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 FACTSANDMENTALSYMBOLS.
IPERCEIVE from Dr. Carus's answer to my letter in No. 3
Vol. I of The Monist, that amid all the agreement of our mutual
endeavors a material difference of exists between us on an
opinion

important of special character. As I was not successful in

question

rendering my thought clear on this point, I shall endeavor on the

present occasion to explain what itwas that forced me to abandon

my old position (1863), which is very near to that of Dr. Carus, and
to assume a new one. The that our difference of opin
supposition
ion is merely and can be a
apparent adjusted by precise agreement
as to the terms employed is a very natural one in philosophical dis
cussions. It is hardly tenable, though, when the divergent views
in question arise subsequently to one another in the same person.

I must state, in starting, that I pursued

inmy youth physical
and philosophical studies, particularly psychology, with equal ardor.
There was hardly the question at that time of an experimental psy

chology, of a relation of psychological to physiological research.

No more so did physics at that day think of a psychological analysis
of the notions itwas constantly employing. How the notions of

"matter," "atom," etc., were come was not investi

"body," by,

gated. Objects were given of which physicists never questioned

the inviolability and with which they unconcernedly pursued their
labors.

The fields of physical and psychological research thus stood un~

conciliated the one by the side of the other, each having its own par
ticular concepts, methods, and theories. No one questioned, in
 FACTS AND MENTAL SYMBOLS. I99

deed, that the two were connected in some way. The

departments

way, however, appeared an insoluble riddle ; as it yet appears to

Dubois-Reymond.

although this condition of things was not such as to satisfy

Now

my mind, it was nevertheless natural that as a student I should

seek to acquire tentatively the prevailing views of both provinces
and them into consistent connection with one another.
put
I thus formed provisorily the view that Nature has two sides?
a physical and a psychological If psychical life is to be har
side.
monised at all with the theories of physics we are obliged, I thought,
to conceive of the atoms as feeling (ensouled). The various dynamic

phenomena of the atoms would then represent the physical pro

cesses, while the internal states connected therewith would be the
phenomena of psychic life. If we accept in faith and seriousness
the atomistic speculations of the physicists and of the early psychol

ogists (on the unity of the soul), I still see hardly any other course
to arrive at a half-way supportable monistic conception.
It is unnecessary to set forth at length here what a prominent

place the artificial scaffolding we employ in the construction of

our assumes in these monadic theories as contradistin
knowledge

guished from the facts that deserve knowledge, and how poorly such
theories satisfy in the long run a vigorous mind. As a fact, em
with this cumbrous artifice was in my case the means that
ployment
effected very soon the appearance of my better conviction, already

latently present.*

* A Greek to whom change of spatial configuration,

philosopher pressure, and
were probably the only natural processes of which he had any intimate
percussion
knowledge, thought out the atomistic theory. This theory we retain to-day, though
it be in a modified form. And in fact natural phenomena really do exist that act
as if the pressure and impact of very small particles were involved in their produc
tion (the dynamical theory of gases), phenomena that admit therefore by this con

ception of being more clearly viewed. However, this conception, like that of
calorie^
possesses value only in certain fields. We know to-day that pressure and impact
are by no means simpler phenomena than are for example the phenomena of gravi
tation. Thecontention that in physics everything can be reduced to the motion of
smallest particles is, taken at its best, a more than improper draft on the future.
Utterances of this kind afford no assistance to the solution of burning special ques

tions, but only confound, and have about the same explanatory value as the utter
ances of the late ph)'sical philosophy of Oken which prescribe for example with the
200 THE MONIST.

