OF THE EVIDENCE OF THE LAW OF UNIVERSAL CAUSATION.
§ 1. We have now completed our review of the logical processes by which
the laws, or uniformities, of the sequence of phenomena, and those
uniformities in their coexistence which depend on the laws of their
sequence, are ascertained or tested. As we recognised in the
commencement, and have been enabled to see more clearly in the progress
of the investigation, the basis of all these logical operations is the
law of causation. The validity of all the Inductive Methods depends on
the assumption that every event, or the beginning of every phenomenon,
must have some cause; some antecedent, on the existence of which it is
invariably and unconditionally consequent. In the Method of Agreement
this is obvious; that method avowedly proceeding on the supposition that
we have found the true cause as soon as we have negatived every other.
The assertion is equally true of the Method of Difference. That method
authorizes us to infer a general law from two instances; one, in which A
exists together with a multitude of other circumstances, and B follows;
another, in which, A being removed, and all other circumstances
remaining the same, B is prevented. What, however, does this prove? It
proves that B, in the particular instance, cannot have had any other
cause than A; but to conclude from this that A was the cause, or that A
will on other occasions be followed by B, is only allowable on the
assumption that B must have some cause; that among its antecedents in
any single instance in which it occurs, there must be one which has the
capacity of producing it at other times. This being admitted, it is seen
that in the case in question that antecedent can be no other than A;
but, that if it be no other than A it must be A, is not proved, by these
instances at least, but taken for granted. There is no need to spend
time in proving that the same thing is true of the other Inductive
Methods. The universality of the law of causation is assumed in them
all.
But is this assumption warranted? Doubtless (it may be said) _most_
phenomena are connected as effects with some antecedent or cause, that
is, are never produced unless some assignable fact has preceded them;
but the very circumstance that complicated processes of induction are
sometimes necessary, shows that cases exist in which this regular order
of succession is not apparent to our unaided apprehension. If, then, the
processes which bring these cases within the same category with the
rest, require that we should assume the universality of the very law
which they do not at first sight appear to exemplify, is not this a
_petitio principii_? Can we prove a proposition, by an argument which
takes it for granted? And if not so proved, on what evidence does it
rest?
For this difficulty, which I have purposely stated in the strongest
terms it will admit of, the school of metaphysicians who have long
predominated in this country find a ready salvo. They affirm, that the
universality of causation is a truth which we cannot help believing;
that the belief in it is an instinct, one of the laws of our believing
faculty. As the proof of this, they say, and they have nothing else to
say, that everybody does believe it; and they number it among the
propositions, rather numerous in their catalogue, which may be logically
argued against, and perhaps cannot be logically proved, but which are of
higher authority than logic, and so essentially inherent in the human
mind, that even he who denies them in speculation, shows by his habitual
practice that his arguments make no impression upon himself.
Into the merits of this question, considered as one of psychology, it
would be foreign to my purpose to enter here: but I must protest against
adducing, as evidence of the truth of a fact in external nature, the
disposition, however strong or however general, of the human mind to
believe it. Belief is not proof, and does not dispense with the
necessity of proof. I am aware, that to ask for evidence of a
proposition which we are supposed to believe instinctively, is to expose
oneself to the charge of rejecting the authority of the human faculties;
which of course no one can consistently do, since the human faculties
are all which any one has to judge by: and inasmuch as the meaning of
the word evidence is supposed to be, something which when laid before
the mind, induces it to believe; to demand evidence when the belief is
ensured by the mind's own laws, is supposed to be appealing to the
intellect against the intellect. But this, I apprehend, is a
misunderstanding of the nature of evidence. By evidence is not meant
anything and everything which produces belief. There are many things
which generate belief besides evidence. A mere strong association of
ideas often causes a belief so intense as to be unshakeable by
experience or argument. Evidence is not that which the mind does or must
yield to, but that which it ought to yield to, namely, that, by yielding
to which, its belief is kept conformable to fact. There is no appeal
from the human faculties generally, but there is an appeal from one
human faculty to another; from the judging faculty, to those which take
cognizance of fact, the faculties of sense and consciousness. The
legitimacy of this appeal is admitted whenever it is allowed that our
judgments ought to be conformable to fact. To say that belief suffices
for its own justification is making opinion the test of opinion; it is
denying the existence of any outward standard, the conformity of an
opinion to which constitutes its truth. We call one mode of forming
opinions right and another wrong, because the one does, and the other
does not, tend to make the opinion agree with the fact--to make people
believe what really is, and expect what really will be. Now a mere
disposition to believe, even if supposed instinctive, is no guarantee
for the truth of the thing believed. If, indeed, the belief ever
amounted to an irresistible necessity, there would then be no _use_ in
appealing from it, because there would be no possibility of altering it.
