thing conjectural, are without use in philosophy, it would be absurd
to affirm, since every inquiry may, in that wide sense, be said to
pre-suppose them, and must always pre-suppose them if the inquiry have
any object. They are of use, however, not as superseding investigation,
but as directing investigation to certain objects,--not as telling
us, what we are to believe, but as pointing out to us what we are to
endeavour to ascertain. An hypothesis, in this view of it, is nothing
more than a reason for making one experiment or observation rather
than another; and it is evident, that, without some reason of this
kind, as experiment and observations are almost infinite, inquiry
would be altogether profitless. To make experiments, at random, is not
to _philosophize_; it becomes philosophy, only when the experiments
are made with a certain view; and to make them, with any particular
view, is to suppose the presence of something, the operation of which
they will tend either to prove or disprove. When Torricelli, for
example,--proceeding on the observation previously made, by Galileo,
with respect to the limited height to which water could be made to rise
in a pump,--that memorable observation, which demonstrated, at last,
after so many ages of errors, what ought not for a single moment to
have required to be demonstrated; the absurdity of the horror of a void
ascribed to nature--when, proceeding in this memorable observation,
Torricelli made his equally memorable experiment with respect to the
height of the column of mercury supported in an inverted tube, and
found, on comparison of their specific gravities, the columns of
mercury and water to be exactly equiponderant, it is evident that he
was led to the experiment with the mercury by the supposition, that
the rise of fluids _in vacuo_ was occasioned by some counterpressure,
exactly equal to the weight supported, and that the column of mercury,
therefore should be less in height than the column of water, in
the exact inverse ratio of their specific gravities, by which the
counterpressure was to be sustained. To conceive the air, which was
then universally regarded as essentially light, to be not light but
heavy, so as to press on the fluid beneath, was, at that time, to make
as bold a supposition as could be made. It was indeed, a temporary
hypothesis, even when it led to that experimental demonstration of the
fact, which proved it forever after not to be hypothetical.
An hypothesis, then, in the first stage of inquiry, far from being
inconsistent with sound philosophy, may be said to be essential to it.
But it is essential only in this first stage, as suggesting what is
afterwards to be verified or disproved; and, when the experiments or
observations to which it directs us do not verify it, it is no longer
to be entertained, even as an hypothesis. If we observe a phenomenon,
which we never have observed before, it is absolutely impossible for
us, not to think of the analogous cases which we may have seen; since
they are suggested by a principal of association, which is as truly
a part of our constitution, as the senses with which we perceived
the phenomenon itself; and, if any of these analogies strike us as
remarkably coincident, it is equally impossible for us not to imagine,
that the cause, which we knew in that former instance, may also be
present in this analogical instance, and that they _may_, therefore,
both be reduced to the same class. To stop here, and, from this mere
analogy, to infer positive identity of the causes, and to follow out
the possible consequences in innumerable applications, would be to do,
as many great artists in systematizing have done. What a philosopher,
of sounder views, however, would do in such a case, is very different.
He would assume, indeed, as _possible_ or perhaps as _probable_, the
existence of the supposed cause. But he would assume it, only to direct
his examination of its reality, by investigating, as far as he was
able, from past experience, what the circumstances would have been, in
every respect, if the cause supposed had been actually present; and,
even if these were all found to be exactly coincident, though he would
think the presence of the cause more probable, he would be very far
from considering it as certain, and would still endeavour to lessen the
chances of fallacy, by watching the circumstances, should they again
recur, and varying them, by experiment, in every possible way.
This patience and caution, however, essential as they are to just
philosophizing, require, it must be confessed, no slight efforts of
self-denial, but of a self-denial which is as necessary to intellectual
excellence as the various moral species of self-denial are to
excellence and virtue.