In the further progress of my physical work I soon discovered

that itwas very necessary sharply to distinguish between what we see
and what we mentally supply. When, for example, I imagine heat
as a substance (a fluid) that passes from one body into another, I
follow with ease the of conduction and
phenomena compensation.
This idea led Black, who established it, to the discovery of specific
heat, of the latent heat of fusion and vaporisation, and so forth.
This same idea of a constant of heat-substance on
quantity prevented
the other hand Black's successors They from using their eyes. no

longer mark every savage knows, that heat isproduced

the factwhich

by friction. By the help of his undulatory theory Huygens follows

with ease the phenomena of the reflexion and refraction of light.
The same theory prevents him, for he thinks solely of the longitud
inal waves with which he was familiar, from marking the fact of

polarisation which he himself discovered, but which Newton on

the other hand, undisturbed by theories, perceives at once. The

conception of fluids acting at a distance on conductors charged with

electricity facilitates our view of the behavior of the objects charged,

but it stood in the ivay of the discovery of the specific inductive ca

pacity, which was reserved for the eye of Faraday undimmed by

any traditional theories.

a division of zero-quantities
greatest ease the course of the creation of the world by
into + a and ? a (o= 4- a ? a).
The motion of a single body as a totality does indeed appear simpler at first

glance than any other process, and this is the justification of attempts at a physical
monadic theory. The thoughts of a single man are connected together ; the thoughts
of two different men are not. How can the processes of the different parts of the
brain of one man be connected ? In order to make the connection very intimate,
we collect everything which requires to be psychically connected in a single point,

although the connection is not explained by this procedure. Thus the psychological
monadic theory is created on the basis of a motive and of an illusion similar to that
on which the physical rests.
Let us assume for a moment
the proposition in the text; viz., that the atoms
are endowed with
feeling. By the space coordinates x, y, ,x', y', z'... of the
atoms are determined in the atoms internal conditions a, ?, y, a', ?', y'. . ., and vice
versa. For we feel by our senses our physical environment, and our physical in
vasions of our environment are conditioned by our sensations. The idea is then at
hand, a ? y. . . alone being directly given, to set up by the elimination of x, y, . . .
a ? y, a' ?' y'. . . . This latter point of view would be
equations directly between
very near to my present one, aside from the fact that the latter wholly rejects meta
physical considerations.
 FACTS AND MENTAL SYMBOLS. 20I

Valuable therefore as the conceptions may be which we men

tally (theoretically) supply in our pursuit of facts, briniging to bear,

as they do, older, richer, more general, and more familar experiences
on facts that stand alone, thus affording us a broader field of view,

nevertheless, the same may, as classical and

conceptions examples
our own demonstrate, lead us For a in
experience astray. theory,

deed, always puts in the place of a fact something different, something

more simple, which is qualified to represent it in some certain as

pect, but for the very reason that it is different does not represent it
in other aspects. When in the place of lightHuygens mentally put
the familiar phenomenon of sound, light itself appeared to him as a

thing that he knew, but with respect to polarisation, which sound

waves lack, as a thing with which he was doubly unacquainted. Our
theories are abstractions, which, while they place in relief thatwhich
is important for certain fixed cases, neglect almost necessarily, or
even disguise, what is important for other cases. The law of re
fraction looks upon rays of light as homogeneous straight lines, and
that is sufficient for the comprehension of the geometrical aspect of
the matter. But the propositions that relate to refraction will never
lead us to the fact that the rays of light are periodical, that they in
terfere. Just the contrary, the favorite and familiar conception of
a ray as a smooth straight line will rather render this discovery diffi
cult.

Only in rare cases will the resemblance between a fact and its
theoretical extend than we ourselves
conception further postulate.
Then the theoretical conception may lead to the discovery of new
facts, of which conical refraction, circular polarisation, and Hertz's

electric waves furnish examples that stand in opposition to those

given above. But as a general rule we have every reason to distin

guish sharply between our theoretical conceptions of phenomena
and that which we observe. The former must be regarded merely
as auxiliary instruments that have been created for a definite pur

pose and which possess permanent value only with respect to that
purpose. No one will seriously imagine for a moment that a real
circle with angles and sines actually performs functions in the re
fraction of light. Every one, on the contrary, regards the formula
202 THE MONIST.

= as a kind of geometrical model that imitates inform

sin^/sin/?
the refraction of light and takes itsplace in our mind. In this sense,
I take it, all the theoretical conceptions of physics?caloric, elec

light-waves, molecules, atoms, and energy?must be regarded

tricity,
as mere helps or expedients to facilitate our viewing things. Even
within the domain of physics itself the greatest care must be exer
cised in transferring theories from one department to another, and
above all more instruction is not to be expected from a theory than
from the facts themselves.