But even then the truth of the belief would not follow; it would only
follow that mankind were under a permanent necessity of believing what
might possibly not be true; in other words, that a case might occur in
which our senses or consciousness, if they could be appealed to, might
testify one thing, and our reason believe another. But in fact there is
no such permanent necessity. There is no proposition of which it can be
asserted that every human mind must eternally and irrevocably believe
it. Many of the propositions of which this is most confidently stated,
great numbers of human beings have disbelieved. The things which it has
been supposed that nobody could possibly help believing, are
innumerable; but no two generations would make out the same catalogue of
them. One age or nation believes implicitly what to another seems
incredible and inconceivable; one individual has not a vestige of a
belief which another deems to be absolutely inherent in humanity. There
is not one of these supposed instinctive beliefs which is really
inevitable. It is in the power of every one to cultivate habits of
thought which make him independent of them. The habit of philosophical
analysis, (of which it is the surest effect to enable the mind to
command, instead of being commanded by, the laws of the merely passive
part of its own nature,) by showing to us that things are not
necessarily connected in fact because their ideas are connected in our
minds, is able to loosen innumerable associations which reign
despotically over the undisciplined or early-prejudiced mind. And this
habit is not without power even over those associations which the school
of which I have been speaking regard as connate and instinctive. I am
convinced that any one accustomed to abstraction and analysis, who will
fairly exert his faculties for the purpose, will, when his imagination
has once learnt to entertain the notion, find no difficulty in
conceiving that in some one for instance of the many firmaments into
which sidereal astronomy now divides the universe, events may succeed
one another at random, without any fixed law; nor can anything in our
experience, or in our mental nature, constitute a sufficient, or indeed
any, reason for believing that this is nowhere the case.
Were we to suppose (what it is perfectly possible to imagine) that the
present order of the universe were brought to an end, and that a chaos
succeeded in which there was no fixed succession of events, and the past
gave no assurance of the future; if a human being were miraculously kept
alive to witness this change, he surely would soon cease to believe in
any uniformity, the uniformity itself no longer existing. If this be
admitted, the belief in uniformity either is not an instinct, or it is
an instinct conquerable, like all other instincts, by acquired
knowledge.
But there is no need to speculate on what might be, when we have
positive and certain knowledge of what has been. It is not true as a
matter of fact, that mankind have always believed that all the
successions of events were uniform and according to fixed laws. The
Greek philosophers, not even excepting Aristotle, recognised Chance and
Spontaneity ([Greek: tychê] and [Greek: to automaton]) as among the
agents in nature; in other words, they believed that to that extent
there was no guarantee that the past had been similar to itself, or that
the future would resemble the past. Even now a full half of the
philosophical world, including the very same metaphysicians who contend
most for the instinctive character of the belief in uniformity, consider
one important class of phenomena, volitions, to be an exception to the
uniformity, and not governed by a fixed law.[26]
§ 2. As was observed in a former place,[27] the belief we entertain in
the universality, throughout nature, of the law of cause and effect, is
itself an instance of induction; and by no means one of the earliest
which any of us, or which mankind in general, can have made. We arrive
at this universal law, by generalization from many laws of inferior
generality. We should never have had the notion of causation (in the
philosophical meaning of the term) as a condition of all phenomena,
unless many cases of causation, or in other words, many partial
uniformities of sequence, had previously become familiar. The more
obvious of the particular uniformities suggest, and give evidence of,
the general uniformity, and the general uniformity, once established,
enables us to prove the remainder of the particular uniformities of
which it is made up. As, however, all rigorous processes of induction
presuppose the general uniformity, our knowledge of the particular
uniformities from which it was first inferred was not, of course,
derived from rigorous induction, but from the loose and uncertain mode
of induction _per enumerationem simplicem_: and the law of universal
causation, being collected from results so obtained, cannot itself rest
on any better foundation.