“Mr Locke, I think,” says Dr Reid, “mentions an eminent musician,
who believed that God created the world in six days, and rested the
seventh, because there are but seven notes in music. I myself,” he
continues, “knew one of that profession, who thought that there could
be only three parts in harmony, to wit, bass, tenor, and treble;
because there are but three persons in the Trinity.”[30]
The minds that could be satisfied with analogies so very slight, must,
indeed, have been little acquainted with the principles of philosophic
inquiry; and yet how many systems have been advanced in different ages,
admired by multitudes, who knew them only by name, and still more
revered by the philosophers, who gloried in adopting them, that have
been founded on analogies almost as slight.
“The philosophers who form hypothetical systems of the universe, and of
all its most secret laws,” says Voltaire, in one of his lively similes,
“are like our travellers that go to Constantinople, and think that they
must tell us a great deal about the seraglio. They pretend to know
every thing which passes within it--the whole secret history of the
Sultan and his favourites, and they have seen nothing but its outside
walls.”
In one respect, however, philosophers, in their hypothetical systems,
far outdo the travellers to Constantinople. They not merely tell us
secrets of nature, which they have no opportunity of learning, but they
believe the very tales of their own fancy. To see any usual phenomenon,
is, indeed, to wonder at it, at first; but to explain it, is almost the
very next step, reason serving rather to defend the explanation, when
it is made, than to assist greatly in making it; and, in many cases,
each philosopher has his separate explanation, on which he is disposed
to put as much reliance, as on the certainty of the fact itself,
not abandoning the hypothesis, even though the fact should prove to
have been different, but making it bend, with a happy pliability, to
all the diversities discovered, so as at last, perhaps, to account
for circumstances the very reverse of those which it was originally
invented to explain. “I have heard,” says Condillac, “of a philosopher,
who had the happiness of thinking that he had discovered a principle,
which was to explain all the wonderful phenomena of chemistry; and who,
in the ardour of his self-congratulation, hastened to communicate his
discovery to a skilful chemist. The chemist had the kindness to listen
to him, and then calmly told him, that there was but one unfortunate
circumstance for his discovery, which was, that the chemical _facts_
were exactly the reverse of what he had supposed. Well then, said the
philosopher, have the goodness to tell me _what_ they are, that I may
explain them by my system.”[31] To those who know that fondness for
conjecture, which may almost be said to be a sort of intellectual
appetite, there is nothing in all the wonders which Swift tells us of
his fabled Houynhnhms, that marks them more strongly as a different
race from mankind, than the total absence of hypothesis from their
systems of knowledge.
“I remember,” says Gulliver, “it was with extreme difficulty that I
could bring my master to understand the meaning of the word _opinion_,
or how a point could be disputable; because reason taught us to
affirm or deny only when we are certain; and beyond our knowledge we
cannot do either. So that controversies, wranglings, disputes, and
positiveness, in false or dubious propositions, are evils unknown among
the Houynhnhms. In the like manner, when I used to explain to him our
several systems of Natural Philosophy, he would laugh, that a creature
pretending to reason, should value itself upon the knowledge of other
people's conjectures, and in things, where that knowledge, if it were
certain, could be of no use. Wherein he agreed entirely with the
sentiments of Socrates, as Plato delivers them, which I mention as the
highest honour I can do that Prince of philosophers. I have often since
reflected what destruction such a doctrine would make in the libraries
of Europe, and how many paths to fame would be then shut up in the
learned world.”[32]
While I wish to caution you against a fondness for hypotheses, by
shewing you, not merely that they are liable to error,--for inquiry,
of every kind, must be so in some degree,--but that, in truth, they
leave the real difficulty of the succession of the observed consequents
to the observed antecedents as great as before, and only add, to the
supposed difficulty of explaining one sequence, the necessity of
explaining a sequence additional,--I must remark, at the same time,
that what is commonly termed _theory_, in opposition to _hypothesis_,
is far from being so different from it as is commonly represented,--at
least, in the very wide application which is usually made of it. We
