by dividing and afterwards joining in
different parts, that perfect habit, which makes us conclude in general,
that instances, of which we have no experience, must necessarily
resemble those of which we have.

To justify still farther this account of the second species of
probability, where we reason with knowledge and reflection from
a contrariety of past experiments, I shall propose the following
considerations, without fearing to give offence by that air of subtilty,
which attends them. Just reasoning ought still, perhaps, to retain
its force, however subtile; in the same manner as matter preserves its
solidity in the air, and fire, and animal spirits, as well as in the
grosser and more sensible forms.

First, We may observe, that there is no probability so great as not to
allow of a contrary possibility; because otherwise it would cease to be
a probability, and would become a certainty. That probability of causes,
which is most extensive, and which we at present examine, depends on a
contrariety of experiments: and it is evident An experiment in the past
proves at least a possibility for the future.

Secondly, The component parts of this possibility and probability are of
the same nature, and differ in number only, but not in kind. It has been
observed, that all single chances are entirely equal, and that the
only circumstance, which can give any event, that is contingent, a
superiority over another is a superior number of chances. In like
manner, as the uncertainty of causes is discovery by experience, which
presents us with a view of contrary events, it is plain, that when we
transfer the past to the future, the known to the unknown, every past
experiment has the same weight, and that it is only a superior number
of them, which can throw the ballance on any side. The possibility,
therefore, which enters into every reasoning of this kind, is composed
of parts, which are of the same nature both among themselves, and with
those, that compose the opposite probability.

Thirdly, We may establish it as a certain maxim, that in all moral as
well as natural phaenomena, wherever any cause consists of a number
of parts, and the effect encreases or diminishes, according to the
variation of that number, the effects properly speaking, is a compounded
one, and arises from the union of the several effects, that proceed from
each part of the cause. Thus, because the gravity of a body encreases or
diminishes by the encrease o