It would seem, therefore, that induction _per enumerationem simplicem_
not only is not necessarily an illicit logical process, but is in
reality the only kind of induction possible; since the more elaborate
process depends for its validity on a law, itself obtained in that
inartificial mode. Is there not then an inconsistency in contrasting the
looseness of one method with the rigidity of another, when that other is
indebted to the looser method for its own foundation?
The inconsistency, however, is only apparent. Assuredly, if induction by
simple enumeration were an invalid process, no process grounded on it
could be valid; just as no reliance could be placed on telescopes, if we
could not trust our eyes. But though a valid process, it is a fallible
one, and fallible in very different degrees: if therefore we can
substitute for the more fallible forms of the process, an operation
grounded on the same process in a less fallible form, we shall have
effected a very material improvement. And this is what scientific
induction does.
A mode of concluding from experience must be pronounced untrustworthy,
when subsequent experience refuses to confirm it. According to this
criterion, induction by simple enumeration--in other words,
generalization of an observed fact from the mere absence of any known
instance to the contrary--affords in general a precarious and unsafe
ground of assurance; for such generalizations are incessantly
discovered, on further experience, to be false. Still, however, it
affords some assurance, sufficient, in many cases, for the ordinary
guidance of conduct. It would be absurd to say, that the generalizations
arrived at by mankind in the outset of their experience, such as these,
Food nourishes, Fire burns, Water drowns, were unworthy of reliance.[28]
There is a scale of trustworthiness in the results of the original
unscientific Induction; and on this diversity (as observed in the fourth
chapter of the present book) depend the rules for the improvement of the
process. The improvement consists in correcting one of these
inartificial generalizations by means of another. As has been already
pointed out, this is all that art can do. To test a generalization, by
showing that it either follows from, or conflicts with, some stronger
induction, some generalization resting on a broader foundation of
experience, is the beginning and end of the logic of Induction.
§ 3. Now the precariousness of the method of simple enumeration is in an
inverse ratio to the largeness of the generalization. The process is
delusive and insufficient, exactly in proportion as the subject-matter
of the observation is special and limited in extent. As the sphere
widens, this unscientific method becomes less and less liable to
mislead; and the most universal class of truths, the law of causation
for instance, and the principles of number and of geometry, are duly and
satisfactorily proved by that method alone, nor are they susceptible of
any other proof.
With respect to the whole class of generalizations of which we have
recently treated, the uniformities which depend on causation, the truth
of the remark just made follows by obvious inference from the principles
laid down in the preceding chapters. When a fact has been observed a
certain number of times to be true, and is not in any instance known to
be false; if we at once affirm that fact as an universal truth or law of
nature, without testing it by any of the four methods of induction, nor
deducing it from other known laws, we shall in general err grossly: but
we are perfectly justified in affirming it as an empirical law, true
within certain limits of time, place, and circumstance, provided the
number of coincidences be greater than can with any probability be
ascribed to chance. The reason for not extending it beyond those limits
is, that the fact of its holding true within them may be a consequence
of collocations, which cannot be concluded to exist in one place because
they exist in another; or may be dependent on the accidental absence of
counteracting agencies, which any variation of time, or the smallest
change of circumstances, may possibly bring into play. If we suppose,
then, the subject-matter of any generalization to be so widely diffused
that there is no time, no place, and no combination of circumstances,
but must afford an example either of its truth or of its falsity, and if
it be never found otherwise than true, its truth cannot depend on any
collocations, unless such as exist at all times and places; nor can it
be frustrated by any counteracting agencies, unless by such as never
actually occur. It is, therefore, an empirical law coextensive with all
human experience; at which point the distinction between empirical laws
and laws of nature vanishes, and the proposition takes its place among
the most firmly established as well as largest truths accessible to
science.