are told, by those who lay down rules of philosophizing, that the
object of philosophy is, to observe particulars, and, from these, to
frame general laws, which may, again, be applied to the explanation of
particulars; and the view which is thus given of the real province of
philosophy is undoubtedly a just one;--but there is an ambiguity in the
language which may deceive you, and with respect to which, therefore,
it is necessary for you to be on your guard. If, by the term _general
law_, be meant the agreement in some common circumstances of a number
of events observed, there can be no question that we proceed safely in
framing it, and that what we have already found in a number of events,
must be applicable to that number of events; in the same manner, as,
after combining in the term _animal_ the circumstances in which a dog,
a horse, a sheep agree, we cannot err in applying the term animal to a
dog, a horse, a sheep. But the only particular to which, in this case,
we can, with perfect confidence, apply a general law, are the very
particulars that have been before observed by us. If it be understood
as more general than the circumstances observed, and, therefore,
capable of being applied with perfect certainty to the explanation of
new phenomena, we evidently, to the extent in which the general law is
applied beyond the circumstances observed, proceed on mere supposition,
as truly, as in any hypothesis which we could have framed; and though
the supposition may be more and more certain, in proportion to the
number of cases thus generalized, and the absence of any circumstance
which can be supposed, in the new case, to be inconsistent with it,
it never can amount to actual certainty. Let us take, for example,
one of the most striking cases of this sort. That bodies tend to each
other, _in all circumstances_, with a force increasing directly as
their quantities, and inversely as the squares of their distances, may
seem in the highest degree probable indeed, from the innumerable facts
observed on our globe, and in the magnificent extent of the planetary
movements; but it cannot be said to be certain at all distances, in
which we have never had an opportunity of making observations,--as
it seems to be verified in the heights of our atmosphere, and in the
distances of the planets, in their orbits, from the sun, and from
each other. It is not necessary, however, to refer, for possible
exceptions, to spaces that are beyond our observation; since, on the
surface of our own earth, there is abundant evidence, that the law
does _not_ hold _universally_. Every quiescent mass that is capable of
greater compression, and of which the particles, therefore, before that
compression, are not in absolute contact, shews sufficiently, that the
principle of attraction, which, of itself, would have brought them into
actual contact, must have ceased to operate, while there was still a
space between the particles that would have allowed its free operation;
and, in the phenomena of _elasticity_, and impulse in general, it has
not merely ceased, but is actually reversed,--the bodies which, at all
visible distances, exhibited a reciprocal _attraction_, now exhibiting
a reciprocal _repulsion_, in consequence of which they mutually fly
off, as readily as they before approached,--that is to say, the
tendency of bodies to each other being converted into a tendency _from_
each other, by a mere change of distance, so slight as to be almost
inappreciable. When a ball rebounds from the earth, toward which it
moved rapidly before, and the gravitating tendency is thus evidently
reversed, without the intervention of any foreign force, what eye,
though it be aided by all the nicest apparatus of optical art, can
discover the lines which separate those infinitesimal differences
of proximity, at which the particles of the ball still continue to
gravitate toward the earth, and are afterwards driven from it in an
opposite direction;--yet the phenomenon itself is a sufficient proof,
that in these spaces, which seem, to our organs of sense, so completely
the same, that it is absolutely impossible for us to distinguish them,
the reciprocal tendencies of the particles of the ball and of the earth
are as truly opposite, as if the laws of gravitation had, at the moment
at which the rebound begins, been reversed through the whole system of
the universe.
It is, indeed, scarcely possible to imagine a more striking proof of
the danger of extending, with too great certainty, a general law, than
this instant conversion of _attraction_ into _repulsion_, without
the addition of any new bodies, without any change in the nature of
the bodies themselves, and a change of their circumstances so very
slight, as to be absolutely indistinguishable, but for the opposite
motions that result from it, with a change of their circumstances.
