SENSATION AND EXPERIENCE.
A careful study of the various theories which have been held
concerning sensation would be of as much interest and importance as
an investigation of any one point in the range of philosophy. In the
theory of a philosopher about sensation we have the reflex of his
fundamental category and the clew to his further doctrine. Sensation
stands on the border-line between the world of nature and the realm of
soul; and every advance in science, every development of philosophy,
leaves its impress in a change in the theory of sensation. Apparently
one of the simplest and most superficial of questions, in reality
it is one of the most difficult and far-reaching. At first sight it
seems as if it were a sufficient account of sensation to say that
an object affects the organ of sense, and thus impresses upon the
mind the quality which it possesses. But this simple statement
arouses a throng of further questions: How is it possible that
one substance,--matter,--should affect another,--mind? How can a
causal relation exist between them? Is the mind passive or active
in this impression? How can an object convey unchanged to the mind
a quality which it possesses? Or is the sensational _quale_ itself
a product of the mind's activity? If so, what is the nature of the
object which excites the sensation? As known, it is only a collection
of sensuous qualities; if these are purely mental, what becomes of
the object? And if there is no object really there, what is it that
excites the sensation? Such questionings might be continued almost
indefinitely; but those given are enough to show that an examination
of the nature and origin of sensation introduces us to the problems
of the relation of intelligence and the world; to the problem of
the ultimate constitution of an object which is set over against a
subject and which affects it; and to the problem of the nature of mind,
which as thus affected from without must be limited in its nature,
but which as bearer of the whole known universe must be in some sense
infinite. If we consider, not the mode of production of sensation,
but its relation to knowledge, we find philosophical schools divided
into two,--Sensationalists, and Rationalists. If we inquire into its
functions, we find that the empiricist sees in it convincing evidence
of the fact that all knowledge originates from a source _extra mentem_;
that the intellectual idealist finds in it evidence of the gradual
transition of nature into spirit; that the ethical idealist, like Kant
and Fichte, sees in it the material of the phenomenal world, which is
necessary in its opposition to the rational sphere in order that there
may occur that conflict of pure law and sensuous impulse which alone
makes morality possible. We thus realize that as we look at the various
aspects of sensation, we are taken into the discussion of ontology, of
the theory of knowledge and of ethics.
Locke virtually recognizes the extreme importance of the doctrine of
sensation, and his second book might almost be entitled "Concerning the
Nature and Products of Sensation." On the other hand, one of the most
characteristic and valuable portions of the reply of Leibniz is in his
development of a theory of sensation which is thoroughly new, except as
we seek for its germs in its thoughts of Plato and Aristotle. According
to Locke, knowledge originates from two sources,--sensation and
reflection. Sensations are "the impressions made on our senses by
outward objects that are extrinsic to the mind." When the mind "comes
to reflect on its own operations about the ideas got by sensation,
and thereby stores itself with a new set of ideas," it gets ideas of
reflection.
If we leave out of account for the present the ideas of reflection,
we find that the ideas which come through sensation have two main
characteristics. First, in having sensations, the mind is passive;
its part is purely receptive. The objects impress themselves upon
the mind, they obtrude into consciousness, whether the mind will or
not. There is a purely external relation existing between sensation
and the understanding. The ideas are offered to the mind, and the
understanding cannot refuse to have them, cannot change them, blot
them out, nor create them, any more than a mirror can refuse, alter,
or obliterate the images which objects produce in it. Sensation,
in short, is a purely passive having of ideas. Secondly, every
sensation is simple. Locke would say of sensations what Hume said of
all ideas,--every distinct sensation is a separate existence. Every
sensation is "uncompounded, containing nothing but one uniform
appearance, not being distinguishable into different ideas." Knowledge
is henceforth a process of compounding, of repeating, comparing, and
uniting sensation. Man's understanding "reaches no further than to
compound and divide the materials that are made to his hand."
It hardly need be said that Locke has great difficulty in keeping up
this thoroughly atomic theory of mind. It is a theory which makes all
relations external; they are, as Locke afterwards says, "superinduced"
upon the facts. It makes it impossible to account for any appearance
of unity and connection among ideas, and Locke quietly, and without
any consciousness of the contradiction involved, introduces certain
inherent relations into the structure of the ideas when he comes to his
constructive work. "Existence and unity are two ideas," he says, "that
are suggested to the understanding by every object without, and every
idea within."