Now, the most extensive in its subject-matter of all generalizations
which experience warrants, respecting the sequences and coexistences of
phenomena, is the law of causation. It stands at the head of all
observed uniformities, in point of universality, and therefore (if the
preceding observations are correct) in point of certainty. And if we
consider, not what mankind would have been justified in believing in the
infancy of their knowledge, but what may rationally be believed in its
present more advanced state, we shall find ourselves warranted in
considering this fundamental law, though itself obtained by induction
from particular laws of causation, as not less certain, but on the
contrary, more so, than any of those from which it was drawn. It adds
to them as much proof as it receives from them. For there is probably no
one even of the best established laws of causation which is not
sometimes counteracted, and to which, therefore, apparent exceptions do
not present themselves, which would have necessarily and justly shaken
the confidence of mankind in the universality of those laws, if
inductive processes founded on the universal law had not enabled us to
refer those exceptions to the agency of counteracting causes, and
thereby reconcile them with the law with which they apparently conflict.
Errors, moreover, may have slipped into the statement of any one of the
special laws, through inattention to some material circumstance: and
instead of the true proposition, another may have been enunciated, false
as an universal law, though leading, in all cases hitherto observed, to
the same result. To the law of causation, on the contrary, we not only
do not know of any exception, but the exceptions which limit or
apparently invalidate the special laws, are so far from contradicting
the universal one, that they confirm it; since in all cases which are
sufficiently open to our observation, we are able to trace the
difference of result, either to the absence of a cause which had been
present in ordinary cases, or to the presence of one which had been
absent.
The law of cause and effect, being thus certain, is capable of imparting
its certainty to all other inductive propositions which can be deduced
from it; and the narrower inductions may be regarded as receiving their
ultimate sanction from that law, since there is no one of them which is
not rendered more certain than it was before, when we are able to
connect it with that larger induction, and to show that it cannot be
denied, consistently with the law that everything which begins to exist
has a cause. And hence we are justified in the seeming inconsistency, of
holding induction by simple enumeration to be good for proving this
general truth, the foundation of scientific induction, and yet refusing
to rely on it for any of the narrower inductions. I fully admit that if
the law of causation were unknown, generalization in the more obvious
cases of uniformity in phenomena would nevertheless be possible, and
though in all cases more or less precarious, and in some extremely so,
would suffice to constitute a certain measure of probability: but what
the amount of this probability might be, we are dispensed from
estimating, since it never could amount to the degree of assurance which
the proposition acquires, when, by the application to it of the Four
Methods, the supposition of its falsity is shown to be inconsistent with
the Law of Causation. We are therefore logically entitled, and, by the
necessities of scientific Induction, required, to disregard the
probabilities derived from the early rude method of generalizing, and to
consider no minor generalization as proved except so far as the law of
causation confirms it, nor probable except so far as it may reasonably
be expected to be so confirmed.
§ 4. The assertion, that our inductive processes assume the law of
causation, while the law of causation is itself a case of induction, is
a paradox, only on the old theory of reasoning, which supposes the
universal truth, or major premise, in a ratiocination, to be the real
proof of the particular truths which are ostensibly inferred from it.
According to the doctrine maintained in the present treatise,[29] the
major premise is not the proof of the conclusion, but is itself proved,
along with the conclusion from the same evidence. "All men are mortal"
is not the proof that Lord Palmerston is mortal; but our past experience
of mortality authorizes us to infer _both_ the general truth and the
particular fact, and the one with exactly the same degree of assurance
as the other. The mortality of Lord Palmerston is not an inference from
the mortality of all men, but from the experience which proves the
mortality of all men; and is a correct inference from experience, if
that general truth is so too. This relation between our general beliefs
and their particular applications holds equally true in the more
comprehensive case which we are now discussing. Any new fact of
causation inferred by induction, is rightly inferred, if no other
objection can be made to the inference than can be made to the general
truth that every event has a cause. The utmost certainty which can be
given to a conclusion arrived at in the way of inference, stops at this
point. When we have ascertained that the particular conclusion must
stand or fall with the general uniformity of the laws of nature--that it
is liable to no doubt except the doubt whether every event has a
cause--we have done all that can be done for it. The strongest assurance
we can obtain of any theory respecting the cause of a given phenomenon,
is that the phenomenon has either that cause or none.
