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An Enquiry Concerning Human Understanding

assurance, and regards his past experience as a full proof 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 probability. 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.
88. 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 experience 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 villany, 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 proof or a
probability, 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.
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