At other places he introduces the idea of quality of a substance,
effect of a cause, continued permanence or identity into a sensation,
as necessary constituents of it; thus making a sensation a unity of
complex elements instead of an isolated bare notion. How far he could
have got on in his account of knowledge without this surreptitious
qualifying of a professedly simple existence, may be seen by asking
what would be the nature of a sensation which did not possess existence
and unity, and which was not conceived as the quality of a thing or as
the effect of an external reality.
This digression has been introduced at this point because the next
character of a sensation which Locke discusses is its objective
character,--its relation to the object which produces it. To
discourse of our ideas intelligibly, he says, it will be convenient
to distinguish them as they are ideas in our minds and as they are
modifications of matter in the bodies that cause them. In other
words, he gives up all thought of considering ideas as simply mental
modifications, and finds it necessary to take them in their relations
to objects.
Taking them in this way, he finds that they are to be divided into
two classes, of which one contains those ideas that are copies and
resemblances of qualities in the objects, ideas "which are really in
the object, whether we take notice of them or no,"--in which case we
have an idea of the thing as it is in itself; while the other class
contains those which are in no way resemblances of the objects which
produce them, "having no more similitude than the idea of pain and of a
sword." The former are primary qualities, and are solidity, extension,
figure, motion or rest, and number; while the secondary qualities
are colors, smells, and tastes. The former ideas are produced by
impulse of the bodies themselves, which simply effect a transference
of their qualities over into the mind; while the secondary qualities
are arbitrarily annexed by the power of God to the objects which excite
them.
It will be noticed that there are two elements which make the sensation
of Locke what it is. With reference to its _production_, it is the
effect which one substance, matter, has upon another substance,
mind, which is unlike it in nature, and between which whatever
relations exist, are thoroughly incomprehensible, so that, indeed,
their connections with each other can be understood only by recourse
to a _tertium quid_, an omnipotent power which can arbitrarily produce
such collocations as please it. With reference to its _function_, it
is the isolated and "simple" (that is, non-relational) element out
of which all actual forms of knowledge are made by composition and
re-arrangement.
Leibniz, without entering into explicit criticism of just these two
points, develops his own theory with reference to them. To Leibniz,
reality constitutes a system; that is, it is of such a nature that
its various portions have an essential and not merely external
relation to one another. Sensation is of course no exception. It is
not a mere accident, nor yet a supernatural yoking of things naturally
opposed. It has a meaning in that connection of things which constitute
the universe. It contributes to the significance of the world. It
is one way in which those activities which make the real express
themselves. It has its place or reason in the totality of things, and
this whether we consider its origin or its position with regard to
knowledge. In a word, while the characteristic of Locke's theory is
that he conceives sensation as in external relation both to reality,
as mechanically produced by it, and to knowledge, as being merely
one of the atomic elements which may enter into a compound, Leibniz
regards reality as organic to sensation, and this in turn as organic
to knowledge. We have here simply an illustration of the statement
with which we set out; namely, that the treatment of sensation always
reflects the fundamental philosophical category of the philosopher.
All reality exists in the form of monads; monads are simple substances
whose nature is action; this action consists in representing, according
to a certain law of succession, the universe. Various monads have
various degrees of activity; that is, of the power of reflecting
the world. So much of Leibniz's general philosophical attitude it is
necessary to recall, to understand what he means by "sensation." The
generic name which is applied to this mirroring activity of the monads
is "perception," which, as Leibniz often says, is to be carefully
distinguished from apperception, which is the representation become
conscious. Perception may be defined, therefore, as the inclusion of
the many or multiform (the world of objects) in a unity (the simple
substance). It was the great defect of previous philosophy that it
"considered only spirits or self-conscious beings as souls," and
had consequently recognized only conscious perceptions. It had been
obliged, therefore, to make an impassable gulf between mind and matter,
and sensations were thus rendered inexplicable. But Leibniz finds his
function as a philosopher in showing that these problems, which seem
insoluble, arise when we insist upon erecting into actual separations
or differences of kind what really are only stages of development
or differences of degree. A sensation is not an effect which one
substance impresses upon another because God pleased that it should, or
because of an incomprehensible incident in the original constitution of
things. It is a higher development of that representative power which
belongs to every real being.
