hitherto been treading, leads through doubt to that critical Idealism
which lies at the heart of modern metaphysical thought. But the
"Discourse" shows us another, and apparently very different, path, which
leads, quite as definitely, to that correlation of all the phænomena of
the universe with matter and motion, which lies at the heart of modern
physical thought, and which most people call Materialism.
The early part of the seventeenth century, when Descartes reached
manhood, is one of the great epochs of the intellectual life of mankind.
At that time, physical science suddenly strode into the arena of public
and familiar thought, and openly challenged, not only Philosophy and the
Church, but that common ignorance which passes by the name of Common
Sense. The assertion of the motion of the earth was a defiance to all
three, and Physical Science threw down her glove by the hand of Galileo.
It is not pleasant to think of the immediate result of the combat; to
see the champion of science, old, worn, and on his knees before the
Cardinal Inquisitor, signing his name to what he knew to be a lie. And,
no doubt, the Cardinals rubbed their hands as they thought how well they
had silenced and discredited their adversary. But two hundred years have
passed, and however feeble or faulty her soldiers, Physical Science sits
crowned and enthroned as one of the legitimate rulers of the world of
thought. Charity children would be ashamed not to know that the earth
moves; while the Schoolmen are forgotten; and the Cardinals--well, the
Cardinals are at the oecumenical Council, still at their old business
of trying to stop the movement of the world.
As a ship, which having lain becalmed with every stitch of canvas set,
bounds away before the breeze which springs up astern, so the mind of
Descartes, poised in equilibrium of doubt, not only yielded to the full
force of the impulse towards physical science and physical ways of
thought, given by his great contemporaries, Galileo and Harvey, but shot
beyond them; and anticipated, by bold speculation, the conclusions,
which could only be placed upon a secure foundation by the labours of
generations of workers.
Descartes saw that the discoveries of Galileo meant that the remotest
parts of the universe were governed by mechanical laws; while those of
Harvey meant that the same laws presided over the operations of that
portion of the world which is nearest to us, namely, our own bodily
frame. And crossing the interval between the centre and its vast
circumference by one of the great strides of genius, Descartes sought to
resolve all the phænomena of the universe into matter and motion, or
forces operating according to law.[71] This grand conception, which is
sketched in the "Discours," and more fully developed in the "Principes"
and in the "Traité de l'Homme," he worked out with extraordinary power
and knowledge; and with the effect of arriving, in the last-named essay,
at that purely mechanical view of vital phænomena towards which modern
physiology is striving.
Let us try to understand how Descartes got into this path, and why it
led him where it did. The mechanism of the circulation of the blood had
evidently taken a great hold of his mind, as he describes it several
times, at much length. After giving a full account of it in the
"Discourse," and erroneously describing the motion of the blood, not to
the contraction of the walls of the heart, but to the heat which he
supposes to be generated there, he adds:--
"This motion, which I have just explained, is as much the necessary
result of the structure of the parts which one can see in the
heart, and of the heat which one may feel there with one's fingers,
and of the nature of the blood, which may be experimentally
ascertained; as is that of a clock of the force, the situation, and
the figure, of its weight and of its wheels."
But if this apparently vital operation were explicable as a simple
mechanism, might not other vital operations be reducible to the same
category? Descartes replies without hesitation in the affirmative.
"The animal spirits," says he, "resemble a very subtle fluid, or a
very pure and vivid flame, and are continually generated in the
heart, and ascend to the brain as to a sort of reservoir. Hence
they pass into the nerves and are distributed to the muscles,
causing contraction, or relaxation, according to their quantity."
Thus, according to Descartes, the animal body is an automaton, which is
competent to perform all the animal functions in exactly the same way as
a clock or any other piece of mechanism. As he puts the case himself:--
"In proportion as these spirits [the animal spirits] enter the
cavities of the brain, they pass thence into the pores of its
substance, and from these pores into the nerves; where, according
as they enter, or even only tend to enter, more or less, into one
than into another, they have the power of altering the figure of
the muscles into which the nerves are inserted, and by this means
of causing all the limbs to move. Thus, as you may have seen in the
grottoes and the fountains in royal gardens, the force with which
the water issues from its reservoir is sufficient to move various
machines, and even to make them play instruments, or pronounce
words according to the different disposition of the pipes which
lead the water.
"And, in truth, the nerves of the machine which I am describing may
very well be compared to the pipes of these waterworks; its muscles
and its tendons to the other various engines and springs which seem
to move them; its animal spirits to the water which impels them, of
which the heart is the fountain; while the cavities of the brain
are the central office. Moreover, respiration and other such
actions as are natural and usual in the body, and which depend on
the course of the spirits, are like the movements of a clock, or of
a mill, which may be kept up by the ordinary flow of the water.
