Thomas Reid.

The works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters online

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duet, are the foundation of all political rea-
soning, and of common prudence in the con-
duct of life. Hardly can a man form any
project in public or in private life, which
does not depend upon the conduct of other
men, as well as his own, and which does not
go upon the supposition that men will act
such a part in such circumstances. This
evidence may be probable in a very high
degree ; but can never be demonstrative.
The best concerted project may fail, and
wise counsels may be frustrated, because
some individual acted a part which it would
have been against all reason to expect.

Another kind of probable evidence, the
counterpart of the last, is that by which we
collect men's characters and designs from
their actions, speech, and other external

We see not men's hearts, nor the prin-
ciples by which they are actuated ; but
there are external signs of their principles
and dispositions, which, though not certain,
may sometimes be more trusted than their
professions ; and it is from external signs
that we must draw all the knowledge we
can attain of men's characters.

The next kind of probable evidence I
mention, is that which mathematicians call
the probability of chances.

We attribute some events to chance, be
cause we know only the remote cause which
must produce some one event of a num-
ber ; but know not the more immediate
cause which determines a particular event
of that number in preference to the others.

I think all the chances about which we rea-
son in mathematics are of this kind. Thus,
in throwing a just die upon a table, we say
it is an equal chance which of the six sides
shall be turned up ; because neither the
person who throws, nor the bystanders,
know the precise measure of force and di-
rection necessary to turn up any one side
rather than another. There are here, there-
fore six events, one of which must happen ;
and as all are supposed to have equal pro-
bability, the probability of any one side
being turned up, the ace, for instance, is as
one to the remaining number, five.

The probability of turning up two ace*
2 12



[kssav VII.

with two dice is as one to thirty-five ; because
here there are thirty-six events, each of
which has equal probability.

Upon such principles as these, the doc-
trine of chances has furnished a field of de-
monstrative reasoning of great extent, al-
though the events about which this reason-
ing is employed be not necesssary, but con-
tingent, and be not certain, but probable.

This may seem to contradict a principle
before advanced, that contingent truths are
not capable of demonstration ; but it does
not : for, in the mathematical reasonings
about chance, the conclusion demonstrated,
is not, that such an event shall happen, but
that the probability of its happening bears
such a ratio to the probability of its failing ;
and this conclusion is necessary upon the
suppositions on which it is grounded.

The last kind of probable evidence I shall
mention, is that by which the known laws
of Nature have been discovered, and the
effects which have been produced by them
in former ages, or which may be expected
in time to come.

The laws of Nature are the rules by which
the Supreme Being governs the world. We
deduce them only from facts that fall within
our own observation, or are properly attested
by those who have observed them. [696]

The knowledge of some of the laws of
nature is necessary to all men in the con-
duct of life. These are soon discovered
even by savages. They know that fire
burns, that water drowns, that bodies gra-
vitate towards the earth. They know that
day and night, summer and winter, regu-
larly succeed each other. As far back as
their experience and information reach,
they know that these have happened regu-
larly ; and, upon this ground, they are led,
by the constitution of human nature, to ex-
pect that they will happen in time to come,
in like circumstances.

The knowledge which the philosopher
attains of the laws of Nature differs from
that of the vulgar, not in the first principles
on which it is grounded, but in its extent
and accuracy. He collects with care the
phsenomena that lead to the same conclu-
sion, and compares them with those that
seem to contradict or to limit it. He ob-
serves the circumstances on which every
pheenomenon depends, and distinguishes
them carefully from those that are accident-
ally conjoined with it. He puts natural
bodies in various situations, and applies
them to one another in various ways, on
purpose to observe the effect ; and thus ac-
quires from his senses a more extensive
knowledge of the course of Nature in a short
time, than could be collected by casual ob-
servation in many ages.

But what is the result of his laborious
researches ? It is, that, as far as he has

been able to observe, such things have
always happened in such circumstances, and
such bodies have always been found to have
such properties. These are matters of fact,
attested by sense, memory, and testimony,
just as the few facts which the vulgar know
are attested to them.

