CONSCIOUSNESS
Consciousness as a Natural Phenomenon--Its Definition--Difficulties
of the Problem--Its Relation to the Life of the Soul--Our
Human Consciousness--Various Theories: I. Anthropistic
Theory (Descartes); II. Neurological Theory (Darwin);
III. Animal Theory (Schopenhauer); IV. Biological Theory
(Fechner); V. Cellular Theory (Fritz Schultze); VI. Atomistic
Theory--Monistic and Dualistic Theories--Transcendental
Character of Consciousness--The Ignorabimus Verdict of Du
Bois-Reymond--Physiology of Consciousness--Discovery of the
Organs of Thought by Flechsig--Pathology--Double and Intermittent
Consciousness--Ontogeny of Consciousness: Modifications at
Different Ages--Phylogeny of Consciousness--Formation of Concepts
No phenomenon of the life of the soul is so wonderful and so variously
interpreted as consciousness. The most contradictory views are current
to-day, as they were two thousand years ago, not only with regard to
the nature of this psychic function and its relation to the body,
but even as to its diffusion in the organic world and its origin and
development. It is more responsible than any other psychic faculty for
the erroneous idea of an "immaterial soul" and the belief in "personal
immortality"; many of the gravest errors that still dominate even
our modern civilization may be traced to it. Hence it is that I have
entitled consciousness "the central mystery of psychology"; it is
the strong citadel of all mystic and dualistic errors, before whose
ramparts the best-equipped efforts of reason threaten to miscarry. This
fact would suffice of itself to induce us to make a special critical
study of consciousness from our monistic point of view. We shall see
that consciousness is simply a natural phenomenon like any other
psychic quality, and that it is subject to the law of substance like
all other natural phenomena.
Even as to the elementary idea of consciousness, its contents and
extension, the views of the most distinguished philosophers and
scientists are widely divergent. Perhaps the meaning of consciousness
is best conceived as an _internal perception_, and compared with the
action of _a mirror_. As its two chief departments we distinguish
objective and subjective consciousness--consciousness of the world,
the non-ego, and of the ego. By far the greater part of our conscious
activity, as Schopenhauer justly remarked, belongs to the consciousness
of the outer world, or the non-ego: this _world-consciousness_
embraces all possible phenomena of the outer world which are in any
sense accessible to our minds. Much more contracted is the sphere
of _self-consciousness_, the internal mirror of all our own psychic
activity, all our presentations, sensations, and volitions.
Many distinguished thinkers, especially on the physiological side
(Wundt and Ziehen, for instance) take the ideas of consciousness and
psychic function to be identical--"all psychic action is conscious";
the province of psychic life, they say, is coextensive with that
of consciousness. In our opinion, such a definition gives an undue
extension to the meaning of consciousness, and occasions many
errors and misunderstandings. We share, rather, the view of other
philosophers (Romanes, Fritz Schultze, and Paulsen), that even our
unconscious presentations, sensations, and volitions pertain to our
psychic life; indeed, the province of these unconscious psychic actions
(reflex action, and so forth) is far more extensive than that of
consciousness. Moreover, the two provinces are intimately connected,
and are separated by no sharp line of demarcation. An unconscious
presentation may become conscious at any moment; let our attention be
withdrawn from it by some other object, and forthwith it disappears
from consciousness once more.
The only source of our knowledge of consciousness is that faculty
itself; that is the chief cause of the extraordinary difficulty of
subjecting it to scientific research. Subject and object are one and
the same in it: the perceptive subject mirrors itself in its own
inner nature, which is to be the object of our inquiry. Thus we can
never have a complete objective certainty of the consciousness of
others; we can only proceed by a comparison of their psychic condition
with our own. As long as this comparison is restricted to _normal_
people we are justified in drawing certain conclusions as to their
consciousness, the validity of which is unchallenged. But when we pass
on to consider _abnormal_ individuals (the genius, the eccentric, the
stupid, or the insane) our conclusions from analogy are either unsafe
or entirely erroneous. The same must be said with even greater truth
when we attempt to compare human consciousness with that of the animals
(even the higher, but especially the lower). In that case such grave
difficulties arise that the views of physiologists and philosophers
diverge as widely as the poles on the subject. We shall briefly
enumerate the most important of these views.
