, besides, that the object on which this act operates is
psychical; and finally, they suppose that this object or this
impression was provoked in us by a physical reality which is kept in
concealment, which we do not perceive, and which remains unknowable.
This opinion is nowise absurd in itself: but let us examine its
consequences. If we admit this thesis, that sensations are
manifestations of mind which, although provoked by material causes,
are of a purely mental nature, we are forced to the conclusion that we
know none of the properties of material bodies, since we do not enter
into relations with these bodies. The object we apprehend by
perception is, according to this hypothesis, solely mental. To draw
therefrom any notion on material objects, it would have to be supposed
that, by some mysterious action, the mental which we know resembles
the physical which we do not know, that it retains the reflection of
it, or even that it allows its colour and form to pass, like a
transparent pellicle applied on the contour of bodies. Here are
hypotheses very odd in their realism. Unless we accept them, how is it
comprehensible that we can know anything whatever of physical nature?
We should be forced to acknowledge, following the example of several
philosophers, that the perception of the physical is an illusion.
As a compensation, that which this system takes from matter it
attributes to mind, which turns our familiar conceptions upside down.
The qualities of sensation detached from matter will, when applied to
mind, change its physiognomy. There are sensations of extent, weight,
space, and form. If these sensations are turned into psychical events,
we shall have to grant to these events, to these manifestations of the
mind, the properties of extent, of weight, of form. We shall have to
say that mind is a resisting thing, and that it has colour.
It may be said that this fantasy of language is not very serious. So
be it. But then what remains of the dualism of mind and matter? It is
at least singularly compromised. We may continue to suppose that
matter exists, and even that it is matter which provokes in our mind
those events which we call our sensations; but we cannot know if by
its nature, its essence, this matter differs from that of mind, since
we shall be ignorant of all its properties. Our ignorance on this
point will be so complete that we shall not even be able to know
whether any state which we call mental may not be physical. The
distinction between physical and mental will have lost its _raison
d'être_, since the existence of the physical is necessary to give a
meaning to the existence of the mental. We are brought, whether we
like it or not, to an experimental monism, which is neither psychical
nor physical; panpsychism and panmaterialism will have the same
meaning.[16]
But this monism can be only transitory, for it is more in the words
than in the thing itself. It is brought about by the terminology
adopted, by the resolution to call mental all the phenomena that it is
possible to know. Luckily, our speculations are not at the mercy of
such trifling details as the details of language. Whatever names may
be given to this or that, it will remain none the less true that
nature will continue to present to us a contrast between phenomena
which are flints, pieces of iron, clods of earth, brains--and some
other phenomena which we call states of consciousness. Whatever be the
value of this dualism, it will have to be discussed even in the
hypothesis of panpsychism.[17] As for myself, I shall also continue to
make a distinction between what I have called objects of cognition and
acts of cognition, because this is the most general distinction that
can be traced in the immense field of our cognitions. There is no
other which succeeds, to the same degree, in dividing this field into
two, moreover, this distinction is derived directly from observation,
and does not depend for its validity on the physical or mental nature
of the objects. Here is, then, a duality, and this duality, even when
it does not bear the names physical and moral, should necessarily play
the same part, since it corresponds to the same distinction of fact.
In the end, nothing will be changed, and this second opinion must
gradually merge into the one first stated by me, and of which I take
the responsibility. We may, therefore, put it out of consideration.
I have mentioned a third opinion, stating that it appeared to me to be
radically false. Outwardly it is the same as the last; looked at
superficially it seems even confused with it; but, in reality it is of
a totally different nature. It supposes that sensation is an entirely
psychological phenomenon. Then, having laid down this thesis, it
undertakes to demonstrate it by asserting that sensation differs from
the physical fact, which amounts to supposing that we cannot know
anything but sensations, and that physical facts are known to us
directly and by another channel. This is where the contradiction comes
in. It is so apparent that one wonders how it has been overlooked by
so many excellent minds. In order to remove it, it will be sufficient
to recollect that we do not know anything other than sensations; it is
therefore impossible to make any distinction between the physical
object and the object of cognition contained in every sensation. The
line of demarcation between the physical and the moral cannot pass
this way, since it would separate facts which are identical.
