extremes. What we may in general affirm concerning these three acts of
the understanding is, that taking them in a proper light, they all
resolve themselves into the first, and are nothing but particular ways of
conceiving our objects. Whether we consider a single object, or several;
whether we dwell on these objects, or run from them to others; and in
whatever form or order we survey them, the act of the mind exceeds not a
simple conception; and the only remarkable difference, which occurs on
this occasion, is, when we join belief to the conception, and are
persuaded of the truth of what we conceive. This act of the mind has
never yet been explaind by any philosopher; and therefore I am at liberty
to propose my hypothesis concerning it; which is, that it is only a strong
and steady conception of any idea, and such as approaches in some measure
to an immediate impression. [Footnote 5.]

[Footnote 5. Here are the heads of those arguments, which lead us to this
conclusion. When we infer the existence of an object from that of others,
some object must always be present either to the memory or senses, in
order to be the foundation of our reasoning; since the mind cannot run up
with its inferences IN INFINITUM. Reason can never satisfy us that the
existence of any one object does ever imply that of another; so that when
we pass from the impression of one to the idea or belief of another, we
are not determined by reason, but by custom or a principle of association.
But belief is somewhat more than a simple idea. It is a particular manner
of forming an idea: And as the same idea can only be varyed by a variation
of its degrees of force and vivacity; it follows upon the whole, that
belief is a lively idea produced by a relation to a present impression,
according to the foregoing definition.]

This operation of the mind, which forms the belief of any matter of fact,
seems hitherto to have been one of the greatest mysteries of philosophy;