I. _The anthropistic theory of consciousness._--It is peculiar to man.
To Descartes we must trace the widespread notion that consciousness
and thought are man's exclusive prerogative, and that he alone is
blessed with an "immortal soul." This famous French philosopher and
mathematician (educated in a Jesuit College) established a rigid
partition between the psychic activity of man and that of the brute.
In his opinion the human soul, a thinking, immaterial being, is
completely separated from the body, which is extended and material.
Yet it is united to the body at a certain point in the brain (the
_glandula pinealis_) for the purpose of receiving impressions from the
outer world and effecting muscular movements. The animals, not being
endowed with thought, have no soul: they are mere automata, or cleverly
constructed machines, whose sensations, presentations, and volitions
are purely mechanical, and take place according to the ordinary laws
of physics. Hence Descartes was a _dualist_ in human psychology, and
a _monist_ in the psychology of the brute. This open contradiction in
so clear and acute a thinker is very striking; in explaining it, it
is not unnatural to suppose that he concealed his real opinion, and
left the discovery of it to independent scholars. As a pupil of the
Jesuits, Descartes had been taught to deny the truth in the face of his
better insight; and perhaps he dreaded the power and the fires of the
Church. Besides, his sceptical principle, that every sincere effort to
attain the truth must start with a doubt of the traditional dogma had
already drawn upon him fanatical accusations of scepticism and atheism.
The great influence which Descartes had on subsequent philosophy was
very remarkable, and entirely in harmony with his "book-keeping by
double entry." The _materialists_ of the seventeenth and eighteenth
centuries appealed to the Cartesian theory of the animal soul and its
purely mechanical activity in support of their monistic psychology. The
_spiritualists_, on the other hand, asserted that their dogma of the
immortality of the soul and its independence of the body was firmly
established by Descartes' theory of the human soul. This view is still
prevalent in the camp of the theologians and dualistic metaphysicians.
The scientific conception of nature, however, which has been built up
in the nineteenth century, has, with the aid of empirical progress, in
physiological and comparative psychology, completely falsified it.
II. _Neurological theory of consciousness._--It is present only
in man and those higher animals which have a centralized nervous
system and organs of sense. The conviction that a large number of
animals--at least the higher mammals--are not less endowed than man
with a thinking soul and consciousness prevails in modern zoology,
exact physiology, and the monistic psychology. The immense progress we
have made in the various branches of biology has contributed to bring
about a recognition of this important truth. We confine ourselves for
the present to the higher vertebrates, and especially the mammals.
That these most intelligent specimens of these highly developed
vertebrates--apes and dogs, in particular--have a strong resemblance to
man in their whole psychic life has been recognized and speculated on
for thousands of years. Their faculty of presentation and sensation,
of feeling and desire, is so like that of man that we need adduce no
proof of our thesis. But even the higher associational activity of
the brain, the formation of judgments and their connection into chains
of reasoning, thought, and consciousness in the narrower sense, are
developed in them after the same fashion as in man: they differ only in
degree, not in kind. Moreover, we learn from comparative anatomy and
histology that the intricate structure of the brain (both in general
and in detail) is substantially the same in the mammals as it is in
man. The same lesson is enforced by comparative ontogeny with regard
to the origin of these psychic organs. Comparative physiology teaches
us that the various states of consciousness are just the same in these
highest placentals as in man; and we learn by experiment that there
is the same reaction to external stimuli. The higher animals can be
narcotized by alcohol, chloroform, ether, etc., and may be hypnotized
by the usual methods, just as in the case of man.
It is, however, impossible to determine mathematically at what stage
of animal life consciousness is to be first recognized as such. Some
zoologists draw the line very high in the scale, others very low.
Darwin, who most accurately distinguishes the various stages of
consciousness, intelligence, and emotion in the higher animals, and
explains them by progressive evolution, points out how difficult,
or even impossible, it is to determine the first beginning of this
supreme psychic faculty in the lower animals. Personally, out of the
many contradictory theories, I take that to be most probable which
holds _the centralization of the nervous system_ to be a condition of
consciousness; and that is wanting in the lower classes of animals. The
presence of a central nervous organ, of highly developed sense-organs,
and an elaborate association of groups of presentations, seem to me to
be required before the unity of consciousness is possible.
