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experience； because it commonly informs us beforehand of the
uncertainty； by that contrariety of events； which we may
learn from a diligent observation。 All effects follow not
with like certainty from their supposed causes。 Some events
are found； in all countries and all ages； to have been
constantly conjoined together： Others are found to have been
more variable； and sometimes to disappoint our expectations；
so that； in our reasonings concerning matter of fact； there
are all imaginable degrees of assurance； from the highest
certainty to the lowest species of moral evidence。
A wise man； therefore； proportions his belief to the
evidence。 In such conclusions as are founded on an
infallible experience； he expects the event with the last
degree of assurance； and regards his past experience as a
full of the future existence of that event。 In other
cases； he proceeds with more caution： He weighs the opposite
experiments： He considers which side is supported by the
greater number of experiments： To that side he inclines；
with doubt and hesitation； and when at last he fixes his
judgement； the evidence exceeds not what we properly call
。 All probability； then； supposes an opposition
of experiments and observations； where the one side is found
to overbalance the other； and to produce a degree of
evidence； proportioned to the superiority。 A hundred
instances or experiments on one side； and fifty on another；
afford a doubtful expectation of any event； though a hundred
uniform experiments； with only one that is contradictory；
reasonably beget a pretty strong degree of assurance。 In all
cases； we must balance the opposite experiments； where they
are opposite； and deduct the smaller number from the
greater； in order to know the exact force of the superior
evidence。
To apply these principles to a particular instance； we
may observe； that there is no species of reasoning more
common； more useful； and even necessary to human life； than
that which is derived from the testimony of men； and the
reports of eye… witnesses and spectators。 This species of
reasoning； perhaps； one may deny to be founded on the
relation of cause and effect。 I shall not dispute about a
word。 It will be sufficient to observe that our assurance in
any argument of this kind is derived from no other principle
than our observation of the veracity of human testimony； and
of the usual conformity of facts to the reports of
witnesses。 It being a general maxim； that no objects have
any discoverable connexion together； and that all the
inferences； which we can draw from one to another； are
founded merely on our experience of their constant and
regular conjunction； it is evident； that we ought not to
make an exception to this maxim in favour of human
testimony； whose connexion with any event seems； in itself；
as little necessary as any other。 Were not the memory
tenacious to a certain degree； had not men commonly an
inclination to truth and a principle of probity； were they
not sensible to shame； when detected in a falsehood： Were
not these； I say； discovered by to be
qualities； inherent in human nature； we should never repose
the least confidence in human testimony。 A man delirious； or
noted for falsehood and villainy； has no manner of authority
with us。
And as the evidence； derived from witnesses and human
testimony； is founded on past experience； so it varies with
the experience； and is regarded either as a or a
； according as the conjunction between any
particular kind of report and any kind of object has been
found to be constant or variable。 There are a number of
circumstances to be taken into consideration in all
judgements of this kind； and the ultimate standard； by which
we determine all disputes； that may arise concerning them；
is always derived from experience and observation。 Where
this experience is not entirely uniform on any side； it is
attended with an unavoidable contrariety in our judgements；
and with the same opposition and mutual destruction of
argument as in every other kind of evidence。 We frequently
hesitate concerning the reports of others。 We balance the
opposite circumstances； which cause any doubt or
uncertainty； and when we discover a superiority on any side；
we incline to it； but still with a diminution of assurance；
in proportion to the force of its antagonist。
This contrariety of evidence； in the present case； may
be derived from several different causes； from the
opposition of contrary testimony； from the character or
number of the witnesses； from the manner of their delivering
their testimony； or from the union of all these
circumstances。 We entertain a suspicion concerning any
matter of fact； when the witnesses contradict each other；
when they are but few； or of a doubtful character； when they
have an interest in what they affirm； when they deliver
their testimony with hesitation； or on the contrary； with
too violent asseverations。 There are many other particulars
of the same kind； which may diminish or destroy the force of
any argument； derived from human testimony。
Suppose； for instance； that the fact； which the
testimony endeavours to establish； partakes of the
extraordinary and the marvellous； in that case； the
evidence； resulting from the testimony； admits of a
diminution； greater or less； in proportion as the fact is
more or less unusual。 The reason why we place any credit in
witnesses and historians； is not derived from any
； which we perceive ； between testimony
and reality； but because we are accustomed to find a
conformity between them。 But when the fact attested is such
a one as has seldom fallen under our observation； here is a
contest of two opposite experiences； of which the one
destroys the other； as far as its force goes； and the
superior can only operate on the mind by the force； which
remains。 The very same principle of experience； which gives
us a certain degree of assurance in the testimony of
witnesses； gives us also； in this case； another degree of
assurance against the fact； which they endeavour to
establish； from which contradiction there necessarily arises
a counterpoize； and mutual destruction of belief and
authority。
C/ATO； was a proverbial saying in R/OME； even during the
lifetime of that philosophical patriot。＇25＇ The
incredibility of a fact； it was allowed； might invalidate so
great an authority。
The I/NDIAN prince； who refused to believe the first
relations concerning the effects of frost； reasoned justly；
and it naturally required very strong testimony to engage
his assent to facts； that arose from a state of nature； with
which he was unacquainted； and which bore so little analogy
to those events； of which he had had constant and uniform
experience。 Though they were not contrary to his experience；
they were not conformable to it。＇26＇
But in order to encrease the probability against the
testimony of witnesses； let us suppose； that the fact； which
they affirm； instead of being only marvellous； is really
miraculou