ry. The custom operates before we have time for
reflection. The objects seem so inseparable, that we interpose not
a moment's delay in passing from the one to the other. But as this
transition proceeds from experience, and not from any primary connexion
betwixt the ideas, we must necessarily acknowledge, that experience
may produce a belief and a judgment of causes and effects by a secret
operation, and without being once thought of. This removes all pretext,
if there yet remains any, for asserting that the mind is convinced
by reasoning of that principle, that instances of which we have no
experience, must necessarily resemble those, of which we have. For we
here find, that the understanding or imagination can draw inferences
from past experience, without reflecting on it; much more without
forming any principle concerning it, or reasoning upon that principle.

In general we may observe, that in all the most established and uniform
conjunctions of causes and effects, such as those of gravity, impulse,
solidity, &c. the mind never carries its view expressly to consider any
past experience: Though in other associations of objects, which are more
rare and unusual, it may assist the custom and transition of ideas by
this reflection. Nay we find in some cases, that the reflection produces
the belief without the custom; or more properly speaking, that the
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. Th