ediately present
to the senses, either to discover the real existence or the relations
of objects. It is only causation, which produces such a connexion, as
to give us assurance from the existence or action of one object, that it
was followed or preceded by any other existence or action; nor can the
other two relations be ever made use of in reasoning, except so far
as they either affect or are affected by it. There is nothing in any
objects to perswade us, that they are either always remote or always
contiguous; and when from experience and observation we discover, that
their relation in this particular is invariable, we, always conclude
there is some secret cause, which separates or unites them. The same
reasoning extends to identity. We readily suppose an object may continue
individually the same, though several times absent from and present
to the senses; and ascribe to it an identity, notwithstanding the
interruption of the perception, whenever we conclude, that if we had
kept our eye or hand constantly upon it, it would have conveyed an
invariable and uninterrupted perception. But this conclusion beyond the
impressions of our senses can be founded only on the connexion of cause
and effect; nor can we otherwise have any security, that the object is
not changed upon us, however much the new object may resemble that which
was formerly present to the senses. Whenever we discover such a perfect
resemblance, we consider, whether it be common in that species of
objects; whether possibly or probably any cause coued operate in
producing the change and resemblance; and according as we determine
concerning these causes and effects, we form our judgment concerning the
identity of the object.

Here then it appears, that of those three relations, which depend not
upon the mere ideas, the only one, that can be traced beyond our senses
and informs us of existences and objects, which we do not see or feel,
is causation. This relation, therefore, we shall endeavour to explain
fully before we leave the subject of the understanding.

To begin regularly, we must consider the idea of causation, and see from
what origin it is derived. It is impossible to reason justly, without
understanding perfectly the idea concerning which we reason; and it is
impossible perfectly to understand any idea, without tracing it up to
its origin, and examining that primary impression, from which it arises.
The examination of the impression bestows a clear