III. _Animal theory of consciousness._--All animals, and they alone,
have consciousness. This theory would draw a sharp distinction between
the psychic life of the animal and of the plant. Such a distinction
was urged by many of the older writers, and was clearly formulated
by Linné in his celebrated _Systema Naturae_; the two great kingdoms
of the organic world are, in his opinion, divided by the fact that
animals have sensation and consciousness, and the plants are devoid
of them. Later on Schopenhauer laid stress on the same distinction:
"Consciousness is only known to us as a feature of animal nature.
Even though it extend upwards through the whole animal kingdom, even
to man and his reason, the unconsciousness of the plant, from which
it started, remains as the basic feature. In the lowest animals we
have but the dawn of it." The inaccuracy of this view was obvious by
about the middle of the present century, when a deeper study was made
of the psychic activity of the lower animal forms, especially the
coelenterates (sponges and cnidaria): they are undoubtedly animals,
yet there is no more trace of a definite consciousness in them than in
most of the plants. The distinction between the two kingdoms was still
further obliterated when more careful research was made into their
unicellular forms. There is no psychological difference between the
plasmophagous protozoa and the plasmodomous protophyta, even in respect
of their consciousness.
IV. _Biological theory of consciousness._--It is found in all
organisms, animal or vegetal, but not in lifeless bodies (such as
crystals). This opinion is usually associated with the idea that all
organisms (as distinguished from inorganic substances) have souls:
the three ideas--life, soul, and consciousness--are then taken to be
coextensive. Another modification of this view holds that, though
these fundamental phenomena of organic life are inseparably connected,
yet consciousness is only a part of the activity of the soul, and of
the vital activity. Fechner, in particular, has endeavored to prove
that the plant has a "soul," in the same sense as an animal is said
to have one; and many credit the vegetal soul with a consciousness
similar to that of the animal soul. In truth, the remarkable stimulated
movements of the leaves of the sensitive plants (the mimosa, drosera,
and dionæa), the automatic movements of other plants (the clover
and wood-sorrel, and especially the hedysarum), the movements of
the "sleeping plants" (particularly the _papilionacea_), etc., are
strikingly similar to the movements of the lower animal forms: whoever
ascribes consciousness to the latter cannot refuse it to such vegetal
forms.
V. _Cellular theory of consciousness._--It is a vital property of every
cell. The application of the cellular theory to every branch of biology
involved its extension to psychology. Just as we take the living cell
to be the "elementary organism" in anatomy and physiology, and derive
the whole system of the multicellular animal or plant from it, so, with
equal right, we may consider the "cell-soul" to be the psychological
unit, and the complex psychic activity of the higher organism to be
the result of the combination of the psychic activity of the cells
which compose it. I gave the outlines of this _cellular psychology_
in my _General Morphology_ in 1866, and entered more fully into the
subject in my paper on "Cell-Souls and Soul-Cells." I was led to a
deeper study of this "elementary psychology" by my protracted research
into the unicellular forms of life. Many of these tiny (generally
microscopic) protists show similar expressions of sensation and will,
and similar instincts and movements, to those of higher animals; that
is especially true of the very sensitive and lively infusoria. In the
relation of these sensitive cell-organisms to their environment, and in
many other of their vital expressions (for instance, in the wonderful
architecture of the rhizopods, the thalamophoræ, and the infusoria),
we seemed to have clear indications of conscious psychic action. If,
then, we accept the biological theory of consciousness (No. IV.), and
credit every psychic function with a share of that faculty, we shall be
compelled to ascribe it to each independent protist cell. In that case
its material basis would be either the entire protoplasm of the cell,
or its nucleus, or a portion of it. In the "psychade theory" of Fritz
Schultze the elementary consciousness of the _psychade_ would have
the same relation to the individual cells as personal consciousness
has to the multicellular organism of the personality in the higher
animals and man. It is impossible definitively to disprove this theory,
which I held at one time. Still, I now feel compelled to agree with
Max Verworn, in his belief that none of the protists have a developed
self-consciousness, but that their sensations and movements are of an
unconscious character.
