reflection produces the custom in an oblique and artificial manner. I
explain myself. It is certain, that not only in philosophy, but even in
common life, we may attain the knowledge of a particular cause merely by
one experiment, provided it be made with judgment, and after a careful
removal of all foreign and superfluous circumstances. Now as after one
experiment of this kind, the mind, upon the appearance either of the
cause or the effect, can draw an inference concerning the existence of
its correlative; and as a habit can never be acquired merely by one
instance; it may be thought, that belief cannot in this case be esteemed
the effect of custom. But this difficulty will vanish, if we consider,
that though we are here supposed to have had only one experiment of a
particular effect, yet we have many millions to convince us of this
principle; that like objects placed in like circumstances, will always
produce like effects; and as this principle has established itself by a
sufficient custom, it bestows an evidence and firmness on any opinion, to
which it can be applied. The connexion of the ideas is not habitual after
one experiment: but this connexion is comprehended under another
principle, that is habitual; which brings us back to our hypothesis. In
all cases we transfer our experience to instances, of which we have no
experience, either expressly or tacitly, either directly or indirectly.

I must not conclude this subject without observing, that it is very
difficult to talk of the operations of the mind with perfect propriety
and exactness; because common language has seldom made any very nice
distinctions among them, but has generally called by the same term all
such as nearly resemble each other. And as this is a source almost
inevitable of obscurity and confusion in the author; so it may frequently
give rise to doubts and objections in the reader, which otherwise he
would never have dreamed of. Thus my general position, that an opinion or
belief is nothing but a strong and lively idea derived from a present