"The external objects which, by their mere presence, act upon the
organs of the senses; and which, by this means, determine the
corporal machine to move in many different ways, according as the
parts of the brain are arranged, are like the strangers who,
entering into some of the grottoes of these waterworks,
unconsciously cause the movements which take place in their
presence. For they cannot enter without treading upon certain
planks so arranged that, for example, if they approach a bathing
Diana, they cause her to hide among the reeds; and if they attempt
to follow her, they see approaching a Neptune, who threatens them
with his trident; or if they try some other way, they cause some
monster who vomits water into their faces, to dart out; or like
contrivances, according to the fancy of the engineers who have made
them. And lastly, when the _rational soul_ is lodged in this
machine, it will have its principal seat in the brain, and will
take the place of the engineer, who ought to be in that part of the
works with which all the pipes are connected, when he wishes to
increase, or to slacken, or in some way to alter, their
movements."[72]
And again still more strongly:--
"All the functions which I have attributed to this machine (the
body), as the digestion of food, the pulsation of the heart and of
the arteries; the nutrition and the growth of the limbs;
respiration, wakefulness, and sleep; the reception of light,
sounds, odours, flavours, heat, and such like qualities, in the
organs of the external senses; the impression of the ideas of these
in the organ of common sense and in the imagination; the retention,
or the impression, of these ideas on the memory; the internal
movements of the appetites and the passions; and lastly, the
external movements of all the limbs, which follow so aptly, as well
the action of the objects which are presented to the senses, as the
impressions which meet in the memory, that they imitate as nearly
as possible those of a real man:[73] I desire, I say, that you
should consider that these functions in the machine naturally
proceed from the mere arrangement of its organs, neither more nor
less than do the movements of a clock, or other automaton, from
that of its weights and its wheels; so that, so far as these are
concerned, it is not necessary to conceive any other vegetative or
sensitive soul, nor any other principle of motion, or of life, than
the blood and the spirits agitated by the fire which burns
continually in the heart, and which is no wise essentially
different from all the fires which exist in inanimate bodies."[74]
The spirit of these passages is exactly that of the most advanced
physiology of the present day; all that is necessary to make them
coincide with our present physiology in form, is to represent the
details of the working of the animal machinery in modern language, and
by the aid of modern conceptions.
Most undoubtedly, the digestion of food in the human body is a purely
chemical process; and the passage of the nutritive parts of that food
into the blood, a physical operation. Beyond all question, the
circulation of the blood is simply a matter of mechanism, and results
from the structure and arrangement of the parts of the heart and
vessels, from the contractility of those organs, and from the
regulation of that contractility by an automatically acting nervous
apparatus. The progress of physiology has further shown, that the
contractility of the muscles and the irritability of the nerves are
purely the results of the molecular mechanism of those organs; and that
the regular movements of the respiratory, alimentary, and other internal
organs are governed and guided, as mechanically, by their appropriate
nervous centres. The even rhythm of the breathing of every one of us
depends upon the structural integrity of a particular region of the
medulla oblongata, as much as the ticking of a clock depends upon the
integrity of the escapement. You may take away the hands of a clock and
break up its striking machinery, but it will still tick; and a man may
be unable to feel, speak, or move, and yet he will breathe.
Again, in entire accordance with Descartes' affirmation, it is certain
that the modes of motion which constitute the physical basis of light,
sound, and heat, are transmuted into affections of nervous matter by the
sensory organs. These affections are, so to speak, a kind of physical
ideas, which are retained in the central organs, constituting what might
be called physical memory, and may be combined in a manner which answers
to association and imagination, or may give rise to muscular
contractions, in those "reflex actions" which are the mechanical
representatives of volitions.
Consider what happens when a blow is aimed at the eye.[75] Instantly,
and without our knowledge or will, and even against the will, the
eyelids close. What is it that happens? A picture of the rapidly
advancing fist is made upon the retina at the back of the eye. The
retina changes this picture into an affection of a number of the fibres
of the optic nerve; the fibres of the optic nerve affect certain parts
of the brain; the brain, in consequence, affects those particular fibres
of the seventh nerve which go to the orbicular muscle of the eyelids;
the change in these nerve-fibres causes the muscular fibres to change
their dimensions, so as to become shorter and broader; and the result is
the closing of the slit between the two lids, round which these fibres
are disposed. Here is a pure mechanism, giving rise to a purposive
action, and strictly comparable to that by which Descartes supposes his
waterwork Diana to be moved. But we may go further, and inquire whether
our volition, in what we term voluntary action, ever plays any other
part than that of Descartes' engineer, sitting in his office, and
turning this tap or the other, as he wishes to set one or another
machine in motion, but exercising no direct influence upon the movements
of the whole.
Our voluntary acts consist of two parts: firstly, we desire to perform a
certain action; and, secondly, we somehow set a-going a machinery which
does what we desire. But so little do we directly influence that
machinery, that nine-tenths of us do not even know its existence.