VI. _Atomistic theory of consciousness._--It is an elementary property
of all atoms. This atomistic hypothesis goes furthest of all the
different views as to the extension of consciousness. It certainly
escapes the difficulty which so many philosophers and biologists
experience in solving the problem of the first origin of consciousness.
It is a phenomenon of so peculiar a character that a derivation of
it from other psychic functions seems extremely hazardous. It seemed,
therefore, the easiest way out of the difficulty to conceive it as an
inherent property of all matter, like gravitation or chemical affinity.
On that hypothesis there would be as many forms of this original
consciousness as there are chemical elements; each atom of hydrogen
would have its hydrogenic consciousness, each atom of carbon its
carbonic consciousness, and so forth. There are philosophers, even, who
ascribe consciousness to the four elements of Empedocles, the union of
which, by "love and hate," produces the totality of things.
Personally, I have never subscribed to this hypothesis of atomic
consciousness. I emphasize the point because Emil du Bois-Reymond
has attributed it to me. In the controversy I had with him (1880) he
violently attacked my "pernicious and false philosophy," and contended
that I had, in my paper on "The Perigenesis of the Plastidule," "laid
it down as a metaphysical axiom that every atom has its individual
consciousness." On the contrary, I explicitly stated that I conceive
the elementary psychic qualities of sensation and will, which may
be attributed to atoms, to be _unconscious_--just as unconscious as
the elementary memory which I, in company with that distinguished
physiologist, Ewald Hering, consider to be "a common function of
all organized matter"--or, more correctly, "living substance." Du
Bois-Reymond curiously confuses "soul" and "consciousness"; whether
from oversight or not I cannot say. Since he considers consciousness
to be a transcendental phenomenon (as we shall see presently), while
denying that character to other psychic functions--the action of the
senses, for example--I must infer that he recognizes the difference
of the two ideas. Other parts of his eloquent speeches contain quite
the opposite view, for the famous orator not infrequently contradicts
himself on important questions of principle. However, I repeat that, in
my opinion, consciousness is only _part_ of the psychic phenomena which
we find in man and the higher animals; the great majority of them are
unconscious.
However divergent are the different views as to the nature and
origin of consciousness, they may, nevertheless, on a clear and
logical examination, all be reduced to two fundamental theories--the
transcendental (or dualistic) and the physiological (or monistic).
I have myself always held the latter view, in the light of my
evolutionary principles, and it is now shared by a great number of
distinguished scientists, though it is by no means generally accepted.
The transcendental theory is the older and much more common; it
has recently come once more into prominence, principally through
Du Bois-Reymond, and it has acquired a great importance in modern
discussions of cosmic problems through his famous "Ignorabimus speech."
On account of the extreme importance of this fundamental question we
must touch briefly on its main features.
In the celebrated discourse on "The Limits of Natural Science,"
which E. du Bois-Reymond gave on August 14, 1872, at the Scientific
Congress at Leipzig, he spoke of two "absolute limits" to our possible
knowledge of nature which the human mind will never transcend in its
most advanced science--_never_, as the oft-quoted termination of the
address, "Ignorabimus," emphatically pronounces. The first absolutely
insoluble "world-enigma" is the "connection of matter and force," and
the distinctive character of these fundamental natural phenomena; we
shall go more fully into this "problem of substance" in the twelfth
chapter. The second insuperable difficulty of philosophy is given as
the problem of consciousness--the question how our mental activity
is to be explained by material conditions, especially movements, how
"substance [the substance which underlies matter and force] comes,
under certain conditions, to feel, to desire, and to think."
For brevity, and in order to give a characteristic name to the Leipzig
discourse, I have called it the "Ignorabimus speech"; this is the
more permissible, as E. du Bois-Reymond himself, with a just pride,
eight years afterwards, speaking of the extraordinary consequences
of his discourse, said: "Criticism sounded every possible note, from
friendly praise to the severest censure, and the word 'Ignorabimus,'
which was the culmination of my inquiry, was at once transformed into a
kind of scientific shibboleth." It is quite true that loud praise and
approbation resounded in the halls of the dualistic and spiritualistic
philosophy, and especially in the camp of the "Church militant"; even
the spiritists and the host of believers, who thought the immortality
of their precious souls was saved by the "Ignorabimus," joined in the
chorus. The "severest censure" came at first only from a few scientists
and philosophers--from the few who had sufficient scientific knowledge
and moral courage to oppose the dogmatism of the all-powerful secretary
and dictator of the Berlin Academy of Science.