Certain monads reach a state of development, or manifestation of
activity, which is characterized by the possession of distinct
organs. Such monads may be called, in a pre-eminent sense, "souls,"
and include all the higher animals as well as man. This possession of
differentiated organs finds its analogue in the internal condition of
the monad. What appears externally as an organ of sense appears ideally
as a conscious representative state which we call "sensation." "When,"
Leibniz says, "the monad has its organs so developed that there
is relief and differentiation in the impressions received, and
consequently in the perceptions which represent them, we have feeling
or sensation; that is, a perception accompanied by memory," to which
at other times he adds "attention." Life, he says, "is a perceptive
principle; the soul is sensitive life; mind is rational soul." And
again he says in substance that when the soul begins to have interests,
and to regard one representation as of more value than others, it
introduces relief into its perceptions, and those which stand out are
called "sensations."
This origin of sensations as higher developments of the representative
activities of a monad conditions their relation to further processes
of knowledge. The sensations are confused knowledge; they are ideas
in their primitive and most undifferentiated form. They constitute,
as Leibniz somewhere says, the vertigo of the conscious life. In every
sentient organism multitudes of sensations are constantly thronging in
and overpowering its distinct consciousness. The soul is so flooded
with ideas of everything in the world which has any relation to
its body that it has distinct ideas of nothing. Higher knowledge,
then, does not consist in compounding these sensations; that would
literally make confusion worse confounded. It consists in introducing
distinctness into the previously confused sensations,--in finding out
what they mean; that is, in finding out their bearings, what they point
to, and how they are related. Knowledge is not an external process
performed upon the sensations, it is the development of their internal
content.
It follows, therefore, that sensation is organic to all forms of
knowledge whatever. The monad, which is pure activity, that which
culminates the scale of reality, has no confused ideas, and to it
all knowledge is eternally rational, having no sensible traces about
it. But every other monad, having its activity limited, has ideas
which come to it at first in a confused way, and which its activity
afterwards differentiates. Thus it is that Leibniz can agree so
heartily with the motto of the Sensationalist school,--that there is
nothing in the intellect which was not first in the sensory. But
Leibniz uses this phrase as Aristotle would have done, having
in mind the distinction between potentiality and actuality. _In
posse_, sensation is all knowledge; but only _in posse_. And he, like
Aristotle, interprets the relation between potentiality and actuality
as one of a difference of activity. The potential is that which
becomes real through a dynamic process. The actual is capacity plus
action. Sensation, in short, is spiritual activity in an undeveloped
and hence partial and limited condition. It is not, as Locke would have
it, the real factor in all knowledge.
The marks of sensation which Locke lays down,--their passivity, their
simplicity, their position as the real element in knowledge,--Leibniz
either denies, therefore, or accepts in a sense different from that of
Locke. Strictly speaking, sensation is an activity of the mind. There
are no windows through which the soul receives impressions. Pure
passivity of any kind is a myth, a scholastic fiction. Sensation is
developed from the soul within; it is the activity of reality made
manifest to itself. It is a higher kind of action than anything we find
in minerals or in plants. If we look at sensation ideally, however,
that is, according to the position which it holds in the system
of knowledge, it is properly regarded as passive. It represents the
limitation, the unrealized (that is, the non-active) side of spiritual
life.
