I perceive 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 opinion exists between us on an important question of
special character. As I was not successful in rendering my thought clear
on this point, I shall endeavor on the present occasion to explain _what_
it was 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 supposition
that our difference of opinion is merely apparent and can be adjusted
by a precise agreement as to the terms employed is a very natural one
in philosophical discussions. 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 in my youth physical _and_
philosophical studies, particularly psychology, with equal ardor. There
was hardly the question at that time of an experimental psychology, of
a relation of psychological to physiological research. No more so did
physics at that day think of a psychological analysis of the notions it
was constantly employing. How the notions of “body,” “matter,” “atom,”
etc., were come by, was not investigated. 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
_unconciliated_ the one by the side of the other, each having its own
particular concepts, methods, and theories. No one questioned, indeed,
that the two departments were connected in some way. _The way_, however,
appeared an insoluble riddle; as it yet appears to Dubois-Reymond.
Now although this condition of things was not such as to satisfy my mind,
it was nevertheless natural that as a student I should seek to acquire
tentatively the prevailing views of both provinces and put them into
consistent connection with one another.
I thus formed provisorily the view that Nature has two _sides_—a physical
and a psychological side. If psychical life is to be harmonised 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 processes, 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 psychologists (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 knowledge
assumes in these monadic theories as contradistinguished from the facts
that deserve knowledge, and how poorly such theories satisfy in the long
run a vigorous mind. As a fact, employment with this cumbrous artifice
was in my case the means that effected very soon the appearance of my
better conviction, already latently present.[34]
In the further progress of my physical work I soon discovered that it was
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 phenomena of conduction and 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 quantity of heat-substance _prevented_ on the other hand Black’s
successors from using their eyes. They no longer mark the fact which
every savage knows, that heat is _produced_ 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 longitudinal 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 way of_ the discovery of the specific inductive
capacity, which was reserved for the eye of Faraday undimmed by any
traditional theories.
Valuable therefore as the conceptions may be which we mentally
(theoretically) supply in our pursuit of facts, bringing to bear, as
they do, older, richer, more general, and more familiar experiences
on facts that stand alone, thus affording us a broader field of view,
nevertheless, the same conceptions may, as classical examples and our
own experience demonstrate, lead us astray. For a theory, indeed, always
puts in the place of a fact something _different_, something more
simple, which is qualified to represent it in some _certain_ aspect,
but for the very reason that it is different does _not_ represent it
in other aspects. When in the place of _light_ Huygens 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 that which is important
for _certain fixed_ cases, neglect almost necessarily, or even disguise,
what is important for other cases. The law of refraction 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 interfere. Just the
contrary, the favorite and familiar conception of a ray as a smooth
straight line will rather render this discovery difficult.
Only in rare cases will the resemblance between a fact and its
theoretical conception extend _further_ than we ourselves 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 distinguish 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_ purpose 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 refraction of light. Every one, on the contrary, regards the formula
sinα/sinβ = _n_ as a kind of geometrical model that _imitates in form_
the refraction of light and _takes its place_ in our mind. In this
sense, I take it, all the theoretical conceptions of physics—caloric,
electricity, light-waves, molecules, atoms, and energy—must be regarded
as mere helps or expedients to facilitate our viewing things. Even
within the domain of physics itself the greatest care must be exercised
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.
But instances 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 dioptrical studies. If, now, this
question, which is perfectly legitimate in the province of physics, be
transferred to the domain of psychology, 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 perceiving subject this
_problem_ does not exist, as the light-sensations of the retinal spots
are connected from the beginning with determinate space-sensations. The
entire theory of the psychological origin of the “external” world by the
projection of sensations outwards is founded in my opinion on a mistaken
transference of a _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 sensations 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 self-evidently
_outside of_ my body. A projection-problem does not present itself, is
neither consciously nor unconsciously solved.
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 sensation. 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, it will 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 spot blind from the beginning can
no more be perceived as a 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 by the careless
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 recently the
following sentence: “This tribe of people deeply degraded 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 occurred 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 maxim; but in the mouth of the ethnographer it sullies the
calm and noble lustre of unprepossession by which we so 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 constant,” 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 sovereign 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 analogous to that in 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.
