Sect. VI. Of Probability*
* Mr. Locke
divides all arguments into demonstrative and probable.
In this view, we must
say, that it is only probable all men must
die, or that the sun
will rise to-morrow. But to conform our
language more to common
use, we ought to divide arguments into
demonstrations, proofs,
and probabilities. By proofs meaning such
arguments from experience
as leave no room for doubt or opposition.
46. THOUGH there be no such
thing as Chance in the world; our
ignorance of the real cause of any
event has the same influence on the
understanding, and begets a like
species of belief or opinion.
There is certainly a probability,
which arises from a superiority of
chances on any side; and according
as this superiority encreases,
and surpasses the opposite chances,
the probability receives a
proportionable encrease, and begets
still a higher degree of belief or
assent to that side, in which we
discover the superiority. If a die
were marked with one figure or number
of spots on four sides, and with
another figure or number of spots
on the two remaining sides, it would
be more probable, that the former
would turn up than the latter;
though, if it had a thousand sides
marked in the same manner, and only
one side different, the probability
would be much higher, and our
belief or expectation of the event
more steady and secure. This
process of the thought or reasoning
may seem trivial and obvious;
but to those who consider it more
narrowly, it may, perhaps, afford
matter for curious speculation.
It seems evident, that, when
the mind looks forward to discover
the event, which may result from
the throw of such a die, it considers
the turning up of each particular
side as alike probable; and this the
very nature of chance, to render
all the particular events,
comprehended in it, entirely equal.
But finding a greater number of
sides concur in the one event than
in the other, the mind is carried
more frequently to that event, and
meets it oftener, in revolving
the various possibilities or chances,
on which the ultimate result
depends. This concurrence of several
views in one particular event
begets immediately, by an inexplicable
contrivance of nature, the
sentiment of belief, and gives that
event the advantage over its
antagonist, which is supported by
a smaller number of views, and
recurs less frequently to the mind.
If we allow, that belief is
nothing but a firmer and stronger
conception of an object than what
attends the mere fictions of the
imagination, this operation may,
perhaps, in some measure, be accounted
for. The concurrence of these
several views or glimpses imprints
the idea more strongly on the
imagination; gives it superior force
and vigour; renders its influence
on the passions and affections more
sensible; and in a word, begets
that reliance or security, which
constitutes the nature of belief
and opinion.
47. The case is the same with
the probability of causes, as with
that of chance. There are some causes,
which are entirely uniform
and constant in producing a particular
effect; and no instance has
ever yet been found of any failure
or irregularity in their operation.
Fire has always burned, and water
suffocated every human creature: The
production of motion by impulse
and gravity is an universal law, which
has hitherto admitted of no exception.
But there are other causes,
which have been found more irregular
and uncertain; nor has rhubarb
always proved a purge, or opium
a soporific to every one, who has
taken these medicines. It is true,
when any cause fails of producing
its usual effect, philosophers ascribe
not this to any irregularity in
nature; but suppose, that some secret
causes, in the particular
structure of parts, have prevented
the operation. Our reasonings,
however, and conclusions concerning
the event are the same as if
this principle had no place. Being
determined by custom to transfer
the past to the future, in all our
inferences; where the past has been
entirely regular and uniform, we
expect the event with the greatest
assurance, and leave no room for
any contrary supposition. But where
different effects have been found
to follow from causes, which are
to appearance exactly similar, all
these various effects must occur to
the mind in transferring the past
to the future, and enter into our
consideration, when we determine
the probability of the event.
Though we give the preference to
that which has been found most usual,
and believe that this effect will
exist, we must not overlook the
other effects, but must assign to
each of them a particular weight and
authority, in proportion as we have
found it to be more or less
frequent. It is more probable, in
almost every country of Europe, that
there will be frost sometime in
January, than that the weather will
continue open throughout that whole
month; though this probability
varies according to the different
climates, and approaches to a
certainty in the more northern kingdoms.
Here then it seems evident,
that, when we transfer the past
to the future, in order to determine
the effect, which will result from
any cause, we transfer all the
different events, in the same proportion
as they have appeared in
the past, and conceive one to have
existed a hundred times, for
instance, another ten times, and
another once. As a great number of
views do here concur in one event,
they fortify and confirm it to
the imagination, beget that sentiment
which we call belief, and give
its object the preference above
the contrary event, which is not
supported by an equal number of
experiments, and recurs not so
frequently to the thought in transferring
the past to the future.
Let any one try to account for this
operation of the mind upon any
of the received systems of philosophy,
and he will be sensible of
the difficulty. For my part, I shall
think it sufficient, if the
present hints excite the curiosity
of philosophers, and make them
sensible how defective all common
theories are in treating of such
curious and such sublime subjects.
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