"Efficient causality" is a term which has its rightful and legitimate
use in physical science. Simply from the scientific point of view
we are correct in speaking of objects as affecting the body, and the
body, through its nervous system, as affecting the soul and producing
sensations. But philosophy does not merely use categories, it explains
them. And Leibniz contends that to explain the category of causality
in a mechanical sense, to understand by it physical influence actually
transferred from one thing to another, is to make the idea inexplicable
and irrational. The true meaning of causality is ideal. It signifies
the relative positions which the objects concerned have in the
harmonious system of reality. The body that is higher in the scale
impresses the other; that is to say, it dominates it or gives its
law. There is no energy or quality which passes physically from one
to the other. But one monad, as higher in the stage of development
than another, makes an ideal demand upon that one. It places before
the other its own more real condition. The less-developed monad, since
its whole activity consists in representing the universe of reality,
answers to this demand by developing the corresponding quality in
itself. The category of harmonious or co-operative action is thus
substituted for that of external and mechanical influence. Physical
causality when given a philosophic interpretation means organic
development. The reality of a higher stage is the more active: the
more active has a greater content in that it mirrors the universe more
fully; it manifests accordingly more of the law of the universe, and
hence has an ideal domination over that which is lower in the scale. It
is actually (that is, in activity) what the other is potentially. But
as the entire existence of the latter is in representing or setting
forth the relations which make the world, its activity is aroused to a
corresponding production. Hence the former is called "cause," and the
latter "effect."
This introduces us to the relation of soul and body, or, more generally
stated, to the relation of mind and matter. It is the theory of
co-operation, of harmonious activity, which Leibniz substitutes for
the theory which Descartes had formulated, according to which there
are two opposed substances which can affect each other only through
the medium of a _deus ex machina_. Locke, on the other hand, took the
Cartesian principle for granted, and thus enveloped himself in all the
difficulties which surround the question of "mind and matter." Locke
wavers between two positions, one of which is that there are two
unknown substances,--the soul and the object in itself,--which, coming
in contact, produce sensations; while the other takes the hypothetical
attitude that there may be but one substance,--matter,--and that
God, out of the plenitude of his omnipotence, has given matter a
capacity which does not naturally belong to it,--that of producing
sensations. In either case, however, the final recourse is to the
arbitrary power of God. There is no natural--that is, intrinsic and
explicable--connection between the sensation and that which produces
it. Sensation occupied the hard position which the mechanical school
of to-day still allots it. It is that "inexplicable," "mysterious,"
"unaccountable" link between the domains of matter and mind of which no
rational account can be given, but which is yet the source of all that
we know about matter, and the basis of all that is real in the mind!
Leibniz, recognizing that reality is an organic whole,--not two parts
with a chasm between them,--says that "God does not arbitrarily give
substances whatever qualities may happen, or that he may arbitrarily
determine, but only such as are natural; that is, such as are
related to one another in an _explicable_ way as modifications of
the substance." Leibniz feels sure that to introduce the idea of the
inexplicable, the purely supernatural, into the natural is to give up
all the advantages which the modern mechanical theory had introduced,
and to relapse into the meaningless features of scholasticism. If the
"supernatural"--that is, the essentially inexplicable--is introduced
in this one case, why should it not be in others; why should we not
return outright to the "fanatic philosophy which explains all facts by
simply attributing them to God immediately or by way of miracle, or to
the barbarian philosophy, which explains phenomena by manufacturing,
_ad hoc_, occult qualities or faculties, seemingly like little
demons or spirits capable of performing, without ceremony, whatever
is required,--as if watches marked time by their horodeictic power,
without wheels, and mills ground grain, without grindstones, by their
fractive power"? In fact, says Leibniz, by introducing the inexplicable
into our _explanations_ "we fall into something worse than occult
qualities,--we give up philosophy and reason; we open asylums for
ignorance and laziness, holding not only that there are qualities which
we do not understand (there are, indeed, too many such), but qualities
which the greatest intelligence, if God gave it all the insight
possible, could not understand,--that is, such as are _in themselves_
without rhyme or reason. And indeed it would be a thing without
rhyme or reason that God should perform miracles in the ordinary
course of nature." And regarding the whole matter of introducing the
inconceivable and the inexplicable into science, he says that "while
the conception of men is not the measure of God's power, their capacity
of conception is the measure of _nature's_ power, since everything
occurring in the natural order is capable of being understood by the
created intelligence." Such being the thought of Leibniz regarding the
virtual attempt to introduce in his day the unknowable into philosophy,
it is evident that he must reject, from the root up, all theories of
sensation which, like Locke's, make it the product of the inexplicable
intercourse of two substances.
For this doctrine, then, Leibniz substitutes that of an infinite number
of substances, all of the same kind, all active, all developing from
within, all conspiring to the same end, but of various stages of
activity, or bearing various relations of completeness to the one end.