The latter supposition might have been an admissible one in a very early
period of our study of nature. But we have been able to perceive that in
the stage which mankind have now reached, the generalization which gives
the Law of Universal Causation has grown into a stronger and better
induction, one deserving of greater reliance, than any of the
subordinate generalizations. We may even, I think, go a step further
than this, and regard the certainty of that great induction as not
merely comparative, but, for all practical purposes, absolute.
The considerations which, as I apprehend, give, at the present day, to
the proof of the law of uniformity of succession as true of all
phenomena without exception, this character of completeness and
conclusiveness, are the following:--First, that we now know it directly
to be true of far the greatest number of phenomena; that there are none
of which we know it not to be true, the utmost that can be said being,
that of some we cannot positively from direct evidence affirm its truth;
while phenomenon after phenomenon, as they become better known to us,
are constantly passing from the latter class into the former; and in all
cases in which that transition has not yet taken place, the absence of
direct proof is accounted for by the rarity or the obscurity of the
phenomena, our deficient means of observing them, or the logical
difficulties arising from the complication of the circumstances in which
they occur; insomuch that, notwithstanding as rigid a dependence on
given conditions as exists in the case of any other phenomenon, it was
not likely that we should be better acquainted with those conditions
than we are. Besides this first class of considerations, there is a
second, which still further corroborates the conclusion. Although there
are phenomena the production and changes of which elude all our attempts
to reduce them universally to any ascertained law; yet in every such
case, the phenomenon, or the objects concerned in it, are found in some
instances to obey the known laws of nature. The wind, for example, is
the type of uncertainty and caprice, yet we find it in some cases
obeying with as much constancy as any phenomenon in nature the law of
the tendency of fluids to distribute themselves so as to equalize the
pressure on every side of each of their particles; as in the case of the
trade winds, and the monsoons. Lightning might once have been supposed
to obey no laws; but since it has been ascertained to be identical with
electricity, we know that the very same phenomenon in some of its
manifestations is implicitly obedient to the action of fixed causes. I
do not believe that there is now one object or event in all our
experience of nature, within the bounds of the solar system at least,
which has not either been ascertained by direct observation to follow
laws of its own, or been proved to be closely similar to objects and
events which, in more familiar manifestations, or on a more limited
scale, follow strict laws: our inability to trace the same laws on a
larger scale and in the more recondite instances, being accounted for by
the number and complication of the modifying causes, or by their
inaccessibility to observation.
The progress of experience, therefore, has dissipated the doubt which
must have rested on the universality of the law of causation while there
were phenomena which seemed to be _sui generis_, not subject to the same
laws with any other class of phenomena, and not as yet ascertained to
have peculiar laws of their own. This great generalization, however,
might reasonably have been, as it in fact was, acted on as a probability
of the highest order, before there were sufficient grounds for receiving
it as a certainty. For, whatever has been found true in innumerable
instances, and never found to be false after due examination in any, we
are safe in acting on as universal provisionally, until an undoubted
exception appears; provided the nature of the case be such that a real
exception could scarcely have escaped our notice. When every phenomenon
that we ever knew sufficiently well to be able to answer the question,
had a cause on which it was invariably consequent, it was more rational
to suppose that our inability to assign the causes of other phenomena
arose from our ignorance, than that there were phenomena which were
uncaused, and which happened to be exactly those which we had hitherto
had no sufficient opportunity of studying.
It must, at the same time, be remarked, that the reasons for this
reliance do not hold in circumstances unknown to us, and beyond the
possible range of our experience. In distant parts of the stellar
regions, where the phenomena may be entirely unlike those with which we
are acquainted, it would be folly to affirm confidently that this
general law prevails, any more than those special ones which we have
found to hold universally on our own planet. The uniformity in the
succession of events, otherwise called the law of causation, must be
received not as a law of the universe, but of that portion of it only
which is within the range of our means of sure observation, with a
reasonable degree of extension to adjacent cases. To extend it further
is to make a supposition without evidence, and to which, in the absence
of any ground from experience for estimating its degree of probability,
it would be idle to attempt to assign any.[30]