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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