Indeed, one and the same monad has various degrees of activity in
itself; that is, it represents more or less distinctly the universe
according to its point of view. Its point of view requires of it, of
course, primarily, a representation of that which is about it. Thus
an infinity of states arises, each corresponding to some one of the
multitude of objects surrounding the monad. The soul has no control,
no mastery, over these states. It has to take them as they come; with
regard to them, the soul appears passive. It appears so because it does
not as yet clearly distinguish them. It does not react upon them and
become conscious of their meaning or thoroughly rational character. We
shall afterwards see that "matter" is, with Leibniz, simply this
passive or confused side of monads. It is the monad so far as it has
not brought to light the rational activity which is immanent in it. At
present we need only notice that the body is simply the part of matter
or of passivity which limits the complete activity of any monad. So
Leibniz says, "in so far as the soul has perfection, it has distinct
thoughts, and God has accommodated the body to the soul. So far as it
is imperfect and its perceptions are confused, God has accommodated the
soul to the body in such a way that the soul lets itself be inclined by
the passions, which are born from corporeal representations. It is by
its confused thoughts (sensations) that the soul represents the bodies
about it," just as, we may add, its distinct thoughts represent the
monads or souls about it, and, in the degree of their distinctness,
God, the monad which is _purus actus_.
Following the matter into more detail, we may say that since God alone
is pure energy, knowing no limitation, God alone is pure spirit. Every
finite soul is joined to an organic body. "I do not admit," says
Leibniz, "that there are souls entirely separate from matter, nor
created spirits detached from body. . . . It is this body which
the monad represents most distinctly; but since this body expresses the
entire universe by the connection of all matter throughout it, the soul
represents the entire universe in representing the body which belongs
to it most particularly." But according to the principle of continuity
there must be in the least apparent portion of matter still "a universe
of creatures, of souls, of entelechies. There is nothing sterile,
nothing dead in the universe. It is evident from these considerations
that every living body has a dominant entelechy, which is the soul in
that body, but that the members of this living body are again full of
other living beings and souls," which, however, since not of so high
a grade, that is, not representing the universe so fully, appear to be
wholly material and subject to the "dominant" entelechy; namely, to the
one which gives the law to the others by expressing more adequately
the idea at which they only confusedly aim. Owing to the constant
change of activity, however, these particles do not remain in constant
subordination to the same entelechy (that is, do not form parts of the
same body), but pass on to higher or lower degrees of "evolution,"
and have their places taken by others undergoing similar processes
of change. Thus "all bodies are in a perpetual flux, like rivers,
with parts continually leaving and entering in." Or, interpreting
this figurative language, each monad is continually, in its process
of development, giving law to new and less developed monads, which
therefore appear as its body. The nature of matter in itself, and of
its phenomenal manifestation in the body, are, however, subjects which
find no explanation here, and which will demand explanation in another
chapter.
We may sum up Leibniz's theory of sensation by saying that it is a
representative state developed by the self-activity of the soul; that
in itself it is a confused or "involved" grade of activity, and in
its relation to the world represents the confused or passive aspects
of existence; that this limitation of the monad constitutes matter,
and in its necessary connection with the monad constitutes the body
which is always joined to the finite soul; that to this body are joined
in all cases an immense number of monads, whose action is subordinate
to that of this dominant monad, and that it is the collection of these
which constitute the visible animal body. Thus if we look at sensation
with regard to the monad which possesses it, it is a product of the
body of the monad; if we look at it with reference to other monads,
it represents or reflects their passive or material side. This is
evidently one aspect again of the pre-established harmony,--an aspect
in which some of the narrower of Leibniz's critics have seen the whole
meaning of the doctrine exhausted. It is, however, simply one of the
many forms in which the harmony, the union of spiritual and mechanical,
ideal and material, meets us. In truth, while in other systems the fact
of sensation is a fact demanding some artificial mode of reconciling
"mind" and "matter," or is else to be accepted as an inexplicable fact,
in the system of Leibniz it is itself evidence that the spiritual
and the mechanical are not two opposed kinds of existence, but are
organically united. It is itself the manifestation of the harmony
of the ideal and the material, not something which requires that
a factitious theory be invented for explaining their appearance of
harmony. Sensation has within itself the ideal element, for it is the
manifestation, in its most undeveloped form, of the spiritual meaning
of the universe. It has a mechanical element, for it expresses the
limitation, the passivity, of the monad.