Suppose one wills to raise one's arm and whirl it round. Nothing is
easier. But the majority of us do not know that nerves and muscles are
concerned in this process; and the best anatomist among us would be
amazingly perplexed, if he were called upon to direct the succession,
and the relative strength, of the multitudinous nerve-changes, which are
the actual causes of this very simple operation.
So again in speaking. How many of us know that the voice is produced in
the larynx, and modified by the mouth? How many among these instructed
persons understand how the voice is produced and modified? And what
living man, if he had unlimited control over all the nerves supplying
the mouth and larynx of another person, could make him pronounce a
sentence? Yet, if one has anything to say, what is easier than to say
it? We desire the utterance of certain words: we touch the spring of the
word-machine, and they are spoken. Just as Descartes' engineer, when he
wanted a particular hydraulic machine to play, had only to turn a tap,
and what he wished was done. It is because the body is a machine that
education is possible. Education is the formation of habits, a
superinducing of an artificial organization upon the natural
organization of the body; so that acts, which at first required a
conscious effort, eventually became unconscious and mechanical. If the
act which primarily requires a distinct consciousness and volition of
its details, always needed the same effort, education would be an
impossibility.
According to Descartes, then, all the functions which are common to man
and animals are performed by the body as a mere mechanism, and he looks
upon consciousness as the peculiar distinction of the "_chose
pensante_," of the "rational soul," which in man (and in man only, in
Descartes' opinion) is superadded to the body. This rational soul he
conceived to be lodged in the pineal gland, as in a sort of central
office; and, here, by the intermediation of the animal spirits, it
became aware of what was going on in the body, or influenced the
operations of the body. Modern physiologists do not ascribe so exalted
a function to the little pineal gland, but, in a vague sort of way, they
adopt Descartes' principle, and suppose that the soul is lodged in the
cortical part of the brain--at least this is commonly regarded as the
seat and instrument of consciousness.
Descartes has clearly stated what he conceived to be the difference
between spirit and matter. Matter is substance which has extension, but
does not think; spirit is substance which thinks, but has no extension.
It is very hard to form a definite notion of what this phraseology
means, when it is taken in connexion with the location of the soul in
the pineal gland; and I can only represent it to myself as signifying
that the soul is a mathematical point, having place but not extension,
within the limits of the pineal gland. Not only has it place, but it
must exert force; for, according to the hypothesis, it is competent,
when it wills, to change the course of the animal spirits, which consist
of matter in motion. Thus the soul becomes a centre of force. But, at
the same time, the distinction between spirit and matter vanishes;
inasmuch as matter, according to a tenable hypothesis, may be nothing
but a multitude of centres of force. The case is worse if we adopt the
modern vague notion that consciousness is seated in the grey matter of
the cerebrum, generally; for, as the grey matter has extension, that
which is lodged in it must also have extension. And thus we are led, in
another way, to lose spirit in matter.
In truth, Descartes' physiology, like the modern physiology of which it
anticipates the spirit, leads straight to Materialism, so far as that
title is rightly applicable to the doctrine that we have no knowledge
of any thinking substance, apart from extended substance; and that
thought is as much a function of matter as motion is. Thus we arrive at
the singular result that, of the two paths opened up to us in the
"Discourse upon Method," the one leads, by way of Berkeley and Hume, to
Kant and Idealism; while the other leads, by way of De La Mettrie and
Priestley, to modern physiology and Materialism.[76] Our stem divides
into two main branches, which grow in opposite ways, and bear flowers
which look as different as they can well be. But each branch is sound
and healthy, and has as much life and vigour as the other.
If a botanist found this state of things in a new plant, I imagine that
he might be inclined to think that his tree was monoecious--that the
flowers were of different sexes, and that, so far from setting up a
barrier between the two branches of the tree, the only hope of fertility
lay in bringing them together. I may be taking too much of a
naturalist's view of the case, but I must confess that this is exactly
my notion of what is to be done with metaphysics and physics. Their
differences are complementary, not antagonistic; and thought will never
be completely fruitful until the one unites with the other. Let me try
to explain what I mean. I hold, with the Materialist, that the human
body, like all living bodies, is a machine, all the operations of which
will, sooner or later, be explained on physical principles. I believe
that we shall, sooner or later, arrive at a mechanical equivalent of
consciousness, just as we have arrived at a mechanical equivalent of
heat. If a pound weight falling through a distance of a foot gives rise
to a definite amount of heat, which may properly be said to be its
equivalent; the same pound weight falling through a foot on a man's hand
gives rise to a definite amount of feeling, which might with equal
propriety be said to be its equivalent in consciousness.[77] And as we
already know that there is a certain parity between the intensity of a
pain and the strength of one's desire to get rid of that pain; and
secondly, that there is a certain correspondence between the intensity
of the heat, or mechanical violence, which gives rise to the pain, and
the pain itself; the possibility of the establishment of a correlation
between mechanical force and volition becomes apparent. And the same
conclusion is suggested by the fact that, within certain limits, the
intensity of the mechanical force we exert is proportioned to the
intensity of our desire to exert it.
