ation or association in the
fancy betwixt the impression and idea; so that there can be no suspicion
of mistake.

In order to put this whole affair in a fuller light, let us consider
it as a question in natural philosophy, which we must determine by
experience and observation. I suppose there is an object presented, from
which I draw a certain conclusion, and form to myself ideas, which I
am said to believe or assent to. Here it is evident, that however that
object, which is present to my senses, and that other, whose existence
I infer by reasoning, may be thought to influence each other by their
particular powers or qualities; yet as the phenomenon of belief, which
we at present examine, is merely internal, these powers and qualities,
being entirely unknown, can have no hand in producing it. It is the
present impression, which is to be considered as the true and real
cause of the idea, and of the belief which attends it. We must therefore
endeavour to discover by experiments the particular qualities, by which
it is enabled to produce so extraordinary an effect.

First then I observe, that the present impression has not this effect
by its own proper power and efficacy, and when considered alone, as
a single perception, limited to the present moment. I find, that
an impression, from which, on its first appearance, I can draw no
conclusion, may afterwards become the foundation of belief, when I have
had experience of its usual consequences. We must in every case have
observed the same impression in past instances, and have found it to be
constantly conjoined with some other impression. This is confirmed by
such a multitude of experiments, that it admits not of the smallest
doubt.

From a second observation I conclude, that the belief, which attends the
present impression, and is produced by a number of past impressions and
conjunctions; that this belief, I say, arises immediately, without any
new operation of the reason or imagination. Of this I can be certain,
because I never am conscious of any such operation, and find nothing
in the subject, on which it can be founded. Now as we call every thing
CUSTOM, which proceeds from a past repetition, without any new reasoning
or conclusion, we-may establish it as a certain truth, that all the
belief, which follows upon any present impression, is derived solely
from that origin. When we are accustomed to see two impressions
conjoined together, the appearance or idea of the on