After observing the gravity of bodies, at all heights of our
atmosphere, and extending our survey through the wide spaces of our
solar system,--computing the tendency of the planets to the sun, and
their disturbing forces, as they operate on each other,--and finding
the resulting motions exactly to correspond with those which we had
predicted by theory;--in these circumstances, after an examination
so extensive, if we had affirmed, as an universal law of matter,
that, at all distances, bodies tend toward each other, we should
have considered the wideness of the induction, as justifying the
affirmation; and yet, even in this case, we find, on the surface of
our earth, in the mutual shocks of bodies, and in their very rest,
sufficient evidence, that, in making the universal affirmation, we
should have reasoned falsely. There is no theory, then, which, if
applied to the explanation of _new_ phenomena, is not, to a certain
degree, conjectural; because it must proceed on the supposition, that
what was true in certain circumstances, is true also in circumstances
that have not been observed. It admits of certainty, only when it is
applied to the very substances observed,--in the very circumstances
observed,--in which case, it may be strictly said to be nothing more
than the application of a general term to the particulars, which we
have before agreed to comprehend in it. Whatever is more than this is
truly hypothetical,--the difference being, that we commonly give the
name of _hypothesis_ to cases, in which we suppose the intervention
of some substance, of the existence of which, as present in the
phenomenon, we have no direct proof, or of some additional quality of a
substance before unobserved,--and the name of _theory_ to cases, which
do not suppose the existence of any substance, that is not actually
observed, or of any quality that has not been actually observed, but
merely the continuance, in certain _new_ circumstances, of tendencies
observed in other circumstances. Thus, if a planet were discovered
revolving in the space which separates the orbits of any two planets
at present known, were we to suppose of matter, in this new situation,
that it would be subject to the same exact law of gravitation, to which
the other planets were known to be subject, and to predict its place in
the heavens, at any time, according to this law, we should be said to
form a theory of its motions; as we should not take for granted, any
new quality of a substance, or the existence of any substance, which
was not evidently present, but only of _tendencies_ observed before in
other circumstances,--analogous indeed, but not absolutely the same.
We should be said to form an hypothesis on the subject, if, making
the same prediction, as to its motions, and place in the heavens, at
any given time, we were to ascribe the centripetal tendency, which
confines it within its orbit, to the impulse of ether, or to any other
mechanical cause. The terms, however, I must confess, though the
distinction which I have now stated would be, in all cases, a very
convenient one, are used very loosely, not in conversation merely, but
in the writings of philosophers,--an hypothesis often meaning nothing
more than a theory, to which we have not given our assent,--and a
theory, an hypothesis which we have adopted, or still more, one which
we have formed ourselves.
A _theory_, then, even in that best sense, to which I wish it
accurately confined, as often as it ventures a single hair-breadth
beyond the line of former observation, may be wrong, as an hypothesis
may be wrong. But, in a theory, in this sense of it, there are both
less risk of error, and less extensive evil from error, than in an
hypothesis. There is less risk of error, because we speak only of the
properties of bodies, that must be allowed actually to exist; and the
evil of error is, for the same reason, less extensive, since it must be
confined to this single point; whereas, if we were to imagine falsely
the presence of some third substance, our supposition might involve as
many errors, as that substance has qualities; since we should be led
to suppose, and expect, some or all of the other consequences, which
usually attend it, when really present.
The practical conclusion to be drawn from all this very long
discussion, is, that we should use hypotheses to suggest and direct
inquiry, not to terminate or supersede it; and that, in theorizing,--as
the chance of error, in the application of a general law, diminishes,
in proportion to the number of analogous cases, in which it is observed
to hold,--we should not form any general proposition, till after as
wide an induction, as it is possible for us to make; and, in the
subsequent application of it to particulars, should never content
ourselves, in any new circumstances, with the mere probability, however
high, which this application of it affords; while it is possible for us
to verify, or disprove it, by actual experiment.
FOOTNOTES:
[30] On the Powers of the Human Mind, Essay vi. Chap. viii. Vol. II. p.
334. 8vo. _edit._
[31] Traite des Systemes, chap. xii. Vol. II. p. 372.
[32] Travels, Part iv, chap. 8. Swift's Works, _edit._ Nichols, Vol.
ix. p. 300.
LECTURE IX.
