quality alone is to the fancy a sufficient bond and association. It is
likewise evident that as the senses, in changing their objects, are
necessitated to change them regularly, and take them as they lie
CONTIGUOUS to each other, the imagination must by long custom acquire the
same method of thinking, and run along the parts of space and time in
conceiving its objects. As to the connexion, that is made by the relation
of cause and effect, we shall have occasion afterwards to examine it to
the bottom, and therefore shall not at present insist upon it. It is
sufficient to observe, that there is no relation, which produces a
stronger connexion in the fancy, and makes one idea more readily recall
another, than the relation of cause and effect betwixt their objects.

That we may understand the full extent of these relations, we must
consider, that two objects are connected together in the imagination, not
only when the one is immediately resembling, contiguous to, or the cause
of the other, but also when there is interposed betwixt them a third
object, which bears to both of them any of these relations. This may be
carried on to a great length; though at the same time we may observe, that
each remove considerably weakens the relation. Cousins in the fourth
degree are connected by causation, if I may be allowed to use that term;
but not so closely as brothers, much less as child and parent. In general
we may observe, that all the relations of blood depend upon cause and
effect, and are esteemed near or remote, according to the number of
connecting causes interposed betwixt the persons.

Of the three relations above-mentioned this of causation is the most
extensive. Two objects may be considered as placed in this relation, as
well when one is the cause of any of the actions or motions of the other,
as when the former is the cause of the existence of the latter. For as
that action or motion is nothing but the object itself, considered in a