For example, when I establish the fact that an electric current of 1
Ampère develops 10½ cubic centimetres oxyhydrogen gas at 0° 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 determined to conduct
the current through a circular wire having a definite measured radius,
so that the current, the intensity of terrestrial magnetism being
given, shall turn the magnetic needle at its centre a certain angular
distance out of the meridian. The intensity of terrestrial magnetism
must have been disclosed by a definite observed period of vibration
of a magnetic needle of measured dimensions, known weight, and so
forth. The determination of the oxyhydrogen gas is no less intricate.
The whole statement, so simple 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 apparatus, which may have been performed in part long
before the actual experiment. Now it may easily happen to the physicist
who does not study the psychology of his operations, that he does not
(to reverse 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 I denote by _A_ _B_ _C_ ...,
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 the most ultimate building stones of
the physical world that we have as yet been able to seize.
Physiological research also may have a purely physical character. 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 details of this process, and the assurance that it
is all motion can neither console me nor deceive me with respect to my
ignorance.
Long before there was any scientific physiology people perceived that the
behavior of an animal confronted by physical influences is much better
viewed, that is understood, by attributing to the animal _sensations_
like our own. To that which I see, to _my_ sensations, I have to _supply
mentally_ the sensations of the _animal_, which are not to be found in
the province of my own sensation. This contrariety appears still more
abrupt to the scientific inquirer who is investigating a nervous process
by the aid of colorless abstract notions, and is required for example
to add mentally to that process the sensation green. This last can
actually appear as something entirely novel, and we can ask ourselves how
it is that this miraculous thing is produced from chemical processes,
electrical currents, and the like.[35]
Psychological analysis has taught us that this surprise is unjustified,
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 (psychologically) 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
(_F_). If the chlorophyl granules be removed,—an operation representable
like the preceding one by elements,—the green (_A_) will pass into white
(_G_). All these observations are _physical_ observations. But the
green (_A_) is also united with a certain process on my retina. There
is nothing to prevent me in principle from physically investigating
this process on my own eye in exactly the same manner as in the cases
previously set forth, and from reducing it to its elements _X_ _Y_
_Z_.... If this were not 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 investigations. Now in its dependence upon _B_ _C_
_D_ ..., _A_ is a _physical element_, in its dependence on _X_ _Y_ _Z_
... it is a _sensation_. The green (_A_) however is not altered at all
_in itself_, whether we direct our attention to the one or to the other
form of dependence. _I see, therefore, no oppositions of physical and
psychical, no duality, but simply identity._ In the sensory sphere of my
consciousness everything is at once physical and psychical.
The obscurity of this intellectual situation has arisen according to
my conviction solely from the transference of a physical prepossession
into the domain of psychology. The physicist says: I find everywhere
bodies and the motions of bodies only, no sensations; sensation therefore
must be something _entirely different_ 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 conformably to physical prepossession
must be _different_ from sensation. 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 appear so, as it is now the one and now the
other that is intangible. Or does the whole reasoning involved rest on a
fallacious circle?
I believe that the latter is the case. For me the elements designated by
_A_ _B_ _C_ ... are immediately and indubitably given, and for me they
can never afterwards be volatilised away by any considerations which are
after all based in every case on their existence.[36]
To the department of special research having for its subject the sensory,
physical, and psychical province which is not made superfluous by this
general orientation and Which cannot be forestalled, the relations of
_A_ _B_ _C_ ... only remain to be ascertained. This may be expressed
symbolically by saying that it is the purpose and end of special research
to find equations of the form _f(A, B, C_, ...) = 0.
I hope with this to have designated the point in which I am in opposition
to Dr. Carus, with whom I agree so much in other respects. 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 for me simply the significance
of negative orientation for the avoidance of pseudo-problems. I
restrict myself, moreover intentionally here, to the question of
sense-perceptions, for the reason that at the start exact special
research will find here alone a safe basis of operations.