em of a
contrary nature, this determination, though full and perfect in itself,
presents us with no steady object, but offers us a number of disagreeing
images in a certain order and proportion. The first impulse, therefore,
is here broke into pieces, and diffuses itself over all those images, of
which each partakes an equal share of that force and vivacity, that is
derived from the impulse. Any of these past events may again happen;
and we judge, that when they do happen, they will be mixed in the same
proportion as in the past.

If our intention, therefore, be to consider the proportions of contrary
events in a great number of instances, the images presented by our past
experience must remain in their FIRST FORM, and preserve their first
proportions. Suppose, for instance, I have found by long observation,
that of twenty ships, which go to sea, only nineteen return. Suppose
I see at present twenty ships that leave the port: I transfer my past
experience to the future, and represent to myself nineteen of these
ships as returning in safety, and one as perishing. Concerning this
there can be no difficulty. But as we frequently run over those several
ideas of past events, in order to form a judgment concerning one single
event, which appears uncertain; this consideration must change the FIRST
FORM of our ideas, and draw together the divided images presented
by experience; since it is to it we refer the determination of that
particular event, upon which we reason. Many of these images are
supposed to concur, and a superior number to concur on one side. These
agreeing images unite together, and render the idea more strong and
lively, not only than a mere fiction of the imagination, but also than
any idea, which is supported by a lesser number of experiments. Each new
experiment is as a new stroke of the pencil, which bestows an additional
vivacity on the colours without either multiplying or enlarging the
figure. This operation of the mind has been so fully explained in
treating of the probability of chance, that I need not here endeavour to
render it more intelligible. Every past experiment may be considered as
a kind of chance; I it being uncertain to us, whether the object will
exist conformable to one experiment or another. And for this reason
every thing that has been said on the one subject is applicable to both.

Thus upon the whole, contrary experiments produce an imperfect belief,
either by weakening the habit, or