Butinstances were not lacking that demonstrated to me, how

much greater the confusion was which was produced by the direct
transference of theories, methods, and inquiries that were legitimate
in physics, into the field of psychology.
Allow me to illustrate this by a few examples.
A physicist observes an image on the retina of an excised eye,
notices that it is turned upside down with respect to the objects

imaged, and puts to himself very naturally the question, How

does a luminous point situated at the top come to be reflected on the
retina at the bottom ? He answers this question by the aid of diop
trical studies. If, now, this question, which is perfectly legitimate
in the province of physics, be transferred to the domain of psychol

ogy, only obscurity will be produced. The question why we see

the inverted retina-image upright, has no meaning as a psychological
problem. The light-sensations of the separate spots of the retina
are connected with sensations of locality from the very beginning,
and we name the places that correspond to the parts down, up.
Such a question cannot present itself to the perceiving subject.
It is the same with the well-known theory of projection. The

problem of the physicist is, to seek the luminous object-point of a

point imaged on the retina of the eye in the backward prolonged

ray passing through the point of intersection of the eye. For the
as the light-sensations
perceiving subject this problem does not exist,
of the retinal spots are connected from the beginning with determi
nate space-sensations. The entire theory of the psychological

origin of the "external" world by the projection of sensations out

wards is founded in my opinion on a mistaken transference of a
 FACTS AND MENTAL SYMBOLS. 203

physically formulated inquiry into the province of psychology. Our

sensations of sight and touch are bound up with, are connected
with, various different sensations of space, that is to say these sen
sations have an existence by the side of one another or outside of one
another, exist in other words in a spatial field, in which our body
fills but a part. That table is thus outside ofmy body.
self-evidently
A projection-problem does not present itself, is neither consciously
nor solved.
unconsciously
A physicist (Mariotte) makes the discovery that a certain spot
on the retina is blind. He is accustomed to associating with every

spatial point an imaged point, and with every imaged point a sen
sation. Hence
the question arises, What do we see at the points
that correspond to the blind spots, and how is the gap in the image
filled out? If the unfounded influence of the physicist's method of

procedure on the discussion of psychological questions be excluded,

itwill be found that no problem exists at all here. We see nothing
at the blind spots, the gap in the image is not filled out. The gap,
moreover, is not felt, for the reason that a defect of light-sensation
at a blind from the beginning can no more be perceived as a
s?ot
gap in the image than the blindness say of the skin of the back can
be so
perceived.
I have chosen intentionally simple and obvious examples, such
as render it clear what unnecessary confusion is caused the care
by
less transference of a conception or mode of thought which is valid
and serviceable in one domain, into another.

In the work of a celebrated German

ethnographer I read re

cently the following sentence: "This tribe of people deeply de

graded itself by the practise of cannibalism." By its side lay the

book of an English inquirer who deals with the same subject. The
latter simply puts the question why certain South-Sea islanders eat
human beings, finds out in the course of his inquiries that our own
ancestors also were once cannibals, and comes to understand the

position the Hindus take in the matter?a point of view that oc

curred once to my five-year-old boy who while eating a piece of meat
stopped suddenly shocked and cried out, "We are cannibals to the
" "
animals ! "Thou shalt not eat human beings is a very beautiful
 THE MONIST.

maxim ; but in the mouth of the ethnographer it sullies the calm

and noble lustre of unprepossession by which weso gladly discover
the true inquirer. But a step further and we will say, " Man must
not be descended from monkeys/' "The earth shall not rotate,"
<(Matter
ought not everywhere to fill space," "Energy must be con
stant," and so on. I believe that our procedure differs from that

just characterised only in degree and not in kind, when we transfer

views reached in the province of physics with the dictum of sover

eign validity into the domain of psychology, where they should be

tested anew with respect to their serviceability. In such cases we
are subject to dogma, if not to that which is forced upon us by a

power from without like our scholastic forefathers, yet to that which
we have made ourselves. And what result of research is there that
could not become a dogma by long habit of use, since the very skill
which we have acquired in familiar intellectual situations, deprives
us of the freshness and unprepossession which are so requisite in a
new situation.