Towards the end, however, the author of the "Ignorabimus speech" briefly
alluded to the question whether these two great "world-enigmas," the
general problem of substance and the special problem of consciousness,
are not two aspects of one and the same problem. "This idea," he said,
"is certainly the simplest, and preferable to the one which makes the
world doubly incomprehensible. Such, however, is the nature of things
that even here we can obtain no clear knowledge, and it is useless to
speak further of the question." The latter sentiment I have always
stoutly contested, and have endeavored to prove that the two great
questions are not two distinct problems. "The neurological problem
of consciousness is but a particular aspect of the all-pervading
cosmological problem of substance."
The peculiar phenomenon of consciousness is not, as Du Bois-Reymond
and the dualistic school would have us believe, a completely
"transcendental" problem; it is, as I showed thirty-three years ago,
a _physiological_ problem, and, as such, must be reduced to the
phenomena of physics and chemistry. I subsequently gave it the more
definite title of a _neurological_ problem, as I share the view that
true consciousness (thought and reason) is only present in those higher
animals which have a centralized nervous system and organs of sense
of a certain degree of development. Those conditions are certainly
found in the higher vertebrates, especially in the placental mammals,
the class from which man has sprung. The consciousness of the highest
apes, dogs, elephants, etc., differs from that of man in degree only,
not in kind, and the graduated interval between the consciousness of
these "rational" placentals and that of the lowest races of men (the
Veddahs, etc.) is less than the corresponding interval between these
uncivilized races and the highest specimens of thoughtful humanity
(Spinoza, Goethe, Lamarck, Darwin, etc.). Consciousness is but a part
of the higher activity of the soul, and as such it is dependent on the
normal structure of the corresponding psychic organ, the brain.
Physiological observation and experiment determined twenty years ago
that the particular portion of the mammal-brain which we call the
_seat_ (preferably the _organ_) of consciousness is a part of the
cerebrum, an area in the late-developed gray bed, or cortex, which
is evolved out of the convex dorsal portion of the primary cerebral
vesicle, the "fore-brain." Now, the morphological proof of this
physiological thesis has been successfully given by the remarkable
progress of the microscopic anatomy of the brain, which we owe to the
perfect methods of research of modern science (Kölliker, Flechsig,
Golgi, Edinger, Weigert, and others).
The most important development is the discovery of the _organs of
thought_ by Paul Flechsig, of Leipzig; he proved that in the gray bed
of the brain are found the four seats of the central sense-organs,
or four "inner spheres of sensation"--the sphere of touch in the
vertical lobe, the sphere of smell in the frontal lobe, the sphere
of sight in the occipital lobe, and the sphere of hearing in the
temporal lobe. Between these four "sense-centres" lie the four great
"thought-centres," or centres of association, the _real organs of
mental life_; they are those highest instruments of psychic activity
that produce thought and consciousness. In front we have the frontal
brain or centre of association; behind, on top there is the vertical
brain, or parietal centre of association, and underneath the principal
brain, or "the great occipito-temporal centre of association" (the
most important of all); lower down, and internally, the insular brain
or the insula of Reil, the insular centre of association. These four
"thought-centres," distinguished from the intermediate "sense-centres"
by a peculiar and elaborate nerve-structure, are the true and sole
organs of thought and consciousness. Flechsig has recently pointed out
that, in the case of man, very specific structures are found in one
part of them; these structures are wanting in the other mammals, and
they, therefore, afford an explanation of the superiority of man's
mental powers.
The momentous announcement of modern physiology, that the cerebrum is
the organ of consciousness and mental action in man and the higher
mammals, is illustrated and confirmed by the pathological study of
its diseases. When parts of the cortex are destroyed by disease their
respective functions are affected, and thus we are enabled, to some
extent, to localize the activities of the brain; when certain parts
of the area are diseased, that portion of thought and consciousness
disappears which depends on those particular sections. Pathological
experiment yields the same result; the decay of some known area (for
instance, the centre of speech) extinguishes its function (speech).