And what conclusions does the philoso-
pher draw from the facts he has collected ?
They are, that like events have happened
in former times in like circumstances, and
will happen in time to come ; and these con-
clusions are built on the very same ground
on which the simple rustic concludes that
the sun will rise to-morrow. [697]

Facts reduced to general rules, and the
consequences of those general rules, are all
that we really know of the material world.
And the evidence that such general rules
have no exceptions, as well as the evidence
that they will be the same in time to come
as they have been in time past, can never
be demonstrative. It is only that species
of evidence which philosophers call probable.
General rules may have exceptions or limit-
ations which no man ever had occasion to
observe. The laws of nature may be changed
by him who established them. But we are
led by our constitution to rely upon their
continuance with as little doubt as if it was.

I pretend not to have made a complete
enumeration of all the kinds of probable
evidence ; but those I have mentioned are
sufficient to shew, that the far greatest part,
and the most interesting part of our know-
ledge, must rest upon evidence of this kind ;
and that many things are certain for which
we have only that kind of evidence which
philosophers call probable.


of mr hume's scepticism with regard to


In the " Treatise of Human Nature,"
book I. part iv. § 1, the author undertakes
to prove two points : — First, That all that
is called human knowledge (meaning de-
monstrative knowledge) is only probability ;
and, seoowui,, That this probability, when
duly examined, evanishes by degrees, and
leaves at last no evidence at all : so that,
in the issue, there is no ground to believe
anyone proposition rather than its contrary;
and " all those are certainly fools who reason
or believe anything." [698]

According to this account, reason, that
boasted prerogative of man, and the light of
his mind, is an ignis faluus, which misleads
the wandering traveller, and leaves him at
last in absolute darkness.

How 'unhappy is the condition of man ;



bom under a necessity of believing contra-
dictions, -and of trusting to a guide who con-
fesses herself to be a false one !

It is some comfort, that this doctrine can
never be seriously adopted by any man in
his senses. And after this author had
shewn that " all the rules of logic require a
total extinction of all belief and evidence,"
he himself, and all men that are not insane,
must have believed many things, and yielded
assent to the evidence which he had ex-

This, indeed, he is so candid as to acknow-
ledge. " He finds himself absolutely and
necessarily determined, to live and talk and
act like other people in the common affairs
of life. And since reason is incapable of
dispelling these clouds, most fortunately it
happens, that nature herself suffices to that
purpose, and cures him of this philosophical
melancholy and delirium." See § 7.

This was surely a very kind and friendly
interposition of nature ; for the* effects of
this philosophical delirium, if carried into
life, must have been very melancholy.

But what pity is it, that nature, (what-
ever is meant by that personage,) so kind
in curing this delirium, should be so cruel
as to cause it. Doth the same fountain
' send forth sweet waters and bitter ? Is it
not more probable, that, if the cure was the
work of nature, the disease came from
another hand, and was the work of the
philosopher ? [699]

To pretend to prove by reasoning that
there is no force in reason, does indeed look
like a philosophical delirium. It is like a
man's pretending to see clearly, that he
himself and all other men are blind.

A common symptom of delirium is, to
- think that all, other men are fools or mad.
This appears to have been the case of our
author, who concluded, " That all those are
certainly fools who reason or believe any-

Whatever was the cause of this delirium,
it must be granted that, if it was real and
not feigned, it was not to be cured by rea-
soning ; for what can be more absurd than
to attempt to convince a man by reasoning
who disowns the authority of reason. It
was, therefore, very fortunate that Nature
found other means of curing it.