Now that I have set forth in general outlines the position I take,
I may be able perhaps to establish my opposition to the dualism of

feeling and motion. This dualism is to my mind an artificial and an

unnecessary one. The way it has arisen is to that in
analogous
which the imaginary solutions of certain mathematical problems
have arisen?by the improper formulation of the questions involved.
In the investigation of purely physical processes we generally

employ notions so abstract that as a rule we only think cursorily or

not at all of the sensations that lie at and constitute their foundation.
Por example, when I establish the fact that an electric current of

Amp?re develops 10^ cubic centimetres oxyhydrogen gas at oQ C.

and 760 mm mercury pressure in a minute, I am easily disposed to
attribute to the objects defined a reality wholly independent of my
sensations. But I am obliged in order to arrive at what I have de
termined to conduct the current through a circular wire having a
definite measured radius, so that the current, the intensity of terres
trial magnetism being given, shall turn the magnetic needle at its
centre a certain angular distance out of the meridian. The inten

sity of terrestrial magnetism must have been disclosed by a definite

 FACTS AND MENTAL SYMBOLS. 205

observed period of vibration of a magnetic needle of measured di

mensions, known weight, and so forth. The determination of the
oxyhydrogen gas is no less intricate. The whole statement, so sim

ple in its appearance, is based upon an almost unending series of

simple sensory observations (sensations), particularly so when the

observations are added that guarantee the adjustment of the appa
ratus, which may have been performed in part long before the actual
experiment. Now itmay easily happen to the physicist who does
not study the psychology of his operations, that he does not (to re
verse a well-known saying) see the trees for the woods, and that he
slurs over the sensory elements at the foundation of his work. Now
I maintain, that every physical notion is nothing more than a definite
connection of the sensory elements which C . .
I denote
by A
and that every physical fact rests therefore on such a connection.
These elements?elements in the sense that no further resolution has

for the present been effected of them?are themost ultimate building

stones of the physical world that we have as yet been able to seize.

Physiological research also may have a purely physical charac

ter. I can follow the course of a physical process as it propagates
itself through a sensitive nerve to the spinal column and brain of an
animal and returns by various paths to the muscles of the animal,
whose contraction produces further events in the environment of the
animal. I need not think, in so doing, of any feeling on the part of
the animal ; what I investigate is a purely physical object. Very
much is lacking, it is true, to our complete comprehension of the de
tails of this process, and the assurance that it is all motion can
neither console me nor deceive me with to my
respect ignorance.

Long before there was any scientific physiology people per

ceived that the behavior of an animal confronted by physical influ
ences is much better viewed, that is understood, by attributing to
the animal sensations like our own. To that which I see, to my sen

sations, I have to supply mentally the sensations of the animal, which

are not to be found in the province of my own sensation. This con:

trariety appears still more abrupt to the scientific inquirer who is

investigating a nervous process by the aid of colorless abstract no
tions, and is required for example to add mentally to that process
2 6 THE MONIST.

the sensation green. This last can appear as

actually something

entirely novel, and we can ask ourselves how it is that this miracu
lous thing is produced from chemical processes, electrical currents,

and the like.*

Psychological analysis has taught us that this surprise is un

justified, since the physicist deals with sensations in everything on
which he employs himself. This analysis is also able to render it
clear to us that the mental addition by analogy of sensations and
complexes of sensations which at the time being are not present in
the field of sense or cannot even come into it, is also daily practised

by the physicist, as when for example he imagines the moon an

inert heavy mass although he cannot touch the moon but only see it.
The totally strange character of the intellectual situation above
described is therefore an illusion.
The illusion disappears when I make observations (psycholog

ically) on my own person which are limited to the sensory sphere.