Thus I am prepared to go with the Materialists wherever the true pursuit
of the path of Descartes may lead them; and I am glad, on all occasions,
to declare my belief that their fearless development of the
materialistic aspect of these matters has had an immense, and a most
beneficial, influence upon physiology and psychology. Nay more, when
they go farther than I think they are entitled to do--when they
introduce Calvinism into science and declare that man is nothing but a
machine, I do not see any particular harm in their doctrines, so long as
they admit that which is a matter of experimental fact--namely, that it
is a machine capable of adjusting itself within certain limits.
I protest that if some great Power would agree to make me always think
what is true and do what is right, on condition of being turned into a
sort of clock and wound up every morning before I got out of bed, I
should instantly close with the offer. The only freedom I care about is
the freedom to do right; the freedom to do wrong I am ready to part with
on the cheapest terms to any one who will take it of me. But when the
Materialists stray beyond the borders of their path and begin to talk
about there being nothing else in the universe but Matter and Force and
Necessary Laws, and all the rest of _their_ "grenadiers," I decline to
follow them. I go back to the point from which we started, and to the
other path of Descartes. I remind you that we have already seen clearly
and distinctly, and in a manner which admits of no doubt, that all our
knowledge is a knowledge of states of consciousness. "Matter" and
"Force" are, so far as we can know, mere names for certain forms of
consciousness. "Necessary" means that of which we cannot conceive the
contrary. "Law" means a rule which we have always found to hold good,
and which we expect always will hold good. Thus it is an indisputable
truth that what we call the material world is only known to us under the
forms of the ideal world; and, as Descartes tells us, our knowledge of
the soul is more intimate and certain than our knowledge of the body.
If I say that impenetrability is a property of matter, all that I can
really mean is that the consciousness I call extension, and the
consciousness I call resistance, constantly accompany one another. Why
and how they are thus related is a mystery. And if I say that thought is
a property of matter, all that I can mean is that, actually or possibly,
the consciousness of extension and that of resistance accompany all
other sorts of consciousness. But, as in the former case, why they are
thus associated is an insoluble mystery.
From all this it follows that what I may term legitimate materialism,
that is, the extension of the conceptions and of the methods of physical
science to the highest as well as the lowest phenomena of vitality, is
neither more nor less than a sort of shorthand Idealism; and Descartes'
two paths meet at the summit of the mountain, though they set out on
opposite sides of it.
The reconciliation of physics and metaphysics lies in the acknowledgment
of faults upon both sides; in the confession by physics that all the
phænomena of nature are, in their ultimate analysis, known to us only as
facts of consciousness; in the admission by metaphysics, that the facts
of consciousness are, practically, interpretable only by the methods and
the formulæ of physics: and, finally, in the observance by both
metaphysical and physical thinkers of Descartes' maxim--assent to no
proposition the matter of which is not so clear and distinct that it
cannot be doubted.
When you did me the honour to ask me to deliver this address, I confess
I was perplexed what topic to select. For you are emphatically and
distinctly a _Christian_ body; while science and philosophy, within the
range of which lie all the topics on which I could venture to speak, are
neither Christian, nor Unchristian, but are Extrachristian, and have a
world of their own, which, to use language which will be very familiar
to your ears just now, is not only "unsectarian," but is altogether
"secular." The arguments which I have put before you to-night, for
example, are not inconsistent, so far as I know, with any form of
theology.
After much consideration, I thought that I might be most useful to you,
if I attempted to give you some vision of this Extrachristian world, as
it appears to a person who lives a good deal in it; and if I tried to
show you by what methods the dwellers therein try to distinguish truth
from falsehood, in regard to some of the deepest and most difficult
problems that beset humanity, "in order to be clear about their actions,
and to walk surefootedly in this life," as Descartes says.
It struck me that if the execution of my project came anywhere near the
conception of it, you would become aware that the philosophers and the
men of science are not exactly what they are sometimes represented to
you to be; and that their methods and paths do not lead so
perpendicularly downwards as you are occasionally told they do. And I
must admit, also, that a particular and personal motive weighed with
me,--namely, the desire to show that a certain discourse, which brought
a great storm about my head some time ago, contained nothing but the
ultimate development of the views of the father of modern philosophy. I
do not know if I have been quite wise in allowing this last motive to
weigh with me. They say that the most dangerous thing one can do in a
thunderstorm is to shelter oneself under a great tree, and the history
of Descartes' life shows how narrowly he escaped being riven by the
lightnings, which were more destructive in his time than in ours.