It may, however, not be improper to
inquire, whether, as the author thinks, it
was produced by a just application of the
rules of logic, or, as others may be apt to
think, by the misapplication and abuse of

First, Because we are fallible, the author
infers that all knowledge degenerates into

That man, and probably every created
being, is fallible ; and that a fallible being
cannot have that perfect comprehension

and assurance of truth which an infallible
being has — I think ought to be granted. It
becomes a fallible being to be modest, open
to new .light, and sensible that, by some
false bias, or by rash judging, he may be
misled. If this be called a degree of scep-
ticism, I cannot help approving of it, being
persuaded that the man who makes the best
use he can of the faculties which God has
given him, without thinking them more per-
fect than they really are, may have all the
belief that is necessary in the conduct of
life, and all that is necessary to his accept-
ance with his Maker. [700]

It is granted, then, that human judg-
ments ought always to be formed with an
humble sense of our fallibility in judging.

This is all that can be inferred by the
rules of logic from our being fallible. And
if this be all that is meant by our know-
ledge degenerating into probability, I know
no person of a different opinion.

But it may be observed, that the author
here uses the word probability in a sense
for which I know no authority but his own.
Philosophers understand probability as op-
posed to demonstration ; the vulgar as
opposed to certainty ; but this author un-
derstands it as opposed to infallibility, which
no man claims.

One who believes himself to be fallible
may still hold it to be certain that two and
two make four, and that two contradictory
propositions cannot both be true. He may
believe some things to be probable only,
and other things to be demonstrable, with-
out making any pretence to infallibility.

If we use words in their proper meaning,
it is impossible that demonstration should
degenerate into probability from the imper-
fection of our faculties. Our judgment can-
not change the nature of the things about
which we judge. What is really demon-
stration, will still be so, whatever judgment
we form concerning it. It may, likewise,
be observed, that, when we mistake that foi
demonstration which really is not, the con-
sequence of this mistake is, not that de-
monstration degenerates into probability,
but that what we took to be demonstration
is no proof at all ; for one false step in .a
demonstration destroys the whole, but can-
not turn it into another kind of proof.

Upon the whole, then, this first conclu-
sion of our author, That the fallibility of
human judgment turns all knowledge into
probability, if understood literally, is absurd ;
but, if it be only a figure of speech, and
means no more but that, in all our judg-
ments, we ought to be sensible of our falli-
bility, and ought to hold our opinions with
that modesty that becomes fallible crea-
tures — which I take to be what the author
meant — this, I think, nobody denies, nos



[essay VII

was it necessary to enter into a laborious
proof of it.

One is never in greater danger of trans-
gressing against the rules of logic than in
attempting to prove what needs no proof.
Of this we have an instance in this very
case ; for the author begins his proof, that
all human judgments are fallible, with af-
firming that some are infallible.

" In all demonstrative sciences," says
he, " the rules are certain and infallible ;
but when we apply them, our fallible and
uncertain faculties are very apt to depart
from them, and fall into error."

He had forgot, surely, that the rules of
demonstrative sciences are discovered by
our fallible and uncertain faculties, and
have no authority but that of human judg-
ment. If they be infallible, some human
judgments are infallible'; and there are many
in various branches of human knowledge
which have as good a claim to infallibility
as the rules of the demonstrative sciences.

We have reason here to find fault with
our author for not being sceptical enough,
as well as for a mistake in reasoning, when
he claims infallibility to certain decisions of
the human faculties, in order to prove that
all their decisions are fallible.

The second point which he attempts to
prove is, That this probability, when duly
examined, suffers a continual diminution,
and at last a total extinction.

The obvious consequence of this is, that
no fallible being can have good reason to
believe anything at all ; but let us hear the
proof. [702]

" In every judgment, we ought to cor-
rect the first judgment derived from the
nature of the object, by another judgment
derived from the nature of the understand-
ing. Beside the original uncertainty inher-
ent in the subject, there arises another,
derived from the weakness of the faculty
which judges. Having adjusted these two
uncertainties together, we are obliged, by
our reason, to add a new uncertainty, de-
rived from the possibility of error in the
estimation we make of the truth and fidelity
of our faculties. This is a doubt of which,
if we would closely pursue our reasoning,
we cannot avoid giving a decision. But
this decision, though it should be favour-
able to our preceding judgment, being
founded only on probability, must weaken
still farther our first evidence. The third
uncertainty must, in like manner be criti-
cised by a fourth, and so on without end.