Before me lies the leaf of a plant. The green (A) of the leaf is
united with a certain optical sensation of space (B) and sensation of
touch (C), with the visibility of the sun or the lamp ?D). If the

yellow (E) of a sodium flame takes the place of the sun, the green
(A) will pass into brown (E). If the chlorophyl granules be re
moved,?an like the one ele
operation representable preceding by

ments,?the green (A) will pass intowhite (G). All these observations
are physical observations. But the green (?) is also united with a
certain process on my retina. There is to prevent me in
nothing

* The : To what kind of nervous processes

following is a legitimate question is
the sensation green to be mentally added. Such questions can be solved only by

special inquiry, and not by a reference in a general way to motion and electric cur
rents. How disadvantageous our remaining satisfied with such general conceptions
is, can be seen from the fact that inquirers have been repeatedly on the brink of
abandoning the specific energies, one of the greatest acquisitions we have made,

simply because they were unable to discover any difference in the currents of dif
ferent sensory nerves. I was impelled as early as 1863 in my lectures on psycho

physics to call attention to the fact that the most diverse kinds of nervous
processes
can conceal themselves in a current. Current is an abstraction
and places in relief
but one feature of the process?the passage of energy though a transverse section.
A current in diluted sulphuric acid is something entirely different from a current in

copper. We must therefore also expect that a current in the acoustic nerve is some
thing entirely different from a current in the optic nerve.
 FACTS AND MENTAL SYMBOLS. 207

principle from physically investigating this process on my own eye

in exactly the same manner as in the cases set forth, and
previously
from it to its elements X Y Z. . . . If this were not
reducing possible
in the case of my own eye, it might be accomplished with that of

another, and the gap filled out by analogy exactly as in physical in

Now in its B C D . . ., A is a
vestigations. dependence upon

element, in its on X Y Z . . . it is a sensation.

physical dependence
The green (A) however is not altered at all in itself, whether we di
rect our. attention to the one or to the other form of dependence.
I see, therefore, no opposition of physical and psychical, no duality, but

simply identity. In the sensory sphere of my consciousness every

thing is at once physical and psychical.

The obscurity of this intellectual situation has arisen according
to my conviction from the transference of a prepos
solely physical
session into the domain of psychology. The physicist says: I find

everywhere bodies and the motions of bodies no sensations ;

only,
sensation therefore must be something entirely diferent from the

physical objects I deal with. The psychologist accepts the second

portion of this declaration. To him, it is true, sensation is given,

but there corresponds to it a mysterious physical something which

to physical must be from sensa

conformably prepossession different
tion. But what is it that is the really mysterious thing ? Is it the
Physis or the Psyche ? or is it perhaps both? It would almost ap
pear so, as it is now the one and now the other that is intangible.

Or does the whole involved rest on a fallacious circle ?

reasoning
I believe that the latter is the case. For me the elements des

. . are
ignated by A B C. immediately and indubitably given, and

for me they can never afterwards be volatilised away by any con

siderations which are after all based in every case on their existence.*

* It is the transitoriness of sense-perceptions that so easily leads us to regard

them as mere appearances as contrasted with permanent hodies. I have repeatedly
pointed out that unconditioned permanent states do not exist in nature, that per
manences of connection only exist. A body is for me the same complex of sight
and-touch-sensations every time that it is placed in the same circumstances of illu
mination, position in space, temperature, and so forth. The supposed constancy of
the body is the constancy of the union of A, B, C. . . or the constancy of the
egua
11nn f(A B,R C.\
2 8 the monist.

To
the department of special research having for its subject the

sensory, physical, and psychical province which is not made super

fluous by this general orientation and which cannot be forestalled,
the relations of A C . ?. . remain to be ascertained. This
only

may be expressed symbolically by saying that it is the purpose and

end of special research to find equations of the formf{A, B, C,
. . = o.
.)
I hope with this to have designated the point inwhich I am
in opposition to Dr. Carus, with whom I agree so much in other re

spects. I am obliged, notwithstanding the latter fact, to regard

this point as essential, inasmuch as my whole mode of thinking and
direction of inquiry have been changed by the view it involves, and
because, moreover, I do not believe that the difference in question
can be dissipated by any verbal explanations however exact.
This whole train of reasoning has forme simply the significance
of negative orientation for the avoidance of pseudo-problems. I

restrict moreover here, to the question of sense

myself, intentionally

perceptions, for the reason

that at the start exact special research
will find here alone a safe basis of operations.

Ernst Mach.