We can, therefore, only deplore the error of all those who, to express
the difference between mind and matter, have sought a contrast between
sensation and physical facts. Physiologists, with hardly an exception,
have fallen into this error; when contemplating in imagination the
material working of the brain, they have thought that between the
movement of cerebral matter and sensation there was a gulf fixed. The
comparison, to have been correct, required to be presented in quite
another way. A parallel, for instance, should have been drawn between
a certain cerebral movement and the act of consciousness, and there
should have been said: "The cerebral motion is the physical
phenomenon, the act of consciousness the psychical." But this
distinction has not been made. It is sensation _en bloc_ which is
compared to the cerebral movement, as witness a few passages I will
quote as a matter of curiosity, which are borrowed from philosophers
and, especially, from physiologists.
While philosophers take as a principle of idealism, that the mental
can only know the mental, physiologists take, as a like principle,
the heterogeneity existing, or supposed to exist, between the nerve
impression and the sensation. "However much we may follow the
excitement through the whole length of the nerve," writes Lotze,[18]
"or cause it to change its form a thousand times and to metamorphose
itself into more and more delicate and subtle movements, we shall
never succeed in showing that a movement thus produced can, by its
very nature, cease to exist as movement and be reborn in the shape of
sensation...." It will be seen that it is on the opposition between
molecular movement and sensation, that Lotze insists. In like manner
Ferrier: "But how is it that the molecular modifications in the
cerebral cells coincide with the modifications of the consciousness;
how, for instance, do luminous vibrations falling upon the retina
excite the modification of consciousness called _visual sensation_?
These are problems we cannot solve. We may succeed in determining the
exact nature of the molecular changes which take place in the cerebral
cells when a sensation is felt, but this will not bring us an inch
nearer to the explanation of the fundamental nature of sensation."
Finally, Du Bois Reymond, in his famous discussion in 1880, on the
seven enigmas of the world, speaks somewhat as follows: "The
astronomical knowledge of the encephalon, that is, the most intimate
to which we can aspire, only reveals to us matter in motion. But no
arrangement nor motion of material particles can act as a bridge by
which we can cross over into the domain of intelligence.... What
imaginable link is there between certain movements of certain
molecules in my brain, on the one hand, and on the other hand
primitive, undefinable, undeniable facts such as: I have the sensation
of softness, I smell the odour of a rose, I hear the sound of an
organ, I see a red colour, &c...."
These three quotations show very conclusively that their authors
thought they could establish the heterogeneity of the two phenomena by
opposing matter to sensation. It must be recognised that they have
fallen into a singular error; for matter, whatever it may be, is for
us nothing but sensation; matter in motion, I have often repeated, is
only a quite special kind of sensation; the organic matter of the
brain, with its whirling movements of atoms, is only sensation.
Consequently, to oppose the molecular changes in the brain to the
sensation of red, blue, green, or to an undefined sensation of any
sort, is not crossing a gulf, and bringing together things which
cannot be compared, it is simply comparing one sensation to another
sensation.
There is evidently something equivocal in all this; and I pointed this
out when outlining and discussing the different theories of matter. It
consists in taking from among the whole body of sensations certain of
them which are considered to be special, and which are then invested
with the privilege of being more important than the rest and the
causes of all the others. This is about as illegitimate as to choose
among men a few individuals to whom is attributed the privilege of
commanding others by divine right. These privileged sensations which
belong to the sight, the touch, and the muscular sense, and which are
of large extent, are indeed extensive. They have been unduly
considered as objective and as representing matter because they are
better known and measurable, while the other sensations, the
unextensive sensations of the other senses, are considered as
subjective for the reasons that they are less known and less
measurable: and they are therefore looked on as connected with our
sensibility, our Ego, and are used to form the moral world.
We cannot subscribe to this way of establishing the contrast between
matter and thought, since it is simply a contrast between two
categories of sensations, and I have already asserted that the
partitioning-out of sensations into two groups having different
objective values, is arbitrary.
FOOTNOTES:
[Footnote 15: CH. RENOUVIER et L. PRAT, _La Nouvelle Monadologie_, p.
148.]
[Footnote 16: An American author, MORTON PRINCE, lately remarked this:
_Philosophical Review_, July 1904, p. 450.]
[Footnote 17: This FLOURNOY recently has shown very wittily. See in
_Arch. de Psychol._, Nov. 1904, his article on Panpsychism.]
[Footnote 18: This extract, together with the two subsequent, are
borrowed from an excellent lecture by FLOURNOY, on _Métaphysique et
Physiologie_. Georg: Geneva, 1890.]