" Now, as every one of these uncertainties
takes away a part of the original evidence,
it must at last be reduced to nothing. Let
our first belief be ever so strong, it must in-
fallibly perish, by passing through so many
examinations, each of which carries off
somewhat of its force and vigour. No finite

object can subsist under a decrease repeated
in infinitum.

" When I reflect on the natural fallibil-
ity of my judgment, I have less confidence
in my opinions than when I only consider
the objects concerning which I reason. And
when I proceed still farther, to turn the scru-
tiny against every successive estimation I
make of my faculties, all the rules of logic
require a continual diminution, and at last
a total extinction of belief and evidence."

This is the author's Achillean argument
against the evidence of reason, from which
he concludes, that a man who would govern
his belief by reason must believe nothing at
all, and that belief is an act, not of the co-
gitative, but of the sensitive part of our
nature. [703]

If there be any such thing as motion,
(said an ancient Sceptic,*) the swift-footed
Achilles could never overtake an old man
in a journey. For, suppose the old man to
set out a* thousand paces before Achilles,
and that, while Achilles has travelled the
thousand paces, the old man has gone five
hundred ; when Achilles has gone the five
hundred, the old man has gone two hun-
dred and fifty ; and when Achilles has
gone the two hundred and fifty, the old
man is still one hundred and twenty-five
before him. Repeat these estimations in
infinitum, and you will still find the old man
foremost ; therefore Achilles can never
overtake him ; therefore there can be no
such thing as motion.

The reasoning of the modern Sceptic
against reason is equally ingenious, and
equally convincing. Indeed, they have a
great similarity.

If we trace the journey of Achilles two
thousand paces, we shall find the very
point where the old man is overtaken. But
this short journey, by dividing it into an
infinite number of stages, with correspond-
ing estimations, is made to appear infinite.
In like manner, our author, subjecting
every judgment to an infinite number of
successive probable estimations, reduces
the evidence to nothing.

To return then to the argument of the
modern Sceptic. I examine the proof of a
theorem of Euclid. It appears to me to be
strict demonstration. But I may have
overlooked some fallacy; therefore I ex-
amine it again and again, but can find no
flaw in it. I find all that have examined
it agree with me. I have now that evidence
of the truth of the proposition which I and
all men call demonstration, and that belief
of it which we call certainty. [704]

Here my sceptical friend interposes, and
assures me, that the rules of logic reduce

* Zeno Eleates. He is improperly called, simpli-
nter, ■ Sceptic H. '



this demonstration to no evidence at all.
1 am willing to hear what step in it he thinks
fallacious, and why. He makes no objec-
tion to any part of the demonstration, but
pleads my fallibility in judging. I have
made the proper allowance for this already,
by being open to conviction. But, says he,
there are two uncertainties, the first inherent
in the subject, which I have already shewn
to have only probable evidence ; the second
arising from the weakness of the faculty
that judges. I answer, it is the weakness of
the faculty only that reduces this demonstra-
tion to what you call probability. You
must not therefore make it a second uncer-
tainty; for it is the same with the first.
To take credit twice in an account for
the same article is not agreeable to the
rules of logic. Hitherto, therefore, there
is but one uncertainty— to wit, my fallibility
in judging.

But, says my friend, you are obliged by
reason to add a new uncertainty, derived
from the possibility of error in the estima-
tion you make of the truth and fidelity of
your faculties. I answer —

This estimation is ambiguously ex-
pressed ; it may either mean an estimation
of my liableness to err by the misapplica-
tion and abuse of my faculties ; or it may
mean an estimation of my liableness to err
by conceiving my faculties to be true and
faithful, while they may be false and falla-
cious in themselves, even when applied in
the best manner. I shall consider this
estimation in each of these senses.

