This is all I think necessary to observe concerning those four relations,
which are the foundation of science; but as to the other three, which
depend not upon the idea, and may be absent or present even while that
remains the same, it will be proper to explain them more particularly.
These three relations are identity, the situations in time and place, and
causation.

All kinds of reasoning consist in nothing but a comparison, and a
discovery of those relations, either constant or inconstant, which two or
more objects bear to each other. This comparison we may make, either when
both the objects are present to the senses, or when neither of them is
present, or when only one. When both the objects are present to the
senses along with the relation, we call this perception rather than
reasoning; nor is there in this case any exercise of the thought, or any
action, properly speaking, but a mere passive admission of the
impressions through the organs of sensation. According to this way of
thinking, we ought not to receive as reasoning any of the observations we
may make concerning identity, and the relations of time and .place; since
in none of them the mind can go beyond what is immediately 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