It is from this standpoint that Leibniz criticises what Locke says
about the relation of sensations to the objects which produce
them. Leibniz holds that all our sensations have a definite and
natural connection with the qualities of objects,--the "secondary"
as well as the "primary." They all represent certain properties of the
object. Even the pain which the thrust of a needle gives us, while it
does not resemble anything in the needle, does in some way represent
or resemble motions going on in our body. This resemblance is not
necessarily one of exact form, but just as the ellipse, hyperbola,
and parabola are projections of the circle in the sense that there
is a natural and fixed law of connection between them, so that every
point of one corresponds by a certain relation with every point of the
other, so the resemblance between the sensation and the quality of the
object is always in the form of a fixed law of order, which, however
unknown to us it may now be, is capable of being found out. If we are
to make any distinction between "secondary" and "primary" sensations,
it should be not that one presents qualities that are in the objects,
and the other affections which exist only in us, but that the primary
sensations (of number, form, size, etc.) represent the qualities in
a distinct way, appealing to the rational activity of intelligence,
while the secondary represent the qualities in a confused way, a way
not going beyond the effect upon the mind into relations, that is, into
distinct knowledge.
This brings regularly before us the question of the relation of
sensations to knowledge. We have seen enough already to know that
Leibniz does not believe that knowledge begins with the simple (that
is, unrelated), and then proceeds by a process of compounding. The
sensation is not simple to Leibniz, but thoroughly complex, involving
confusedly within itself all possible relations. As relations are
brought forth into distinct light out of this confusion, knowledge
ends rather than begins with the simple. And again it is evident that
Leibniz cannot believe that knowledge begins and ends in experience,
in the sense in which both himself and Locke use the word; namely, as
meaning the combination and succession of impressions.
"Experience," as they use the term, consists in sensations and their
association,--"consecution" as Leibniz calls it. Experience is the
stage of knowledge reached by animals, and in which the majority
of men remain,--and indeed all men in the greater part of their
knowledge. Leibniz takes just the same position regarding the larger
part of our knowledge which Hume takes regarding it all. It consists
simply in associations of such a nature that when one part recurs
there is a tendency to expect the recurrence of the other member. It
resembles reason, but it is based on the accidental experience of
events in a consecutive order, and not on knowledge of their causal
connection. We all expect the sun to rise to-morrow; but with all of
us, excepting the astronomer, such expectation is purely "empirical,"
being based on the images of past experiences which recur. The
astronomer, however, sees into the grounds, that is, the reasons, of
the expectation, and hence his knowledge is rational.
Thus we have two grades of knowledge,--one empirical, consisting
of knowledge of facts; the other rational, being of the truths
of reason. The former is contingent and particular, the latter is
necessary and universal. Leibniz insists, with a pertinacity which
reminds us of Kant, that "experience" can give instances or examples
only, and that the fact that anything has happened in a given way
any number of times in the past, can give no assurance that it will
continue to do so in the future. There is nothing in the nature
of the case which renders its exact opposite impossible. But a
rational truth is necessary, for its opposite is impossible, being
irrational or meaningless. This may not always be evident in the
case of a complex rational truth; but if it be analyzed into simpler
elements, as a geometrical proposition into definitions, axioms, and
postulates, the absurdity of its opposite becomes evident. Sensation,
in conclusion, is the having of confused ideas,--ideas corresponding
to matter. Experience is the association of these confused ideas, and
their association according to their accidental juxtaposition in the
life of the soul. It therefore is not only thoroughly sensible, but is
also phenomenal. Its content is sensations; its form is contingent and
particular consecution. Both form and content, accordingly, need to be
reconstructed if they are to be worthy of the name of science or of
knowledge. This is the position which Leibniz assumes as against the
empiricist, Locke. The details of this reconstruction, its method and
result, we must leave till we come in the course of the argument again
to the subject of knowledge.