If the first be the estimation meant, it is
true that reason directs us, as fallible crea-
tures, to carry along with us, in all our
judgments, a sense of our fallibility. It is
true also, that we are in greater danger of
erring in some cases, and less in others ;
and that this danger of erring may, accord-
ing to the circumstances of the case, admit
of an estimation, which we ought likewise
to carry along with us in every judgment
we form. [705]

When a demonstration is short and plain ;
when the point to be proved does not
touch our interest or our passions ; when
the faculty of judging, in such cases, has
acquired strength by much exercise — there is
less danger of erring ; when the contrary
circumstances take place, there is more.

In the present case, every circumstance
is favourable to the j udgment I have formed.
There cannot be less danger of erring in
any case, excepting, perhaps, when I judge
of a self-evident axiom.

The Sceptic farther urges, that this deci-
sion, though favourable to my first judg-
ment, being founded only on probability,
must still weaken the evidence of that judg-

Here I cannot help being of a quite con-
1705, 7061

trary opinion ; nor can I imagine how an
ingenious author could impose upon himself
so grossly ; for surely he did not intend to
impose upon his reader.

After repeated examination of a propo-
sition of Euclid, I judge it to be strictly
demonstrated ; this is my first judgment.
But, as I am liable to err from various
causes, I consider how far I may have been
misled by any of these causes in this judg-
ment. My decision upon this second point
is favourable to my first judgment, and
therefore, as I apprehend, must strengthen
it. To say that this decision, because it is
only probable, must weaken the first evi-
dence, seems to me contrary to all rules of
logic, and to common sense.

The first judgment may be compared to
the testimony of a credible witness ; the
second, after a scrutiny into the character
of the witness, wipes off every objection
that can be-made to it, and therefore surely
must confirm and not weaken his testi-
mony. [706]

But let us suppose, that, in another case,s
I examine my first judgment upon some
point, and find that it was attended with
unfavourable circumstances, what, in rea-
son, and according to the rules of logic,
ought to be the effect of this discovery ?

The effect surely will be, and ought to
be, to make me less confident in my first
judgment, until I examine the point anew
in more favourable circumstances. If it
be a matter of importance, I return to
weigh the evidence of my first judgment.
If it was precipitate before, it must now be
deliberate in every point. If, at first, I
was in passion, I must now be cool. If I
had an interest in the decision, I must
place the interest on the other side.

It is evident that this review of the sub-
ject may confirm my first judgment, not-
withstanding the suspicious circumstances
that attended it. Though the judge was
biassed or corrupted, it does not follow that
the sentence was unjust. The rectitude of
the decision does not depend upon the cha-
racter of the judge, but upon the nature of
the case. From that only, it must be deter-
mined whether the decision be just. The
circumstances that rendered it suspicious
are mere presumptions, which have no force
against direct evidence.

Thus, I have considered the effect of this
estimation of our liableness to err in our
first judgment, and have allowed to it all
the effect that reason and the rules of logic
permit. In the case I first supposed, and
in every case where we can discover no
cause of error, it affords a presumption in
favour of the first judgment. In other
cases, it may afford a presumption against
it. But the rules of logic require, that we
should not judge by presumptions, xhere




we have direct evidence. The effect of an
unfavourable presumption should only be,
to make us examine the evidence with the
greater care. • [707]

The sceptic urges, in the last place, that
this estimation must be subjected to another
estimation, that to another, and so on, in in-
finitum ; and as every new estimation takes
away from the evidence of the first judg-
ment, it must at last be totally annihilated.

I answer, first, It has been shewn above,
that the first estimation, supposing it un-
favourable, can only afford a presumption
against the first judgment ; the second,
upon the same supposition, will be only the
presumption of a presumption ; and the
third, the presumption that there is a pre-
sumption of a presumption. This infinite
series of presumptions resembles an infinite
series of quantities, decreasing in geome-
trical proportion, which amounts only to a
finite sum. The infinite series of stages of
Achilles'sjourney after the old man, amounts
only to two thousand paces ; nor can this

Online LibraryThomas ReidThe works of Thomas Reid, D.D.; now fully collected, with selections from his umpublished letters → online text (page 109 of 114)