RECAPITULATION OF THE FOUR PRECEDING LECTURES; AND APPLICATION OF THE
LAWS OF PHYSICAL INQUIRY TO THE STUDY OF MIND, COMMENCED.
For several Lectures, Gentlemen, we have been employed in considering
the objects that are to be had in view, in Physical Inquiry in general,
a clear conception of which seems to me as essential to the Philosophy
of Mind, as to the Philosophy of Matter. I should now proceed to apply
these general remarks more particularly to our own science; but, before
doing this, it may be of advantage to retrace slightly our steps in the
progress already made.
All inquiry, with respect to the various substances in nature, we have
seen, must regard them as they exist in _space_, or as they exist in
_time_,--the inquiry, in the one case, being into their composition;
the inquiry, in the other case, into the changes which they exhibit.
The first of these views we found to be very simple, having, for
its object, only the discovery of what is actually before us at the
moment,--which, therefore, if we had been endowed with senses of
greater delicacy and acuteness, we might have known, without any
inquiry whatever. It is the investigation of the elements, or separate
bodies, that exist together, in the substances which we considered, or
rather that constitute the substances which we considered, by occupying
the space which we assign to the one imaginary aggregate, and are
regarded by us as one substance,--not from any absolute unity which
they have in nature, since the elementary atoms, however continuous or
near, have an existence as truly separate and independent, as if they
had been created at the distance of worlds,--but from a unity, that is
relative only to our incapacity of distinguishing them as separate. It
is to the imperfection of our senses, then, that this first division of
Physical Inquiry owes its origin; and its most complete results could
enable us to discover only, what has been before our eyes from the
moment of our birth.
The second division of inquiry,--that which relates to the successions
of phenomena in time,--we found, however, to have a different origin;
since the utmost perfection of our mere senses could show us only what
_is_, at the moment of perception, not what _has been_, nor what _will
be_; and there is nothing in any qualities of bodies perceived by us,
which, without experience, could enable us to predict the changes that
are to occur in them. The foundation of all inquiry, with respect to
phenomena as successive, we found to be that most important law, or
original tendency, of our nature, in consequence of which we not merely
perceive the changes exhibited to us at one particular moment, but
from this perception, are led irresistibly to believe, that similar
changes _have_ constantly taken place, in all similar circumstances,
and _will_ constantly take place, as often as the future circumstances
shall be exactly similar to the present. We hence consider events, not
as casually antecedent and consequent, but as invariably antecedent
and consequent,--or, in other words, as causes and effects; and we
give the name of _power_ to this permanent relation of the invariable
antecedent to its invariable consequent. The powers of substances,
then, concerning which so many vague, and confused, and mysterious
notions prevail, are only another name for the substances themselves,
in relation to other substances,--not any thing separate from them
and intermediate,--as the _form_ of a body, concerning which too,
for many ages, notions as vague and mysterious prevailed, is not any
thing different from the body, but is only the body itself, considered
according to the relative position of its elements. Form is the
relation of immediate proximity, which bodies bear to each other in
_space_;--power is the relation of immediate and uniform proximity,
which events bear to each other in _time_; and the relation, far from
being different, as is commonly supposed, when applied to matter and to
spirit, is precisely the same in kind, whether the events, of which we
think, be material or immaterial. It is of invariable antecedence that
we speak alike in both cases, and of invariable antecedence only. When
we say, that a magnet has the power of attracting iron, we mean only,
that a magnet cannot be brought near iron, without the instant motion
of the iron towards it. When we say, in treating of _mental_ influence,
that man, in the ordinary circumstances of health, and when free from
any foreign restraint, has the power of moving his hand, we mean only,
that, in these circumstances, he cannot will to move his hand, without
its consequent motion. When we speak of the omnipotence of the Supreme
of Beings,--who is the fountain of all power, as he is the fountain of
all existence,--we mean only, that the universe arose at his command,
as its instant consequence, and that whatever he _wills_ to exist or
perish, exists, or is no more.