In fact, there is proof enough in the most familiar phenomena of
consciousness of their complete dependence on chemical changes in
the substance of the brain. Many beverages (such as coffee and
tea) stimulate our powers of thought; others (such as wine and
beer) intensify feeling; musk and camphor reanimate the fainting
consciousness; ether and chloroform deaden it, and so forth. How
would that be possible if consciousness were an immaterial entity,
independent of these anatomical organs? And what becomes of the
consciousness of the "immortal soul" when it no longer has the use of
these organs?
These and other familiar facts prove that man's consciousness--and
that of the nearest mammals--is _changeable_, and that its activity
is always open to modification from inner (alimentation, circulation,
etc.) and outer causes (lesion of the brain, stimulation, etc.).
Very instructive, too, are the facts of double and intermittent
consciousness, which remind us of "alternate generations of
presentations." The same individual has an entirely different
consciousness on different days, with a change of circumstances; he
does not know to-day what he did yesterday: yesterday he could say, "I
am I"; to-day he must say, "I am another being." Such intermittence of
consciousness may last not only days, but months, and even years; the
change may even become permanent.
As everybody knows, the new-born infant has no consciousness. Preyer
has shown that it is only developed after the child has begun to
speak; for a long time it speaks of itself in the third person.
In the important moment when it first pronounces the word "I,"
when the feeling of self becomes clear, we have the beginning of
self-consciousness, and of the antithesis to the non-ego. The rapid
and solid progress in knowledge which the child makes in its first
ten years, under the care of parents and teachers, and the slower
progress of the second decade, until it reaches complete maturity of
mind, are intimately connected with a great advancement in the growth
and development of consciousness and of its organ, the brain. But even
when the pupil has got his "certificate of maturity" his consciousness
is still far from mature; it is then that his "world-consciousness"
first begins to develop, in his manifold relations with the outer
world. Then, in the third decade, we have the full maturity of rational
thought and consciousness, which, in cases of normal development, yield
their ripe fruits during the next three decades. The slow, gradual
degeneration of the higher mental powers, which characterizes senility,
usually sets in at the commencement of the seventh decade--sometimes
earlier, sometimes later. Memory, receptiveness, and interest in
particular objects gradually decay; though productivity, mature
consciousness, and philosophic interest in general truths often remain
for many years longer.
The individual development of consciousness in earlier youth proves the
universal validity of the _biogenetic law_; and, indeed, it is still
recognizable in many ways during the later years. In any case, the
ontogenesis of consciousness makes it perfectly clear that it is not
an "immaterial entity," but a physiological function of the brain, and
that it is, consequently, no exception to the general law of substance.
From the fact that consciousness, like all other psychic functions,
is dependent on the normal development of certain organs, and that
it gradually unfolds in the child in proportion to the development
of those organs, we may already conclude that it has arisen in the
animal kingdom by a gradual historical development. Still, however
certain we are of the fact of this natural evolution of consciousness,
we are, unfortunately, not yet in a position to enter more deeply
into the question and construct special hypotheses in elucidation
of it. Palæontology, it is true, gives us a few facts which are not
without significance. For instance, the quantitative and qualitative
development of the brain of the placental mammals during the Tertiary
period is very remarkable. The cavity of many of the fossil skulls of
the period has been carefully examined, and has given us a good deal of
reliable information as to the size, and, to some extent, as to the
structure, of the brain they enclosed. We find, within the limits of
one and the same group (the ungulates, the rodents, or the primates), a
marked advance in the later miocene and pliocene specimens as compared
with the earlier eocene and oligocene representatives of the same stem;
in the former the brain (in proportion to the size of the organism) is
six to eight times as large as in the latter.
Moreover, that highest stage of consciousness, which is reached by man
alone, has been evolved step by step--even by the very progress of
civilization--from a lower condition, as we find illustrated to-day in
the case of uncivilized races. That is easily proved by a comparison
of their languages, which is closely connected with the comparison of
their ideas. The higher the conceptual faculty advances in thoughtful
civilized man, the more qualified he is to detect common features amid
a multitude of details, and embody them in general concepts, and so
much the clearer and deeper does his consciousness become.